United States
Environmental Protection
Agency
Office of
Reseach and
Development
Environmental Monitoring
and Support Laboratory
Las Vegas, Nevada 89114
EPA-600/7-77-078
July 1977
FUSION METHOD FOR THE
MEASUREMENT OF PLUTONIUM
IN SOIL: Single-Laboratory
Evaluation of Interlaboratory
Collaborative Test
Interagency
Energy-Environment
Research and Development
Program Report
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into seven series. These seven
broad categories were established to facilitate further development and
application of environmental technology. Elimination of traditional grouping
was consciously planned to foster technology transfer and a maximum
interface in related fields. The seven series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
This report has been assigned to the INTERAGENCY ENERGY-
ENVtRONMENT RESEARCH AND DEVELOPMENT series. Reports in this
series result from the effort funded under the 17-agency Federal
Energy/Environment Research and Development Program. These studies
relate to EPA's mission to protect the public health and welfare from adverse
effects of pollutants associated with energy systems. The goal of the Program
is to assure the rapid development of domestic energy supplies in an
environmentally compatible manner by providing the necessary environ-
mental data and control technology. Investigations include analysis of the
transport of energy-related pollutants and their health and ecological effects;
assessments of, and development of, control technologies for energy systems;
and integrated assessments of a wide range of energy-related environmental issues.
This document is available to the public through the National Technical Infor-
mation Service, Springfield, Virginia 22161.
-------
EPA-600/7-77-078
July 1977
FUSION METHOD FOR THE MEASUREMENT OF PLUTONIUM IN SOIL:
Single-Laboratory Evaluation and Interlaboratory
Collaborative Test
by *
P. B. Hahn, E. W. Bretthauer, P. B. Altringer, and N. F. Mathews
Monitoring Systems Research and Development Division
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
*U.S. Bureau of Mines
Salt Lake City, Utah 84112
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
LAS VEGAS, NEVADA 89114
-------
DISCLAIMER
This report has been reviewed by the Environmental Monitoring and Support
Laboratory-Las Vegas, U.S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
-------
FOREWORD
Protection of the environment requires effective regulatory actions which
are based on sound technical and scientific information. This information must
include the quantitative description and linking of pollutant sources, trans-
port mechanisms, interactions, and resulting effects on man and his environ-
ment. Because of the complexities involved, assessment of specific pollutants
in the environment requires a total systems approach which transcends the media
of air, water, and land. The Environmental Monitoring and Support Laboratory-
Las Vegas contributes to the formation and enhancement of a sound integrated
monitoring data base through multidisciplinary, multimedia programs designed
to:
develop and optimize systems and strategies for moni-
toring pollutants and their impact on the environment
• demonstrate new monitoring systems and technologies by
applying them to fulfill special monitoring needs of
the Agency's operating programs.
This report presents the results of a single-laboratory evaluation and an
interlaboratory collaborative test of a method for measuring plutonium in soil.
The Environmental Protection Agency is presently preparing a Federal Guidance
Document for plutonium-in-soil and the results of this study should provide
valuable input for the Guidance. Such studies are extremely useful as they
demonstrate the state of the art of the analytical methodology which will
ultimately provide the information for decisions associated with environmental
standards and guidelines. Collaborative tests also allow each participating
laboratory to critically evaluate its capabilities in comparison to other
laboratories and often document the need for taking corrective action to im-
prove techniques. For further information, contact the Methods Development and
Analytical Support Branch, Monitoring Systems Research and Development Divi-
sion, Environmental Monitoring and Support Laboratory, Las Vegas, Nevada.
GeoEge p. Morgan
Director
Environmental Monitoring and Support Laboratory
Las Vegas
iii
-------
ABSTRACT
This report presents the results of a single-laboratory evaluation and an
interlaboratory collaborative test of a method for measuring plutonium in soil.
The method employs potassium fluoride and potassium pyrosulfate fusions to
decompose a 10-gram sample, barium sulfate precipitations, solvent extraction
and electrodeposition to isolate the plutonium, and alpha spectrometry to
measure the plutonium. The method is appended to the report.
The single-laboratory evaluation demonstrated that the overall within-
laboratory precision of the method can approach the precision of nuclear
counting statistics alone. The interlaboratory collaborative test showed the
coefficient variation representing differences between laboratories to be
approximately 10% for concentration levels exceeding 1 disintegration per
minute per gram.
Also discussed are several problem areas associated with environmental
actinide analyses. These include the difficulties which may be anticipated in
requiring monitoring laboratories to adopt a specific complex method of this
type. Suggestions are presented for improving agreement between laboratories
by establishing criteria for analytical results rather than requiring specific
methodology.
This report covers a period from January 1, 1974, to September 30, 1976,
and work was completed as of December 31, 1976.
iv
-------
CONTENTS
Page
FOREWORD iii
ABSTRACT iv
LIST OF TABLES vi
ACKNOWLEDGMENTS vii
INTRODUCTION 1
SUMMARY 1
CONCLUSIONS AND RECOMMENDATIONS 2
CHOICE OF METHOD 4
PREPARATION OF REFERENCE MATERIAL 7
SINGLE-LABORATORY EVALUATION 8
PREPARATION OF THE MANUSCRIPT DESCRIBING THE 10
CANDIDATE METHOD
INTERLABORATORY COLLABORATIVE TEST 10
ADDITIONAL CONSIDERATIONS 22
DISCUSSION OF RESULTS 24
REFERENCES 30
APPENDIX: TENTATIVE METHOD FOR THE ANALYSIS OF PLUTONIUM-239 AND
PLUTONIUM-238 IN SOIL (FUSION TECHNIQUE)
v
-------
LIST OF TABLES
Number Page
1. Preparation of Known Soil Samples 7
2. Results of Single-Laboratory Evaluation 9
3. Results of Preliminary Interlaboratory Evaluation 11
4. Results for Sample A 12
5. Results for Sample B 13
6. Results for Sample C 14
7. Results for Sample D9 15
8. Results for Sample D8 16
9. Summary of Collaborative Test Results 18
10. Interlaboratory Calibration of the Plutonium Tracer 19
11. Summary of Precision Data 21
12. t-Test to Detect Method Bias 21
13. Summary of Collaborative Test Results (after recalibration) 25
14. Summary of Precision Data (after recalibration) 26
15. t-Test to Detect Bias (after recalibration) 26
16. Electrodeposition Results 28
VI
-------
ACKNOWLEDGMENTS
The authors wish to express their gratitude to the Radiological Health
Laboratory, Wright-Patterson Air Force Base; the McClellan Air Force Base
Central Laboratory; the Winchester, Massachusetts, Engineering and Analytical
Center, U.S. Food and Drug Administration; the Mound Laboratory - Monsanto
Research Corporation, Miamisburg, Ohio; Eberline Instrument Corporation,
Albuquerque, New Mexico; and the U.S. Environmental Protection Agency, Environ-
mental Monitoring and Support Laboratory, Cincinnati, Ohio, for participating
in this collaborative test.
Special thanks are given to Mr. Claude W. Sill of the U.S. Energy Research
and Development Administration's Health Services Laboratory, Idaho Falls,
Idaho, for his continuing support during this study and for preparing the
reference samples used in the single-laboratory evaluation and the interlabo-
ratory collaborative test.
vii
-------
INTRODUCTION
In early 1974 the U.S. Environmental Protection Agency (EPA) considered
promulgating a standard or guideline to protect against detrimental human
health effects resulting from land surfaces contaminated with plutonium.
Most types of standards or guidelines which could then be envisaged would
require the use of appropriate methodology for measuring plutonium in soil. At
that time a collaboratively tested method for the measurement of plutonium in
soil did not exist. A decision was therefore made to develop a method which
could be used as an EPA Reference Method should the Agency promulgate a "stand-
ard or guideline" requiring one.
EPA policy is to select a single reference method for a single environ-
mental pollutant. A method so designated must have acceptable accuracy and
precision performance characteristics which have been scientifically and
statistically validated by multiple-laboratory collaborative tests under a
variety of anticipated user conditions. The method must be one that can be
readily implemented by prospective user laboratories. This precludes desig-
nation of very expensive, sophisticated methods as reference methods even
though they may be the most accurate methods available.
This study was designed to evaluate one of the best available methods for
measuring plutonium in soil for consideration as an EPA Reference Method.
SUMMARY
This report presents the results of both a single-laboratory evaluation
and an interlaboratory collaborative test of a candidate method for the mea-
surement of plutonium in soil. The method was developed by the U.S. Atomic
Energy Commission's (AEC) Health Services Laboratory at Idaho Falls, Idaho, and
it involves sequential potassium fluoride and potassium pyrosulfate fusions to
decompose the soil matrix (Sill 1974b). The method was chosen for evaluation
after both a critical review of the literature was performed on currently
available methods and after a plutonium-in-soils workshop was held in Las
Vegas, Nevada, in April 1974. The candidate method is included with this
report as an appendix.
The single-laboratory evaluation of the method was conducted at the U.S.
Environmental Protection Agency's Environmental Monitoring and Support Labora-
tory-Las Vegas by performing replicate analyses on soil samples containing
known levels of plutonium ranging from 0.1 to 10 disintegrations per minute per
gram (dpm/g). The standard soils were prepared at the AEC Health Services
-------
Laboratory at Idaho Falls, Idaho. The soils were fired at a high temperature
and are considered to contain plutonium in a highly refractory form. The same
soils were used for the interlaboratory collaborative test.
A preliminary interlaboratory study involving four laboratories was con-
ducted before the full-scale collaborative test in order to obtain information
regarding potential problem areas in the proposed collaborative test and to
obtain comments on the conciseness and clarity of the document describing the
procedural steps of the method. For this preliminary study the laboratories
were provided with a soil sample of known plutonium concentration and requested
to perform the analysis as described in the document.
Six laboratories out of approximately 30 contacted participated in the
interlaboratory collaborative test. They were requested to perform triplicate
analyses of four soil samples containing known levels of plutonium. Each of
the participating laboratories completed a questionnaire regarding the degree
to which they had deviated from the documented method, the problems they had
encountered with the method, and their opinion of the method. After the
results were received, one of the laboratories was found to disagree signifi-
cantly with the other five. Miscalibration of the plutonium tracer used in the
analysis was the suspected cause of this disagreement. It was therefore de-
cided to perform an interlaboratory calibration of the tracers used by the six
laboratories. A calibrated plutonium-239 solution was forwarded to the labo-
ratories with specific instructions on how to standardize their tracer. The
results of the collaborative test were corrected on the basis of the recali-
bration and are presented and evaluated along with the original results.
The statistical evaluation of the interlaboratory collaborative test
followed the general approach suggested by Youden (1975). A separate statis-
tical analysis was made for each sample because the assumption of equal vari-
ance for different activity levels could not be accepted. No attempt was made
to transform the data in order to group samples at different activity levels
for an analysis of variance. Individual results have been provided so that
additional statistical analyses, considered beyond the scope of this report,
may be performed.
CONCLUSIONS AND RECOMMENDATIONS
The single-laboratory evaluation demonstrated the capability of the candi-
date method to achieve a single-laboratory accuracy and precision approaching
that of counting statistics alone when samples containing 1 to 10 dpm/g of
plutonium-239 are analyzed. The results from replicate analyses of 10-g soil
samples at the 6 and 9 dpm 239Pu/g levels indicated a total analysis coef-
ficient of variation on the order of 2% to 3%. Systematic error or bias above
the 2% to 3% level could not be detected, demonstrating essentially complete
exchange between the refractory plutonium in the soil samples and the plutonium
tracer during the fusion operations.
Complete decomposition of the soil matrix was achieved in the fusions for
-------
every standard sample analyzed. This was also found to be true for several
other types of soils investigated. Plutonium recoveries were excellent, aver-
aging 88% ± 7% for the single-laboratory evaluation. The resolution obtained
in the final alpha spectra for all analyses was sufficient to resolve and
quantify plutonium-238 in the presence of plutonium-239 and the plutonium-236
tracer. The method was also found to be applicable to soils containing ex-
tremely large quantities of calcium (up to 80% CaCC^) with only minor modi-
fications.
The single-laboratory evaluation demonstrated a small potential bias for
the method. Protactinium-231, which occurs naturally in soils, quantitatively
follows plutonium through the analysis and it may be difficult to resolve from
or even be mistaken for the plutonium-239 and plutonium-240 peak in the alpha
spectrum. The analysis of blank soils from Idaho and Alabama showed this bias
to be on the order of 0.1 dpm/g.
The interlaboratory collaborative test showed the candidate method, when
used by a typical group of laboratories, to have an overall, between laboratory
single determination coefficient of variation on the order of 10% at concentra-
tion levels in excess of 1 dpm/g. This overall variability increased to ap-
proximately 30% at the 0.1 dpm/g level. The coefficients of variation repre-
senting the precision for replicate analyses performed within a given labora-
tory ranged between 5% and 10% at the 1 and 10 dpm/g concentration levels. The
coefficients of variation representing variability between the laboratories
also ranged between 5% and 10% at the 1 and 10 dpm/g concentration levels.
It was discovered through the questionnaire that the participating labo-
ratories generally had not calibrated the plutonium tracer used in the study as
specified by the candidate method. Because the tracer calibration is consid-
ered to be one of the prime factors in achieving interlaboratory agreement in a
method of this type, it was decided to have each laboratory standardize the
tracer used in the collaborative test against a common, known plutonium-239
solution and to correct and re-evaluate all of their analytical results. The
interlaboratory calibration did not significantly improve the agreement between
the laboratories; however, it allowed the inclusion of one collaborator's data
in the evaluation who had originally deviated from the concensus by more than
40%. The original calibrations of the remaining five collaborators were found
to agree with a coefficient of variation of 4.3%.
The method itself showed no bias. The Student's t-test demonstrated the
grand average for each sample to be statistically equal to the known value at
the 95% confidence level. This was true for the original results of five
laboratories and the corrected results for all six laboratories.
In addition to the tracer calibration, the electrodeposition was another
portion of the method where the collaborators deviated significantly from the
instructions. Three of the laboratories used the prescribed electrodeposition
technique while the other three either used their own technique or modified the
prescribed technique. Both the final plutonium recovery and the quality of
resolution in the final alpha spectrum are greatly dependent on the electro-
deposition. Average recoveries for the collaborators ranged from 35% to 70%
and good resolution was obtained by three laboratories while the other three
-------
reported marginal resolution. There was no correlation between the electro-
deposition technique used and the recoveries and quality of resolution ob-
tained.
The authors cannot at this time make any firm recommendations regarding
the applicability of this method as a reference method. The primary reason is
that no criteria have yet been established for such a reference method. Only
the performance characteristics of this method have been described in this
report. The authors hope these performance characteristics will prove valuable
in establishing the criteria for a reference method.
The method provided excellent results in the single-laboratory evaluation
and in another study documented in the literature (Sill 1974a). Its fusion
techniques make it, in theory, the most applicable of all available methods for
the analysis of the widest variety of soil samples. Any reference method
chosen should be proven equivalent to this method if this method is ultimately
not chosen.
The authors feel that it would be difficult for a typical user laboratory
to adopt this method for routine analysis of large numbers of samples. This
opinion results from our own personal experience with the method, comments from
half the collaborators and from the fact that only 6 of more than 30 labora-
tories contacted actually participated in the collaborative test.
On the basis of this study, four recommendations can be made regarding any
reference actinide method:
1. A common tracer, extensively cross-calibrated by several labora-
tories, should be used by all laboratories performing actinide analyses.
2. Each laboratory should be allowed to use its own proven electro-
deposition technique for cost effectiveness.
3. Performance criteria should be established and each laboratory should
be required to periodically demonstrate that it can meet these criteria by
analyzing reference samples such as those used in this study.
4. Criteria should be set for individual analyses in terms of minimum
acceptable recovery, quality of resolution of the alpha spectrum, maximum
counting error allowed, maximum activity allowed in a reagent blank run simul-
taneously, and a rigidly defined quality assurance program.
With these recommendations a reference method would not be required if
indeed one ever existed. The question of how far one deviated from the method
need never be asked.
CHOICE OF METHOD
Since an environmental plutonium standard for soil had not yet been
promulgated, exact criteria for sensitivity, accuracy and precision for a
-------
plutonium-in-soil reference method were unavailable. Also, there was wide-
spread and well-documented uncertainty in the scientific community as to
whether any of the available methods could meet certain of the anticipated
Agency and user criteria.
The candidate method would have to be reliable, exhibiting reasonable
accuracy and precision, and applicable to the wide variety of soil types found
in the United States. It would have to be capable of accurate analysis of all
chemical and physical forms of plutonium known to exist in the environment
whether at background or highly elevated levels. Also, if the method should
not be applicable to a given sample type, this would have to become unequi-
vocally apparent either during the course of the analysis or from the results
obtained.
The first task was to perform a critical review of currently available
methods. Two approaches were employed. The first approach was to conduct an
internal laboratory screening of potentially applicable methodology by review-
ing the literature and conducting laboratory evaluations. The second approach
was to sponsor a workshop to obtain input from attendees on existing method-
ology.
Agreement on a reference method by recognized scientists in the subject
area was viewed as indispensable to the successful accomplishment of the task,
because an agreement would be invaluable in ultimately obtaining acceptance of
the method by the rest of the scientific community. Such a workshop was spon-
sored by the National Environmental Research Center-Las Vegas* and was held
April 2-3, 1974, in Las Vegas, Nevada. Workshop attendees included principal
scientists from three U.S. Atomic Energy Commission (AEC)t laboratories, two
EPA laboratories, and three private laboratories. These laboratories perform
at least 80 percent of all plutonium-in-soil analyses conducted in the United
States. Scientists from other organizations having expertise in plutonium
analysis also attended, as did selected personnel representing elements of
agencies administratively responsible for plutonium analysis of soil. Included
were two senior scientists from EPA's Office of Radiation Programs, EPA quality
assurance officials, and officials from certain AEC Operations Offices. The
attendees were nearly unanimous in agreeing on certain criteria. Those cri-
teria were as follows:
1. A 10-gram sample size would be adequate for the sensitivity required.
*Effective June 29, 1975, the National Environmental Research Center-Las Vegas
(NERC-LV) was designated the Environmental Monitoring and Support Laboratory-
Las Vegas (EMSL-LV). This Laboratory is one of the three Environmental Moni-
toring and Support Laboratories of the Office of Monitoring and Technical
Support in the U.S. Environmental Protection Agency's Office of Research and
Development.
tEffective January 19, 1975, the AEC was replaced by the U.S. Energy Research
and Development Administration (ERDA) and the U.S. Nuclear Regulatory Com-
mission (NRC).
-------
2. Extremely important considerations in the analysis of soil for
plutonium are the decomposition of the sample, the equilibration of the pluto-
nium tracer with the plutonium in the sample and the extraction of plutonium
from the soil matrix for subsequent purification and counting. Certain forms
of plutonium, especially those which have been fired at high temperatures, are
known to be highly refractory and consequently are difficult to extract from a
soil matrix. The method would have to be applicable to such forms of plu-
tonium.
3. Available methodology for the analysis of plutonium in soils can be
classified into three major groups according to sample decomposition tech-
niques: acid leaching, total dissolution with nitric and hydrofluoric acids,
and total decomposition by sequential potassium fluoride and potassium pyro-
sulfate fusions. Acid-leaching techniques were considered unacceptable because
of the large quantities of residue which generally remain after such treatment.
Total dissolution of soils with nitric and hydrofluoric acids is often not
truly total and small quantities of residue or turbidity remain after 10 grams
of soil have been treated. The fusion technique, however, is known to dissolve
the most refractory and intractable plutonium compounds while at the same time
completely dissolving the soil matrix. This allows for the complete exchange
between the plutonium in the sample and the plutonium-236 tracer used to trace
the plutonium recovery through the analysis.
4. Both fusion and total dissolution techniques have certain advantages
and a representative method from each type should be evaluated.
Based on these criteria, it was decided that a fusion method had the
widest applicability and would be evaluated first. A second method, involving
a total dissolution technique is presently being evaluated and the results will
be reported at a later date.
The candidate method (see Appendix) evaluated in this report is based on a
method developed by the U.S. Atomic Energy Commission's Health Services Labo-
ratory at Idaho Falls, Idaho (Sill 1974b). In this method a known quantity of
plutonium-236 tracer is added to 10 grams of soil which is decomposed com-
pletely by sequential potassium fluoride and potassium pyrosulfate fusions.
The fused sample is dissolved in dilute hydrochloric acid and the plutonium is
isolated and separated from uranium by co-precipitation with barium sulfate.
The barium sulfate is dissolved in perchloric acid, the solution is adjusted to
approximately 2M in aluminum nitrate and the plutonium is reduced to the tetra-
valent state with sodium nitrite and extracted into Aliquat-336 (methyltri-
caprylyl ammonium chloride). The trivalent actinides are separated by scrub-
bing the organic extract with nitric acid, and thorium is separated by scrub-
bing with hydrochloric acid. Plutonium is then stripped with a perchloric-
oxalic acid solution and electrodeposited onto stainless steel disks. Plu-
tonium-236, plutonium-238, and plutonium-239 plus plutonium-240 are determined
by alpha spectrometry.
The candidate method employs these sample decomposition and plutonium
separation techniques coupled with an electrodeposition technique from an
ammonium sulfate solution (Talvitie 1972).
-------
PREPARATION OF REFERENCE MATERIAL
Several soil samples containing known levels of plutonium were prepared as
described in the Quality Assurance Section (Section 8.0) of the candidate
method. Known amounts of plutonium-239 and plutonium- .38 (calibrated as
described in the candidate method) were thoroughly mixed with approximately 200
grams of wet -200 mesh soil and dried under a heat lamp. After drying, the
soil was muffled at approximately 700° C for several hours to convert the
plutonium to a refractory oxide. Plutonium in this form is considered to be
the most difficult to analyze and would therefore be the best test of a candi-
date method.
The spiked soil was pulverized to -200 mesh, sieved and added to approxi-
mately 3 kilograms of unspiked soil. The composite was weighed to determine
the final plutonium concentration and blended for 2 days to ensure homogeneity.
Losses were compensated for by collecting all of the residues from the drying,
pulverizing, and sieving operations and analyzing for plutonium and subtracting
this value from the original amount of plutonium added. The stock soil was
further blended with unspiked soil to prepare the five samples of known plu-
tonium concentrations listed in Table 1. All blending operations were for at
least 24 hours.
TABLE 1. PREPARATION OF KNOWN SOIL SAMPLES
Samples
Stock
D
P
ce
B
A
239Pu Added (dpm)
(6.123 - 0.06b) x 101*
(1464 g)(20.13 dpm/g)
( 983 g)(20.13 dpm/g)
(302.0 g)(8.99 dpm/g)
(390.0 g)(8.99 dpm/g)
( 44.0 g) (8. 99 dpm/g)
Final
Weight
(g)
3012
3277
3428
2632
3893
3498
239pu
Concentration
(dpm/g) C
20.13 ± 0.07
8.99 ± 0.03
5.77 ± 0.02
1.03 ± 0.01
0.901 ± 0.003
0.113 ± 0.001
238pu
Concentration
(dpm/g) C'd
0.309 ± 0.003
0.138 ± 0.001
0.089 ± 0.001
Ti
-
-
aActivity of 239Pu added to original soil.
Activity of 239Pu found in composite residues.
Uncertainty propagated from 2a counting uncertainties in calibration of
tracer, uncertainty in volume of tracer added, and uncertainties in
weighing.
Calculated from 238Pu contaminant in 239Pu tracer used as spike
(238pu/239pu = 0.0152).
eHigher level calcium soil (2-3% CaC03).
-------
SINGLE-LABORATORY EVALUATION
The candidate method was tested by analyzing soil samples (Table 1)
containing the various known levels of plutonium. Table 2 presents the results
of the plutonium-239 analyses performed at our laboratory. Presented in this
table are the individual results plus the la counting error, the length of the
count, the plutonium recovery and the approximate quantity of plutonium-236
tracer used in the analysis. For the two samples (D and P) analyzed several
times, the average (X), the standard deviation of the individual analyses (S ),
the coefficient of variation (C.V. = 100 S /X) and the ratio of the average £o
the known are calculated.
The results obtained demonstrate the capability of the candidate method to
achieve a single-laboratory accuracy and precision approaching that of counting
statistics alone when samples containing 1 to 10 disintegrations per minute per
gram (dpm/g) of plutonium-239 are analyzed.
Systematic error or bias above the 2 to 3 percent level could not be
detected from the analytical results for the 5.77 and 8.99 dpm/g level soils.
Plutonium recoveries averaged 88% ± 7%, providing nearly optimum sensitivity
and precision. Complete decomposition of the soil matrix was achieved during
the fusions for every sample analyzed. This was also the case for several
other types of soil which were decomposed by the fusion techniques. Similar
analytical results have been documented in the literature from the analysis of
soils at the 30- and 0.5-dpm/g levels using a method similar in all respects
except for the electrodeposition (Sill 1974a).
Plutonium-238 results were not reported in this single-laboratory evalu-
ation because of plutonium-238 contamination of the working area caused by
previous experiments with high concentrations of that isotope. Considerable
effort was dedicated to decontamination; however, the lowest blank level
achieved was about 0.5 dpm, which was a significant fraction of the plutonium-
238 in the soils being analyzed. Although numerical results could not be
reported, the resolution obtained in the final alpha spectra was sufficient to
resolve and quantify plutonium-238 in the presence of plutonium-239 and the
plutonium-236 tracer.
Some outside laboratories questioned whether the method would be appli-
cable to soils containing large quantities of calcium. We experienced no
problem in this regard. A simple modification of the original method allowed
for the analysis of 10 grams of soil containing 80% CaCO^ with plutonium re-
coveries on the order of 60%.
There is one potential weakness in this method: protactinium-231 quanti-
tatively follows plutonium through the analysis and it can, at times, be dif-
ficult to resolve the protactinium-231 peak from the plutonium-239 and pluton-
ium-240 peaks by alpha spectroscopy. The effect is most acute when analyzing
for lower levels of plutonium (<0.2 dpm/g) and apparently negligible at the
higher levels (>1 dpm/g). The analysis of blank soils from Idaho and Alabama
indicated protactinium-231 levels on the order of 0.1 dpm/g and a positive
8
-------
TABLE 2. RESULTS OF SINGLE-LABORATORY EVALUATION
Known
239Pu Level Result
(dpm/g) (dpm/g)a
8.99 8.79 ± 0.20
8.76 ± 0.10
8.72 ± 0.18
8.61 ± 0.11
9.32 ± 0.26
8.78 ± 0.31
8.60 ± 0.10
X = 8.797 S = 0.243 C.V.
X
5.77 5.77 ± 0.05
5.82 ± 0.08
5.88 ± 0.07
5.78 ± 0.07
5.83 ± 0.09
5.65 ± 0.08
5.66 ± 0.15
5.47 ± 0.15
X: = 5.733 S = 0.133 C.V.
X
0.901 0.858 ± 0.025
0.844 ± 0.025
1.03d 1.014 ± 0.025
1.003 ± 0.016
6.36e 6.79 ± 0.25
5.94 ± 0.22
Length
of Count
(Min)
312
1246
363
1013
271
128
1298
= 2.8%
2502
1408
1330
1463
935
965
300
239
= 2.3%
1162
1190
1513
3864
100
100
236pu Tracer Plutonium
Used Recovery
(Approx. dpm) (%)
50 88
92
92
91
68
88
91
X/Known = 0.979 ± 0.025b
50 88
61C
83
88
81
87
79
93
X/Known = 0.994 ± 0.019b
10 93
89
10 92
95
500 57
64
Average Recovery = 88 ± 7
Including la counting uncertainty.
Error in X/Known calculated at the 95% confidence level
from (ts //n)/Known Value using the Student t-distribution.
X
"Partial spill of sample.
Soil contained 2% to 3% CaC03.
"Soil contained 80% CaCC.,.
Excluding c and e.
-------
bias of this order of magnitude may be expected for results obtained using the
candidate method. The significance of such a bias cannot be ascertained until
specific EPA guidelines concerning plutonium-239 in soil are established. The
protactinium-231 interferes only with the measurement of plutonium-239 and
would have no effect on a plutonium-238 measurement. The protactinium-231
interference can be completely eliminated by extracting it into diisobutyl-
carbonol (DIBC) just prior to the plutonium extraction (Sill 1976).
PREPARATION OF THE MANUSCRIPT DESCRIBING THE CANDIDATE METHOD
The manuscript describing the method was prepared from the appropriate
publications in the literature with extensive consultation with the primary
authors and others familiar with the various techniques. The descriptions
of individual steps were continuously revised during the single-laboratory
evaluation performed at this laboratory, again consulting with the primary
authors.
Several outside laboratories which expressed interest in the collaborative
testing of the method agreed to analyze a practice sample by the candidate
method and provide results and comments on both the method and the manuscript
describing the method. Table 3 presents the results from four outside labora-
tories attempting the analysis for the first time on sample P containing
5.77 ± 0.02 dpm/g of plutonium-239 and 0.089 ± 0.001 dpm/g of plutonium-238.
The preliminary results from the practice analyses performed by the
outside laboratories were encouraging. Although low and inconsistant plutonium
recoveries were obtained by two of the laboratories, this was understandable as
a certain amount of experience by the analyst is necessary before optimum
results can be expected. A similar situation existed at our laboratory when we
first attempted the method. The internal precision exhibited by each of the
laboratories was excellent, especially in view of the fact they were provided
with only enough sample to perform triplicate analyses. Differences between
three of the outside laboratories and this laboratory (see previous section)
appeared minor, being on the order of 5%.
Each of these four laboratories plus another which did not perform the
analyses provided excellent comments for revising the wording of several
critical steps in the procedure. These comments were incorporated in the
current revision of the method (see Appendix) which was distributed for the
interlaboratory collaborative test.
INTERLABORATORY COLLABORATIVE TEST
The candidate method was distributed to approximately 30 laboratories
which perform plutonium analyses, requesting their participation in a collab-
orative test which would involve triplicate analysis of four soil samples for
10
-------
TABLE 3. RESULTS OF PRELIMINARY INTERLABORATORY EVALUATION
239pu
Concentration
Laboratory (dpm/g)
W 5.81
5.65
X 5.45a
5.50a
5.34a
Y 5.44
5.51
5.53
Z 4.92b
5.02b'C
Expected
Concentrations 5.77 + 0.02
238pu
Concentration
(dpm/g)
0.072
0.082
0.090
0.070
0.074
0.6
0.4
0.4
0.08
0.08
0.089 ± 0.001
Plutonium
Recovery
(%)
54
52
2
33
53
22
52
37
69
65
Used own electrodeposition technique in sulfate media.
Used plutonium-242 tracer and own electrodeposition technique
in chloride media.
"Used own adaptation of the fusion method.
plutonium-239 and plutonium-238 by the candidate method. Thirteen laboratories
responded and were forwarded 35 grams of soils A, B, C, and D. The labora-
tories which did not participate in the preliminary study were also provided
with 35 grams of the practice sample (P) and its known value and instructed to
try the method before analyzing the test samples.
Six of the thirteen laboratories completed the study and the individual
results are tabulated according to sample in Tables 4-8. Also presented in
each of these tables for each laboratory are averages of the replicate results,
x ; the experimental (within-laboratory) standard deviations, S.; the ratios of
trie average value to the known value; and the plutonium recovery for each of
the analyses. S. is a measure of the random error (precision) for each indi-
vidual laboratory for the given sample and is calculated from Equation 1.
(1)
11
-------
TABLE 4. RESULTS FOR SAMPLE A
(Known Value: 0.113 ± 0.001 dpm 239Pu/g)
Result S.
(dpm/g) (dpm^g)
1 0.18
0.09 0.059
0.07
2 0.12
0.09 0.015
0.10
3 0.22
0.16 0.035
0.16
4 0.136
0.140 0.003
5 0.13
0.13 0.012
0.11
6 0.12
0.09 0.015
0.10
— Ratio of Pu
2£
.,, i , Ave. to Recovery
(dpm^8) Known Cone.3 (%)
9
0.113 1.00 ± 1.30 46
34
52
0.103 0.91 ± 0.33 53
47
92
0.180 1.59 ± 0.77 73
44
68
0.138 1.24 ± 0.24 64
48
0.123 1.09 ± 0.26 17
42
68
0.103 0.91 ± 0.33 66
67
a
Error in the Ratio of Average to Known Concentration calculated at the 95%
confidence level from (tS./Sn.)/Known Value, using the Student t-distribution.
12
-------
TABLE 5. RESULTS FOR SAMPLE B
(Known Value: 0.901 ± 0.003 dpm 239Pu/g)
L Result S.
(dpm/g) (dpm^g)
1 0.84
1.04 0.101
0.91
2 0.75
0.88 0.065
0.81
3 0.89
0.86 0.021
0.90
4 0.94
0.98 0.031
0.92
5 0.82
0.83 0.026
0.87
6 0.40
0.58 0.127
— Ratio of Pu
•yr
, , i , Ave . to Recovery
(dpmfg) Known Cone.3 (%)
28
0.930 1.032 ± 0.278 45
35
56
0.813 0.902 ± 0.179 63
83
75
0.883 0.980 ± 0.058 74
58
87
0.947 1.051 ± 0.085 64
61
38
0.840 0.932 ± 0.072 32
19
66
0.490 0.544 ± 1.266 69
o
Error in the Ratio of Average to Known Concentration calculated at the 95%
confidence level from (tS./*/n7)/Known Value, using the Student t-distribution.
13
-------
TABLE 6. RESULTS OF SAMPLE C
(Known Value: 1.03 ± 0.01 dpm 239Pu/g)
Result S. x.
(dpm/g) (dpm/g) (dpm^g)
1 1.11
1.09 0.020 1.110
1.13
2 0.89
0.91 0.042 0.923
0.97
3 1.00
1.04 0.020 1.020
1.02
4 1.10
1.05 0.050 1.050
1.00
5 0.90
0.94 0.028 0.920
6 0.78
0.71 0.060 0.717
0.66
Ratio of Pu
Ave. to Recovery
Known Cone. (%)
50
1.078 ± 0.048 54
30
24
0.896 ± 0.101 32
69
56
0.990 ± 0.048 82
75
78
1.019 ± 0.121 80
72
69
0.893 ± 0.244 66
39
0.696 ± 0.145 68
66
o
Error in the Ratio of Average to Known Concentration calculated at the 95%
confidence level from (tS./v^TT)/Known Value, using the Student t-distribution.
14
-------
TABLE 7. RESULTS FOR SAMPLE D9
(Known Value: 8.99 + 0.03 dpm 239Pu/g)
Lab
1
2
3
4
5
6
Result
(dpm/g)
11.30
9.32
9.32
8.4
8.4
7.9
8.21
8.22
8.12
9.71
9.17
9.29
7.79
8.26
7.03
6.65
6.30
— Ratio of Pu
(dpijg) (dpm^g) ^^ £°nc a Rec°^ry
34
1.14 9.98 1.110 ± 0.315 35
23
60
0.29 8.23 0.916 ± 0.080 76
63
55
0.06 8.18 0.910 ± 0.017 79
78
61
0.28 9.39 1.044 ± 0.077 76
62
70
0.33 8.03 0.893 ± 0.330 83
67
0.37 6.66 0.741 ± 0.102 69
64
Q
Error in the Ratio of Average to Known Concentration calculated at the 95%
confidence level from (tS ./vnT)/ Known Value, using the Student t-distribution.
15
-------
TABLE 8. RESULTS FOR SAMPLE D8
(Known Value: 0.138 + 0.001 dpm 238Pu/g)
Lab
1
2
3
4
5
6
Result S. x. A^ei0t°£
(dpm/g) (dpm/g) (dpm/g) * a
0.24
0.13 0.055 0.183 1.33 ± 0.99
0.18
0.12
0.12 0.012 0.113 0.82 ± 0.22
0.10
ND
0.49
ND
0.17
0.18 0.006 0.173 1.26 ± 0.11
0.17
0.15
0.13 0.014 0.140 1.01 ± 0.91
0.16
0.13 0.030 0.130 0.94 ± 0.54
0.10
Pu
34
35
23
60
76
63
55
79
78
61
76
62
70
83
67
69
64
3
Error in the Ratio of Average to Known Concentration calculated at the 95%
confidence level from (tS ./v'nT)/Known Value, using the Student t-distribution.
16
-------
where x.. = the individual results (1 through n.) obtained by laboratory i
x. = the average of the individual results for laboratory i
n. = the number of replicates performed by laboratory i
Table 9 summarizes the data for each sample analysis. It presents the
average result (x.) according to laboratory. It shows the grand average of
all the laboratories, X = Z x./m; where m is the number of collaborators and
it gives three additional statistics (S,> S , and S, ) explained and defined
JLater. The results of Laboratory 6 were excluded in the calculation of the
X; S,; S ; and S, statistics.
d r b
Also presented in Table 9 is the ranking test for the laboratories (Youden
1975) to help decide whether a given laboratory has a pronounced systematic
error or bias and if its results should be rejected from the statistical
evaluation of the collaborative study.
Preliminary consideration of the average results immediately places
suspicion on the performance of Laboratory 6. Its results appeared signifi-
cantly low for samples B, C and D9, the three higher level samples where a bias
not associated with contamination would be most apparent. The ranking test
confirms this suspicion, giving Laboratory 6 a score of 28.5. For six labora-
tories and five samples there is less than 5% chance that such a table made up
by a random process will contain a score as large or larger than 28 or as small
or smaller than 7.
Miscalibration of the plutonium-236 tracer was considered the most likely
cause of this bias. Therefore, an intercalibration was performed between the
participating laboratories both to confirm the suspected reason for the Labo-
ratory 6 bias and to assess the validity of an alternate, perhaps more fool-
proof, calibration technique.
The intercalibration involved:
(1) supplying each participant with a calibrated plutonium-239 solution
(Amersham/Searle),
(2) requesting each laboratory to combine measured volumes of the plu-
tonium-239 solution and the plutonium tracer they used in the collaborative
study (VLOO dpm of each), to electroplate the combined tracers and to count the
plate for 1000 minutes by alpha spectrometry, and
(3) having each laboratory provide the referee information on the volumes
of each tracer used, the net counts in the plutonium-236 and plutonium-239
regions of the alpha spectrum and the original value at which their tracer was
calibrated.
The referee calculated the tracer activity for each laboratory based on
the known plutonium-239 activity. Table 10 presents the ratio of the value
of the recalibrated tracer to the original value the laboratories had used.
17
-------
TABLE 9. SUMMARY OF COLLABORATIVE TEST RESULTS
oo
Average Values (x . ) for Samples
Lab ABC
1
2
3
4
5
6b
Known
X
Sd
S
Sb
0.113
0.103
0.180
0.140
0.123
0.103
0.113
0.132
0.0302
0.0333
0.0233
0.930
0.813
0.883
0.947
0.840
0.490
0.901
0.883
0.0571
0.0577
0.0464
1.110
0.923
1.020
1.050
0.920
0.717
1.03
1.005
0.0825
0.0348
0.0800
Analyzed (dpm/g) Ranked Results for Samples Analyzed
D9 D8 A B C D9 D8 Score
9.98 0.183 4211 19
8.23 0.113 5.5 5 4 3 6 23.5
8.18 - 1 3 3 4 3.5 14.5
9.39 0.173 2122 29
8.03 0.140 3 455 3.5 20.5
6.66 0.130 5.5 666 5 28. 5a
8.99 0.138
8.762 0.152
0.871 0.0320
0.583 0.0307
0.803 0.0266
Unusually high score representing consistently low results.
Data from Laboratory 6 not used in statistical analysis.
-------
TABLE 10. INTERIABORATORY CALIBRATION OF THE PLUTONIUM TRACER
Ratio of
Laboratory Recalibrated Value
to Original Value
1
2
b
3
4
5
6
1.011
1.036
1.055
0.943
1.029
1.448
± 0.015
± 0.030
± 0.023
± 0.014
± 0.024
± 0.090
o
Error based on 2o counting uncertainty associated with calibration.
Recalibration performed on new dilution of the same original batch of tracer
which had been used to prepare the tracer used in the collaborative test.
The results of the interlaboratory calibration showed that Laboratory 6
had been significantly out of calibration in comparison to the other labora-
tories and the uncorrected collaborative test data from this laboratory should
not be used in the statistical evaluation of the method. The Dixon test was
used for rejecting this laboratory (Steiner 1975):
"~~ / 1 \
'10 • \ -t1' - 0.778 (2)
n 1
where x = the highest (suspect) value
y., _..v = the next highest value and
x1 = the lowest value
The critical value for this statistic for a sample size of six and an a
risk level of 5% is 0.560.
The statistics S ; S , ; and S, presented in Table 9 are required to
perform the evaluation of the candidate method in terms of the limits of error
which can be expected when the method is used by a typical group of analysts.
In addition to the individual within- laboratory standard deviations (S.)
presented in Tables 4-8, a pooled or combined within- laboratory standard
deviation which is based on the results of all the collaborators for a given
sample is of interest. This statistic, S , is calculated from Equation 3.
m n. _
(Sn±-m) S2. = £ S1 (x±j- x..)2 (3)
19
-------
where n. = the number of replicate determinations performed by labora-
tory i
m = the number of collaborators
x.. = the individual results (1 through n.) obtained by
J laboratory i
x. = the average of the individual results for laboratory i
This statistic is calculated for each sample and is listed in Table 9. Also
presented is the standard deviation of the actual data, S,, which is calculated
from the laboratory averages according to Equation 4.
- -
£ (x. - x)
Sd - 1 I <*>
Of great interest in the evaluation of a method is a statistic which
provides a measure of the differences or precision of the method between labo-
ratories. This statistic, S , the standard deviation of the systematic errors,
is calculated from S and S using Equation 5 (Youden 1975). S is listed
along with S and S, for each sample in Table 9.
o o 7
Sb ' Sd - Sr /k (5)
where k = the number of replicate determinations performed by
the laboratories on a given sample
The collaborative test was designed to evaluate the precision and accu-
racy of the candidate method over two orders of magnitude concentration range
(0.1 to 10 dpm plutonium/gram). Triplicate analyses were performed twice at
both the 0.1 and 1 dpm/g levels and once at the 10 dpm/g level. The statistics
S,, S , and S, were calculated for each series of analyses to evaluate the pre-
cision of the method over the 0.1 to 10 dpm/g concentration range. As men-
tioned earlier, S, is the standard deviation of the actual data based on the
individual laboratory averages of triplicate analyses of a given sample. The
S statistic is the pooled estimate of the within-laboratory standard devia-
tion, and S, is an estimate of the standard deviation of the systematic errors
or differences between laboratories.
Under normal conditions, only a single analysis would be routinely per-
formed on a sample and the evaluation of the precision for this situation is
therefore warranted. For a single analysis the previous estimates of S and
S, would be applicable but S,, the estimate of the total error or precision
between the laboratories, would have to be recalculated from S and S, using
Equation 5 with k = 1. Table 11 summarizes the precision data by listing the
coefficients of variation (100 S/X) for within-laboratory error, systematic
error between laboratories, and the total error between laboratories based on
a single analysis.
The precision data indicate the method has an overall single determination
precision on the order of 10% at levels greater than 1 dpm/g increasing to
approximately 30% at a level of 0.1 dpm/g.
20
-------
TABLE 11. SUMMARY OF PRECISION DATA
Coefficients of
Sample
A
D8
B
C
D9
Known
(dpm/g)
0.113
0.138
0.901
1.03
8.99
X
(dpm/g)
0.132
0.152
0.883
1.005
8.762
Within
Lab
25.2
20.2
6.5
3.5
6.7
Between
Labs
17.7
17.5
5.3
8.0
9.2
Variation (%)
Total
(Single Analysis)
30.8
26.7
8.4
8.7
11.4
It must be emphasized however, that such precision values are only esti-
mates based on a limited number of observations. The within-laboratory error
was based on 14 or 15 observations (9 or 10 degrees of freedom) and the between-
laboratory and total error were based on 5 observations (4 degrees of freedom).
The chi-squared distribution may be used to place a 95% confidence interval on
each of the calculated standard deviations or coefficient of variations (Ostle
1963). For 9 or 10 degrees of freedom, the lower and upper limits are obtained
by multiplying the calculated standard deviation or coefficient of variation by
factors of 0.7 and 1.8 respectively. For 4 degrees of freedom the respective
factors are 0.6 and 2.9.
There appears to be no overall bias to the method when comparing the
average result for each sample to the known value. The t-test was conducted
at the a = 5% risk level for each analysis and in no case does the calculated
value_(Equation 6) exceed the critical value for rejection of the hypothesis
that X equals the known value.
JX - R|
m-1 degrees of freedom
(6)
where R = the known or reference value
m = the number of collaborators
S, = the standard deviation of the data (Equation 4)
d
Table 12 presents the results of the t-test for each of the analyses.
TABLE 12. t-TEST TO DETECT METHOD BIAS
Analysis
m
t-calc. t-crit.
A
D8
B
C
D9
5
4
5
5
5
1.40.
0.88
0.71
0.68
0.59
2.78
3.18
2.78
2.78
2.78
21
-------
ADDITIONAL CONSIDERATIONS
A questionnaire was forwarded to each of the participants to ascertain the
degree to which they had deviated from the documented method and the problems
they had encountered with the method.
The area of major concern was the standardization of the plutonium tracer
as this is considered to be the primary factor in the bias between labora-
tories. Other areas of interest included the quantity of tracer used, modi-
fications in the electrodeposition technique, the degree of resolution between
the alpha peaks in the alpha spectra and the collaborators' opinions of rou-
tinely adapting the procedure. The following paragraphs summarize the major
comments provided by the individual participants.
Laboratory 1 used 22 dpm of plutonium-236 tracer purified by anion ex-
change rather than the recommended procedure. The tracer was standardized as
recommended except the 2ir counter was calibrated using an NBS plutonium-238
standard. A 100-ml platinum dish was used for the fusions. Electrodeposition
was performed using the suggested electrolyte, but at 250 milliamps for 3
hours. The final planchet was flamed before counting and adequate resolution
was achieved to resolve plutonium-236, -238, and -239. The solvent extraction
steps were considered tedious and the laboratory is not willing to run the
procedure routinely.
Laboratory 2 used 12 dpm of plutonium-242 tracer which was not further
purified. Standardization was done as recommended but an NBS gadolinium-148
standard was used to calibrate the 2ir counter. No other modifications of the
procedure were made. Adequate resolution of the plutonium isotopes was
achieved and the laboratory is willing to run the procedure routinely.
Laboratory 3 used 55 dpm of plutonium-236 tracer which was standardized
against a known plutonium-239 standard which had been cross calibrated with
other laboratories. Electrodeposition was performed as recommended but the
plates were generally "very dirty in appearance" compared with plates produced
by their standard technique. Adequate spectral resolution was obtained for
samples A and B, but the plates for samples C and D had to be washed in 6M HC1
to obtain adequate resolution. Although this laboratory stated that a higher
level of effort was required for this method over its standard method, it is
willing to run it on a routine basis.
Laboratory 4 used 22 dpm of plutonium-236 tracer which was not further
purified. Calibration was performed as recommended but using a thin-window
alpha counter and an Eberline Instrument Corp. plutonium-239 source to deter-
mine counter efficiency. Electrodeposition was performed for 2 hours at 450
milliamps after the sample was evaporated to 1 ml of sulfuric acid, diluted,
and neutralized with ammonium hydroxide to the methyl red end point. The
plates were ignited in a flame before counting. The laboratory reported that
no residue was present on the final plates so spectral resolution was assumed
adequate. This laboratory is not willing to run the method on a routine basis
because they found it to be too time consuming.
22
-------
Laboratory 5 used 11 dpm of plutonium-236 tracer which was purified by
anion exchange rather than the recommended procedure. Standardization of the
tracer was performed as recommended, however an NBS plutonium-238 source was
used to calibrate the 2i\ counter. Electrodeposition was performed as recom-
mended. Spectral resolution was considered to be "generally adequate" except
that in some cases (especially Sample C) residue was found on the plates making
it difficult to obtain an accurate determination of plutonium-238 and -239 in
the presence of the plutonium-236 tracer. This laboratory said that the fusion
procedure takes twice as much time as the leaching procedure it normally em-
ploys and would not recommend it on a routine basis, unless resources were
available to support it.
Laboratory 6 used 14 dpm of plutonium-236 tracer purified and calibrated
as recommended except they did not calibrate the 2ir counter with the NBS
americium-241 source concurrent with counting the evaporated tracer. Instead,
they used an efficiency factor that had been determined earlier. During the
interlaboratory calibration it became apparent that the value for this labo-
ratory1 s tracer was approximately 50% low, suggesting that its 2ir counter was
malfunctioning when the tracer was calibrated. Electrodeposition was performed
from a 4% ammonium oxalate - 4M hydrochloric acid solution at 210 milliamps for
2.5 hours. Planchets were flamed before counting and spectral resolution was
considered adequate for plutonium-239 but marginal for plutonium-238. This
laboratory is willing to run the procedure routinely.
The responses to the questionnaire pose some basic questions about the
significance of the collaborative test. Does it represent the collaborators
rigidly following the prescribed method? Or does it represent the collabo-
rators following a general analytical approach? The former is certainly not
true, but the latter does not appear to be strictly true either. The col-
laborators rigidly followed portions of the procedure, i.e., the decomposition
and chemical separation steps, but they generally used their own electrode-
position and calibration techniques.
An important consideration is the fact that in the time frame allotted for
the study, the collaborators were unable to procure a new batch of the tracer
and the necessary NBS americium-241 source to purify and calibrate the tracer
as specified. As a consequence, the collaborators used the tracer they had on
hand which had been calibrated earlier by techniques which were generally
similar to the prescribed technique, but by no means standardized between the
laboratories. The degree of uncertainty contributed to the method from the
tracer calibration can be estimated from the results of the interlaboratory
calibration (Table 10). The five laboratories whose collaborative test results
were evaluated had an average correction factor (recalibrated value/original
value) of 1.015 with a standard deviation of 0.043. This corresponds to a
coefficient of variation of 4.3%. The coefficient of variations representing
the bias between laboratories for the entire method at the 1- and 10-dpm/g
levels ranged between 5% and 9% (Table 11).
To determine whether the interlaboratory calibration significantly im-
proved the results, the same statistical evaluations were performed after
correcting each result by multiplying it by the appropriate correction factor
(Table 10). The results of the collaborative test based on the recalibration
23
-------
are summarized in Tables 13 to 15. The corrected results of Laboratory 6 were
included in this evaluation.
The recalibration did not appear to significantly improve the agreement
between laboratories as might have been expected. The between-laboratory
coefficient of variation remained basically the same for the 1 and 10 dpm/g
concentration levels (6% to 8% after recalibration versus 5% to 9% originally).
We must therefore conclude, when both techniques are done properly, the pro-
posed alternate calibration technique is no better than the combination of
techniques used by the laboratories to originally calibrate their tracer. The
recalibration, however, can serve an important function by providing a check on
suspect results from a given laboratory. As for the original results, there
was no bias detected for the method when the alternate calibration of the
tracer was employed (Table 15).
DISCUSSION OF RESULTS
One conclusion which could be drawn concerning this collaborative study is
perhaps best said in the words of Youden (1969): "If every laboratory departs
capriciously from the procedure as specified, then the whole business of inter-
laboratory testing might as well be forgotten because no single version of the
procedure can be tried out." It would, however, have been indeed unfortunate
had this collaborative test not been conducted due to the valuable information
and insights obtained concerning the state of the art of environmental pluto-
nium analysis and perhaps environmental actinide analysis in general.
The collaborative test, in one sense, could be considered a ruggedness
test for the method (Youden 1975) even though it was not statistically designed
as such and conclusions regarding potential problem areas could not be drawn on
a statistical basis. The test however involved the actual variables affecting
agreement between laboratories, many of which would have been overlooked in a
properly designed single-laboratory ruggedness test. Many of these variables
are not numerical and statistics are of no help in evaluating them.
A greater effort should be placed on standardization of the tracer and
consistency between different batches standardized independently. It was
discovered through this collaborative test that one laboratory was routinely
using two tracers with a calibration bias between the two on the order of 40%.
Another laboratory had an apparent calibration bias of about 20% when it first
submitted the results for the interlaboratory calibration. This was the labo-
ratory which performed the calibration on a new dilution of the originally
calibrated stock solution. However, when the new dilution was prepared an
error was made in calculating the decay factor (1 year was overlooked).
A disconcerting finding emerged when the recalibration of the tracer was
requested. One laboratory had just enough tracer left from the given batch to
perform the recalibration. The laboratory which recalibrated using a different
dilution, did so without even realizing it until certain discrepancies were
pointed out by the referee. This laboratory had none of the original dilution
24
-------
TABLE 13. SUMMARY OF COLLABORATIVE TEST RESULTS
(after recalibration)
Average Values for Samples
Lab A B
1
2
3
4
5
6
Known
X
Sd
S
r
Sb
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
114
107
193
132
127
149
113
137
0311
0327
0247
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
940
842
930
893
864
710
901
863
0838
0785
0705
1.
0.
1.
0.
0.
1.
1.
1.
0.
0.
0.
Analyzed (dpm/g)
C D9
122
956
073
990
947
038
03
021
0691
0478
0633
10.
8.
8.
8.
8.
9.
8.
9.
0.
0.
0.
09
53
63
85
26
64
99
000
711
572
630
D8
0.185
0.117
-
0.163
0.144
0.188
0.138
0.159
0.0297
0.0345
0.0220
Ranked Results for Samples Analyzed
A B C D9 D8 Score9
51112 10
65556 27
1 2 2 4 3.5 12.5
3 3 4 3 3.5 16.5
44665 25
26321 14
For 6 laboratories and 5 samples, the 5% two-tailed limits for ranking scores are 7 and 28.
-------
TABLE 14. SUMMARY OF PRECISION DATA
(after recalibration)
Coefficients of Variation (%)
Sample
A
D8
B
C
D9
Known
(dpm/g)
0.113
0.138
0.901
1.03
8.99
X
(dpm/g)
0.137
0.159
0.863
1.021
9.000
Within
Lab
23.9
21.7
9.1
4.7
6.4
Between
Labs
18.0
13.8
8.2
6.2
7.0
Total
(Single Analysis)
29.9
25.7
12.2
7.8
9.5
TABLE 15. t-TEST TO DETECT BIAS
(after recalibration)
Analysis m t-calc. t-crit.
A
D8
B
C
D9
6
5
6
6
6
1.89
1.58
1.11
0.32
0.03
2.57
2.78
2.57
2.57
2.57
left. If 6 months more had elapsed would any of the laboratories have been
able to recalibrate? Is any laboratory routinely and periodically sealing
portions of its actinide tracers in glass vials to enable it to answer future
questions regarding calibration?
It has been demonstrated that tracer calibration procedures do indeed vary
between laboratories. One laboratory, having the facilities to segregate high-
and low-level operations may perform a calibration using high activities and
short counting times. A laboratory without such facilities must wisely use
much lower levels and longer counting times to avoid potential contamination.
Long counts are more susceptable to error due to long-term instrument vari-
ations. Such an error introduced during the initial calibration of the tracer
would subsequently bias all analytical results based on that tracer.
During the interlaboratory calibration, three of the laboratories cali-
brated the pipets or weighed solutions; the other three did not, even though
they were specifically instructed to do so. One laboratory did not perform
duplicate calibrations as requested and then counted the single sample only
long enough to achieve a 2o counting error of 6%. We must therefore conclude
26
-------
that many laboratories, at times, appear reluctant to take even simple pre-
cautions to reduce the chance and degree of bias. Perhaps the answer here is
to have all of the laboratories involved in environmental actinide analyses
obtain the various tracers from a single batch, prepared and calibrated by the
National Bureau of Standards or another qualified supplier. The laboratories
would then independently recalibrate the supplied tracer only to reconfirm the
certified value and would use only the.certified value in their calculations.
Such an approach would certainly improve the agreement between laboratories for
a method of this type.
There are several comments to be made on how the individual laboratories
handled the analytical portion of the method, the significance of the modi-
fications they employed and the problem areas they encountered.
The collaborating laboratories reported that they did not significantly
modify the sample decomposition or the chemical separation portions of the
procedure. It can thus be assumed that uniform results were obtained in terms
of equilibrating the tracer with the plutonium in the sample and decontami-
nating the plutonium from interfering actinides. Tracer equilibration and
decontamination factors are discussed by the original developers of the method
(Sill 1974b, Sill 1975). The laboratories unfamiliar with the method had
problems mastering certain operations at first, but they felt there would be no
problem once they obtained sufficient experience. This was also true for the
single-laboratory evaluation performed at our laboratory. This inexperience
could be partially responsible for the differences between our laboratory and
the collaborating laboratories in the recoveries and the within-laboratory
coefficient variations at the 1 to 10 dpm/g level (80% to 90% versus 30% to 80%
and 2% to 3% versus 5% to 10%).
One of the most critical variables affecting both the plutonium recovery
and the ability to resolve isotopes of plutonium by alpha spectrometry is the
electrodeposition. Microgram quantities of elements carried through the pro-
cedure from the soil and the reagents, can result in lowered yields and de-
graded spectra (Sill 1974b). Lower yields can be compensated for by longer
counting times, but degraded spectra can seriously affect the accuracy and
precision of the analysis. The effect is more critical for plutonium-238 than
it is for plutonium-239 when plutonium-236 is used as a tracer. Degradation is
also directly proportional to the quantity of tracer used. The laboratories
participating in this study employed a variety of electrodeposition techniques
yielding a variety of results (Table 16).
There appears to be little correlation between the electrodeposition
technique and the quality of results obtained. Marginal to good recoveries
were obtained by the laboratories using the prescribed or their own electrode-
position technique while the laboratory attempting to compromise had signifi-
cantly lower recoveries. No correlation could be made between the quality of
resolution and the electrodeposition technique. Two of the four laboratories
using the prescribed technique obtained good resolution while the other two
obtained marginal resolution. Of the two laboratories using their own tech-
niques, one obtained good resolution while the other did not.
Flaming the planchet before counting can either degrade or improve spec-
tral resolution depending on the condition of the original plate (Sill 1976).
27
-------
TABLE 16. ELECTRODEPOSITION RESULTS
Technique
Laboratory
Planchet
Flamed
Average
Recovery
Spectral
Resolution
As prescribed
2
3
5
This Lab
As prescribed
but low amper-
age
no
no
no
no
yes
56 ± 17
70 ± 14
48 ± 23
88 ± 7
35 ± 12
Good
Marginal
Marginal
Good
Good
Own Technique
4
6
yes
yes
70 ± 9
64 ± 9
Good
Marginal
Including one standard deviation.
Flaming is not recommended for plates having a shiny appearance as it will
generally degrade resolution. Two of the laboratories, however, reported good
resolution in spite of flaming the planchet.
There could be fundamental problems in recommending a specific plutonium
or actinide procedure which has performed well in a given laboratory to the
rest of the scientific community and expecting comparable results. Actinide
procedures are extremely sensitive to analyst technique and an analyst must
thoroughly master the procedural operations before optimum results can be
expected. There can also be subtle and unquantified variables that may crit-
ically affect the outcome of an analysis. These can be attributed to both
technique and/or sample composition. If such variables are undefined they may
be allowed to vary or not be compensated for in the prescribed written pro-
cedure and adversely affect results.
An additional important consideration is that a well-qualified laboratory
may be unwilling to cope with certain specifically defined operations. Such
operations may be those difficult or expensive to tool up for or even incom-
patible with existing facilities and ongoing activities. Several aspects of
the single-laboratory evaluation and the collaborative test bear this out. The
prescribed electrodeposition was not the one recommended by the laboratory
which had originally developed the method (Puphal 1972). It was a compromise
between our technique and theirs because we could not tool up to test the
method using their electrodeposition as specified. Our equipment and facili-
ties did not allow us to electroplate at as high an amperage as their procedure
required nor could we electroplate in a fume hood to exhaust the chlorine
evolved. The modifications were designed to make the method more available to
other laboratories and they worked well at our laboratory. Even so, three of
28
-------
the six collaborating laboratories found it necessary to electroplate at an
even lower amperage.
Willingness to follow prescribed operations was not limited to the elec-
trodeposition. The variations in the tracer calibration have been described
earlier. Two of the laboratories were strongly against running the procedure
routinely because of the tedium of the solvent extraction separations as well
as other operations not associated with calibration or electrodeposition.
A few comments must be made regarding the choice between using plutonium-
236 or plutonium-242 to trace the plutonium analysis. Laboratories have their
own preference for very good reason and should be allowed the option of their
choice. If a laboratory may unknowingly encounter levels of plutonium-239 high
enough to subsequently mask the plutonium-242 tracer peak, then a plutonium-236
tracer would be the obvious choice. For laboratories routinely analyzing for
low or near-background levels of plutonium-238, then a plutonium-242 tracer
would result in a lower risk of method failure. If plutonium-240 to plutonium-
239 ratios are to be determined by mass spectrometry to obtain information
regarding the source of plutonium, then plutonium-242 would have to be used to
trace the plutonium analysis.
Consideration must also be given to the fact that only 6 of approximately
30 laboratories performing plutonium analyses participated in the collaborative
test and even these 6 did not follow the candidate method as specified. At
present the situation can be ascribed neither to the procedure nor to the
laboratories. In some instances, the procedure could not be implemented by the
prospective user laboratories. In other instances, the laboratories themselves
were hesitant to use techniques other than their own which they spent years
developing and making cost effective. Perhaps a second collaborative test,
already in progress, will aid in answering the question. This test will evalu-
ate an acid dissolution technique for the measurement of plutonium in soil.
The results of the completed collaborative study lend credence to an
alternate approach to that of proposing reference methods for achieving uni-
formity of results between laboratories in plutonium and other actinide anal-
yses. This alternate approach would be to set criteria on the final results
rather than on the method itself and to allow each individual laboratory to
use its own method. It would specify single-laboratory precision and bias
levels which a laboratory must demonstrate before its analytical results would
be acceptable. Each laboratory would then be required to qualify its method on
the basis of an effort similar to the collaborative test just described.
Additional criteria would also be set for a given analysis. These would in-
clude minimum yield, maximum counting error and quality of spectral resolution.
By allowing each laboratory to use its own method, all laboratories seriously
interested in performing actinide analysis, instead of a small percentage,
would become involved in similar collaborative studies. This would give a
realistic view of the true state of the art of such analyses among the labo-
ratories and would provide information regarding both potential problem areas
and exceptional approaches which could be shared by the scientific community.
29
-------
REFERENCES
Ostle, B. 1963. "Statistics in Research," 2nd Edition. Iowa State University
Press, Ames, Iowa. p. 93.
Puphal, K. W., and D. R. Olsen. 1972. "Electrodeposition of alpha-emitting
nuclides from a mixed oxalate-chloride electrolyte." Anal. Chem., ^f4_(2): 284-
289.
Sill, C. W. 1976. Private communication, Health Services Laboratory, ERDA,
Idaho Falls, Idaho.
VSill, C. W. 1975. "Some problems in measuring plutonium in the environment."
Proceedings of the Second Los Alamos Life Sciences Symposium, J. W. Healy,
Editor, Los Alamos, New Mexico - May 1974. Health Phys., _29_(4) : 619-626.
Sill, C. W., and F. D. Hindman. 1974a. "Preparation and testing of standard
soils containing known quantities of radionuclides." Anal. Chem., 46(1):113-
118.
Sill, C. W., K. W. Puphal, and F. D. Hindman. 1974b. "Simultaneous determi-
nation of aIpha-emitting nuclides of radium through californium in soil."
Anal. Chem., _46 (12) : 1725-1737.
Steiner, E. H. 1975. "Planning and Analysis of Results of Collaborative
Tests." Statistical Manual of the AOAC, Association of Official Analytical
Chemists, Washington, D.C.
Talvitie, N. A. 1972. "Electrodeposition of actinides for alpha spectrometric
determination." Anal. Chem., ^4(2):280-283.
Youden, W. J. 1975. "Statistical Techniques for Collaborative Tests,"
Statistical Manual of the AOAC, Association of Official Analytical Chemists,
Washington, D.C.
Youden, W. J. 1969. "The Sample, The Procedure, and The Laboratory," in
Precision Measurements and Calibration, H. H. Ku, Editor. National Bureau of
Standards Special Publication 300, Vol. 1, p. 142.
30
-------
APPENDIX
TENTATIVE METHOD FOR THE ANALYSIS
OF PLUTONIUM-239 AND PLUTONIUM-238 IN SOIL
(Fusion Technique)
Edited by
Erich W. Bretthauer, Paul B. Hahn,
Paulette B. Altringer, A. J. Cummings,
and Neil F. Mathews
Monitoring Systems Research and Development Division
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
The method described in this Appendix was distributed
to the participating laboratories for the interlaboratory
collaborative test.
-------
PREFACE
The analytical method described in this document is the proposed EPA
reference method for the measurement of plutonium in soil.
The method was selected on the basis of theoretical considerations by a
group of experts in the field of plutonium analysis. The method was then
subjected to intensive single-laboratory testing to determine precision,
accuracy, specificity, reliability, and interferences.
The method is proposed for collaborative testing to determine its suit-
ability as a reference method. Data from the collaborative tests will be used
to determine, on a statistical basis, the limits of error which can be expected
when the method is used by a typical group of analysts.
A-ii
-------
CONTENTS
Page
Preface A-iii
1. Scope and Application A-l
2. Summary A-2
3. Interferences A-2
4. Apparatus A-3
5. Standards, Acids, Reagents A-7
6. Calibration and Standardization A-9
7. Step-by-Step Procedure for Analysis A-14
8. Quality Assurance Program A-23
9. Calculation of Results A-26
10. Sample Calculations A-29
11. References A-32
Figure 1. Disposable electrodeposition cell and
support A-4
A-iii
-------
1. SCOPE AND APPLICATION
1.1 This method covers the analysis of soils for plutonium at levels greater
than 0.01 disintegrations per minute per gram (dpm/g) in all chemical and
physical forms known to exist in soils encountered in the United States. Such
universal applicability, however, can be guaranteed only in the event of com-
plete sample dissolution during the potassium fluoride and potassium pyrosul-
fate fusions.
1.2 The minimum detection level (MDL) of the method will depend on both the
background counting rate of the alpha spectrometer and the amount of plutonium-
238 and plutonium-239 contamination in the plutonium-236 tracer. Plutonium-236
having only a few hundredths percent of plutonium-238 and plutonium-239 con-
tamination is now commercially available and is recommended for this procedure.
For an analysis of 10 g of soil, employing 10 dpm of plutonium-236 tracer, a
1000-minute counting time on a spectrometer having a 17% counting efficiency
and a background of 0.010 counts per minute (cpm) over each energy region of
interest, and realizing an 80% plutonium recovery, the MDL is estimated to be
0.008 dpm/g.
1.3 The single-laboratory precision of the method at the 30- and 0.5-dpm/g
levels of plutonium has been demonstrated to approach that of counting statis-
tics alone. The accuracy of the method is expected to be within limits propa-
gated from counting statistics and the ±2% error associated with the prepara-
(8)
tion of a standard soil sample used to evaluate the method.
1.4 This method is recommended for use by experienced technicians under the
supervision of a radiochemist or other qualified person who fully understands
the concepts involved in the analysis and instrument calibrations. Further-
more, the method should be utilized only after satisfactory results are ob-
tained by the analyst in Section 8, "Quality Assurance Program" in which
A-l
-------
triplicate standard soil samples are analyzed.
2. SUMMARY
2.1 The principle of the analytical procedure follows. A known quantity of
plutonium-236 tracer is added to the sample which is decomposed completely by
a combination of potassium fluoride and pyrosulfate fusions with simultaneous
volatilization of hydrogen fluoride and silicon tetrafluoride. The fused cake
is dissolved in dilute hydrochloric acid and plutonium is precipitated with
barium sulfate. The barium sulfate is dissolved in acidic aluminum nitrate and
plutonium is extracted into a organic solvent. After scrubbing the organic
extract with nitric and hydrochloric acids, plutonium is stripped with per-
chloric-oxalic acid solution, electrodeposited and determined by alpha spec-
trometry. Sequential potassium fluoride and pyrosulfate fusions are known to
dissolve the most refractory and intractable plutonium compounds, allowing the
complete exchange between the tracer and the plutonium in the sample. The
chemical yield, counting efficiency, counting time, etc., are the same for all
plutonium isotopes which simplifies calculations. In addition to the activity
of plutonium-236 added and the weight of the sample, only the total number of
counts of plutonium-236, plutonium-239, and/or plutonium-238 recovered is
necessary to calculate the concentration of plutonium-239 and/or plutonium-238
in the sample.
3. INTERFERENCES
3.1 Reagents, glassware, and other sample processing hardware may cause con-
tamination. All of these materials must be demonstrated free from contami-
nation under the conditions of the analysis. Specific selection of reagents
and sample processing hardware is detailed in the procedure.
3.2 Possible procedural interferences are noted when apt to be encountered.
A-2
-------
4. APPARATUS (as described, or functionally equivalent)
4.1 INSTRUMENTATION AND ACCESSORIES
4.1.1 A windowless 2-rr gas flow proportional counter.
4.1.2 An alpha spectrometer capable of 40- to 50-kiloelectronvolt (keV)
resolution of actual samples electrodeposited on flat, mirror-finished stain-
less steel planchets with a counting efficiency greater than 17% and a back-
ground less than 0.010 cpm over each designated energy region. Resolution is
defined as the full width half maximum (FWHM) in keV, the distance between
those points on either side of the alpha peak where the count is equal to one-
half the maximum count.(1)
4.1.3 Disposable electrodeposition cells are constructed from 20-ml,
linear-polyethylene, liquid-scintillation vials. (See Figure 1.) A 1.59-
centimeter (cm) (5/8-inch) hole is cut in the bottom for introduction of the
(R)
anode. The foil-lined caps are replaced by 22-millimeter (mm) Polyseal caps
having a GCMI 400 thread design. The tubular portion of the polyethylene liner
is removed and the conical portion retained as a cover for the assembled cell.
A 0.36-cm (9/64-inch) hole having a beveled inside edge is bored through the
center of the cap. A 1.91-cm (3/4-inch) diameter washer with a 0.32-cm (1/8
inch) hole is cut from 0.08-cm (1/32-inch) neoprene and placed in the cap. The
shank of a hollow brass rivet (Dot Speedy Rivets, #BS4830, Carr Fastener Co.,
Cambridge, Mass.) is passed through the washer and cap to serve as an elec-
trical contact for the planchet cathode. (12)
4.1.3.1 The cathodes are 1.91-cm (3/4-inch) diameter, 0.38-mm (15
mil) thick, type 304 stainless-steel planchets pre-polished to a mirror finish.
The exposed cathode area is 2.3 square centimeters (cm2). Prior to use, the
planchets are degreased with detergent and/or acetone, immersed in hot concen-
trated nitric acid for 10 minutes, rinsed, and stored under distilled water
until needed.
4.1.3.2 The anode is a 1.27-cm (1/2-inch) diameter, 0.08-cm (1/32-
inch platinum or platinum-iridium disk having six 0.32-cm (1/8-inch)
registered trademark
A-3
-------
perforations and attached at the center to a 10-cm (4-inch) length of 0.16-cm
(1/16-inch) platinum or platinum-iridium rod.
4.1.3.3 To assemble the cell, the planchet is centered on the
threaded end of the cell and held in place by vacuum applied through one of the
holes of a two-hole rubber stopper butted against the other end. The cap
assembly is screwed on and leakage checked by adding water to the cell and ob-
serving the rise of air bubbles when the vacuum is reapplied. Flexing the cell
by alternately applying and releasing the vacuum improves the seal of leaky
cells. The combined resilience of planchet and washer maintains the liquid
seal and electrical contact during electrolysis.
V444444444 ANODE
SCINTILLATION
4444 VIAL
44444PLANCHET
444444 CAP
ASSEMBLY
4444 BASE
Figure 1. Disposable electrodeposition cell and support
4.1.3.4 Electrolysis is conducted without stirring, using an
electroplating unit such as a 10-volt, 5-ampere Sargent-Slomin Electrolytic
A-4
-------
Analyzer. The cell support and cathode socket consist of a non-insulating
banana jack attached to a Lucite® base.
4.2 LABORATORY EQUIPMENT
4.2.1 Comminution equipment.
4.2.1.1 Mortar and pestle - porcelain, with 275-ml capacity.
4.2.1.2 Pulverizer - Arthur H. Thomas 3367-D05 pulverizer, pulver-
izes 1-pound quartz ore 0.64 cm in diameter to 0.15 mm (100 mesh) in 1 minute,
requires 1-horsepower motor (optional).
4.2.2 Blender - Patterson-Kelly twin-shell blender, 4-liter capacity
(optional).
4.2.3 Balance - Mettler top-loading balance, capacity 1200 g, precision
±0.05 g.
4.2.4 Drying equipment.
4.2.4.1 Drying oven -maximum temperature >110° c, including trays
to fit.
4.2.4.2 Muffle furnace -maximum temperature >700° c.
4.2.4.3 Infrared drying lamp.
4.2.5 Temperature regulators.
4.2.5.1 Hot plate -capable of providing a temperature range of
10° C above ambient to 370° c.
4.2.5.2 Hot plate covered with asbestos cloth.
4.2.5.3 Fisher blast burner with a 4-cm grid - uses compressed air
with gas, capable of producing a temperature of approximately 1000° c.
4.2.5.4 Cold water bath -open variety with provision to cool a
platinum dish.
4.2.6 Shaker - mechanical, wrist action (optional).-
4.2.7 Set of U.S. Standard Sieves - 10 mesh (2.0-mm opening), 200 mesh
(74-ym opening) and 325 mesh (43-ym opening) (200 and 300 mesh sieves optional),
4.2.8 Centrifuge - capable of 2000 revolutions per minute (rpm) complete
with 40-ml heavy-walled centrifuge tubes.
4.2.9 pH meter with electrodes.
registered trademark
A-5
-------
4.3 LABWARE
4.3.1 Pipets.
4.3.1.1 Automatic pipets with disposable tips — optional sizes.
4.3.1.2 Measuring pipets, Mohr type — 10, 5, and 1 ml.
4.3.1.3 Pipets treated with silicone water repellent to eliminate
drainage and calibrated "to contain" by blowing residual liquid from the tip
- 1 ml.
4.3.2 Dropping bottles.
4.3.3 Beakers - 2000, 1000, 800, 150, and 100 ml.
4.3.4 Watch glasses -for 800-, 150-, and 100-ml beakers.
4.3.5 Graduated cylinders - 1000, 500, 100, 50, 25, and 10 ml.
4.3.6 Erlenmeyer flasks —250 ml graduated.
4.3.7 Separatory funnels - 2000 and 250 ml.
4.3.8 Volumetric flask - 50 ml.
4.3.9 Millipore filter holder - Pyrex" 47-mm filter holder apparatus.
4.3.10 Buchner filtering apparatus - 11-cm diameter.
4.3.11 Membrane filters -47-mm diameter, 0.45-ym-pore size, GA-6 cellu-
lose Metricel filters and DM-450 membrane filters.
4.3.12 Filter paper, glass fiber, Whatman -grade GFC.
4.3.13 Platinum dish - semi-flat reinforced bottom, 250 ml.
4.3.14 Polyethylene containers -screw cap, capacity for 300 g powder.
4.3.15 Polyethylene wash bottles -optional sizes.
4.3.16 Teflon® FEP bottles -optional sizes.
4.3.17 Safety glasses.
4.3.18 Ring-stand assembly —with nichrome triangle to accommodate 250-
ml semi-flat-bottomed platinum dish.
4.3.19 Tongs - platinum-tipped crucible type and test tube type.
4.3.20 Asbestos cloth — to cover hot plate and serve as pads, 0.16-cm
thick.
4.3.21 Boiling chips — silicon carbide, 8 mesh.
4.3.22 Timer - minute intervals.
4.3.23 Scissors.
4.3.24 Spatulas - optional sizes.
registered trademark
A-6
-------
4.3.25 Glazed paper sheets.
4.3.26 Disposable aluminum pans for use in muffle furnace.
4.3.27 Rubber policemen.
4.3.28 Glass stirring rods.
4.3.29 Glass bottle — screw cap, capacity for 2.5 liters.
4.3.30 Stainless-steel disks —to set under platinum dishes, 5-cm
(2-inch) diameter.
5. STANDARDS, ACIDS, REAGENTS
5.1 STANDARDS
5.1.1 National Bureau of Standards (NBS) americium-241 point source -
approximately 3 * 105 dpm, deposited on platinum and certified to ±1% of its
stated activity.
5.1.2 Plutonium-239 certified standard solution - approximately 5 x
dpm per ml of plutonium-239 in 2^1 nitric acid (available from Oak Ridge Na-
tional Laboratory) (optional).
5.1.3 Plutonium-236 solution -2.5 x 104 dpm of plutonium-236 in 2M
nitric acid in minimal solution (available from Oak Ridge National Laboratory).
5.1.4 Americium-241 solution - 1 x io5 dpm of americium-241 in 2N[ nitric
acid in minimal solution.
5.2 ACIDS
All solutions are made with distilled water. All acids are reagent grade
and meet American Chemical Society (ACS) specifications.
5.2.1 Hydrochloric acid - concentrated (12M), 10M, and 6M adjusted to
0.3M^ in sulfuric acid.
5.2.2 Hydrofluoric acid -concentrated (48% solution).
5.2.3 Nitric acid - concentrated (16N[), 8M, 4M, and 2M..
5.2.4 Oxalic acid — powder.
5.2.5 Perchloric acid -concentrated (72% solution).
5.2.6 Sulfuric acid -concentrated (18M), 1.8M, 0.9M, 0.18M, and 0.09M.
5.3 REAGENTS
All solutions are made with distilled water. All reagents listed are
A-7
-------
reagent grade and meet ACS specifications, unless otherwise defined.
5.3.1 Aliquat-336 (N03) -30% (by volume) in xylene.
Dissolve 300 ml of Aliquat-336, methyltricaprylyl ammonium chlo-
ride (General Mills, Inc., Kankakee, 111.), in 700 ml of xylene in a 2-liter
separatory funnel. Shake vigorously for 4 minutes with each of two successive
200-ml portions of 4^ nitric acid, draining and discarding the aqueous phase
each time. (This will convert the amine to the nitrate form.) Shake vigor-
ously for 4 minutes with each of three successive 300-ml portions of distilled
water, draining and discarding the aqueous phase each time. Allow final
moisture to settle out overnight. Draw the organic phase into a suitable
screw-capped, glass bottle for storage. °'
5.3.2 Aluminum nitrate, acidic - 2.2M.
Weigh 825 g of dry A1(N03)3*9H20 into a 2-liter beaker, add 450
ml of distilled water and warm until the salt dissolves. Add 85 ml of con-
centrated nitric acid and cool to room temperature. Filter the solution
through a well-washed DM-450 membrane filter in a Buchner' funnel. (This will
remove insoluble materials, particularly iron.) The density of this solution
should be 1.370 grams per ml at 25° c. (Pipet and weigh 1.00 ml of solution.)
If the density is not 1.370, add additional A1(N03)3-9H20 to produce this
density. (The number of grams of additional aluminum nitrate nonahydrate
required per liter of solution can be calculated by multiplying the difference
between the measured density and 1.370 by 4400.) Do not boil the solution or
loss of nitric acid will eventually result in hydrolysis of plutonium and a
decrease in both extraction efficiency and ability to dissolve barium sul-
fate.(10)
5.3.3 Ammonium hydroxide -concentrated (15M), 1.5M, and 0.15h1, free of
solid material.
5.3.4 Ammonium nitrate, anhydrous.
5.3.5 Ammonium sulfate, crystalline.
5.3.6 Barium chloride dihydrate - 0.45% solution.
5.3.7 Ceric sulfate.
5.3.8 Detergent.
5.3.9 Diethylenetriamine pentaacetic acid (DTPA).
5.3.10 Electrodeposition solution - l.OM (NH^SO,,, 0.013M NH2OH-HC1,
0.0033M DTPA, 0.01M H2C20.t, pH 3.5.
A-8
-------
Add 132 g of ammonium sulfate, 1.26 g of oxalic acid dihydrate and
0.90 g hydroxylamine hydrochloride to 900 ml of distilled water in a 2-liter
beaker and heat to dissolve. Dissolve 1.31 g of diethylenetriamine pentaacetic
acid (DTPA) in a minimum of 1:1 ammonium hydroxide with heating and add to the
main solution using a water rinse. (3.33 millimoles of the pentasodium salt of
DTPA in aqueous solution may be substituted.) Cool the solution to room tem-
perature and adjust the pH to 3.5 using concentrated sulfuric acid and a pH
meter to monitor the pH. Dilute the solution to 1 liter with distilled water.
5.3.11 Ethyl alcohol, alkaline.
Add a few drops of concentrated ammonium hydroxide to approximately
100 ml of ethyl alcohol.
5.3.12 Ferrous ammonium sulfate, hydrous.
5.3.13 Hydrogen peroxide — 30% solution.
5.3.14 Hydroxylamine hydrochloride.
5.3.15 Potassium fluoride, anhydrous.
5.3.16 Potassium hydrogen sulfate, crystalline.
5.3.17 Potassium nitrate, anhydrous.
5.3.18 Potassium metabisulfite — 25% solution.
5.3.19 Potassium sulfate, anhydrous.
5.3.20 Reprecipitating solution.
Dissolve 135 g of anydrous potassium sulfate in 915 ml of dis-
tilled water and 50 ml of concentrated hydrochloric acid with warming.(10)
5.3.21 Silicone water-repellent solution.
5.3.22 Sodium hydrogen sulfate, monohydrate.
5.3.23 Sodium sulfate, anhydrous.
5.3.24 Sodium nitrite - 25% solution.
5.3.25 Thymol blue, sodium salt - 0.02% solution.
5.3.26 Xylene.
6. CALIBRATION AND STANDARDIZATION
6.1 CALIBRATION OF THE 2n ALPHA COUNTER AND THE ALPHA SPECTROMETER.(10)
6.1.1 The window!ess, 2ir alpha counter is standardized by counting the
NBS americium-241 source to approximately 5 x io5 total counts.
A-9
-------
6.1.2 The efficiency of the 2ir alpha counter is calculated by dividing
the observed counts per minute (cpm) by the certified disintegrations per
minute (dpm) of the NBS americium-241 source.
6.1.3 Correct the counting efficiency for the difference in backscatter
between platinum and stainless steel by dividing the calculated efficiency
(from 6.1.2) by 1.023.(2'5)
6.1.4 Because a point-source standard electrodeposited on platinum (the
NBS americium-241 source) cannot be used to calibrate an alpha spectrometer
with an external detector for use with diffuse sources electrodeposited on
stainless steel, a secondary standard must be employed. Prepare a secondary
standard containing about 1 x 104 dpm of americium-241 electrodeposited on
stainless steel under the exact conditions subsequently described for electro-
deposition of samples.
6.1.5 Standardize the secondary standard by counting in the 2-n counter
until at least 2 x io5 counts have been collected.
6.1.6 Use the secondary standard to calibrate the alpha spectrometer and
to periodically check the initial calibration of both the spectrometer and the
2rr counter.
6.2 PURIFICATION OF THE PLUTONIUM-236 TRACER(6'11)
In order to accurately calibrate the plutonium-236 tracer by 2-n counting
and alpha spectrometry, it will be necessary to ensure the absence of plu-
tonium-236 daughters (uranium-232, thorium-228, radium-224, etc.) in the
tracer. The following purification must be performed just prior to the initial
calbiration and annually thereafter if additional calibrations are desired.
6.2.1 Mix 2.5 x 101* dpm of plutonium-236 with 3 g of anhydrous potassium
sulfate and 3 ml of concentrated sulfuric acid in a graduated 250-ml Erlenmeyer
flask.
6.2.2 Heat the flask on an uncovered hot plate at maximum temperature
until the sulfuric acid fumes and the potassium sulfate dissolves.
6.2.3 Heat the solution over a high-temperature blast burner while
swirling the flask continuously until a pyrosulfate fusion is obtained. Con-
tinue heating until the heavy fuming subsides and most of the excess acid has
been volatilized.
6.2.4 Cool the melt to room temperature and add 0.5 ml of concentrated
A-10
-------
sulfuric acid and 35 ml of distilled water.
6.2.5 Add 1 drop of 30% hydrogen peroxide and boil for 5 minutes on an
uncovered hot plate to oxidize uranium and to ensure complete reduction of
Plutonium.
6.2.6 Add 1 ml of a 0.45% barium chloride solution to the boiling solu-
tion at a rate of 1 drop every 2 seconds while swirling the flask continuously.
6.2.7 Boil the solution for an additional 1 minute and repeat the addi-
tion of another 1 ml of barium chloride solution by the same technique.
6.2.8 Boil the solution again for 1 minute and cool for 10 minutes in a
bath of cold running water.
6.2.9 Transfer the cold solution and precipitate to a 40-ml heavy-walled
centrifuge tube with small portions of distilled water to give a total volume
of 30 to 40 ml.
6.2.10 Centrifuge at approximately 2000 rpm for 5 minutes. Decant and
discard the supernate. Wash the barium sulfate precipitate with 5 ml of
0.09^ sulfuric acid; centrifuge and discard the supernate.
6.2.11 Add 1 ml of 72% perchloric acid to the centrifuge tube and heat
carefully over a blast burner with continuous swirling to dissolve the barium
sulfate without letting the solution bump.
6.2.12 Cool the solution for 1 minute and immediately add 25 ml of 8M
nitric acid and 1 ml of 25% sodium nitrite.
6.2.13 Transfer the solution to a 250-ml separatory funnel with another
25 ml of 8^1 nitric acid and extract for 2 minutes with 50 ml of 30% Aliquat-336
(N03) in xylene.
6.2.14 Scrub the organic extract for 1 minute with 50-ml of 10N[ hydro-
chloric acid, and discard the scrub. Repeat this step.
6.2.15 Strip the plutonium from the organic extract first with 50 ml of
solution containing 5 ml of 72% perchloric acid and 2 g of oxalic acid and then
with 25 ml of water. Transfer the strips to a 250-ml Erlenmeyer flask (pre-
ferably one made of Vycor" or quartz to avoid any leaching of non-volatile
materials).
6.2.16 Add 5 ml of concentrated nitric acid and evaporate the solution to
near dryness. Add nitric acid as necessary throughout the evaporation of
"registered trademark
A-ll
-------
perchloric acid (especially if the solution darkens) to ensure the smooth and
complete oxidation of any organic material. CAUTION: Wet ashing with per-
chloric acid can be extremely hazardous. It is mandatory that the analyst be
thoroughly familiar with these hazards as well as accepted safety practices.
6.2.17 Near the end of the evaporation, swirl the flask continuously over
a small flame from a blast burner until virtually all of the perchloric acid
has volatilized. Heat the walls of the flask gently to prevent any condensa-
tion of the perchloric acid fumes. Do not bake the residue. Remove the flask
from the burner just prior to complete dryness and allow the last of the acid
to evaporate from the heat in the glass itself.
6.2.18 Add 5 ml each of concentrated hydrochloric and nitric acids to the
flask and re-evaporate to about 2 ml on a hot plate.
6.2.19 Add 15 ml of concentrated nitric acid and boil down to about 5 ml
to ensure complete dissolution of the plutonium and complete oxidation of
chlorides as indicated by the absence of color or fumes of chlorine and/or
nitrogen oxides.
6.2.20 Cool, add 25 ml of water, and filter the solution through a DM-450
membrane filter. Wash the flask and filter with enough distilled water to give
a final volume of 50 ml.
6.2.21 Dilute aliquots of the ^500 dpm/ml stock solution with 2M nitric
acid to give concentrations desired for use. Store all tracers in tightly
capped Teflon FEP bottles.
6.3 STANDARDIZATION OF THE PLUTONIUM-236 TRACER (10)
6.3.1 Transfer a 1-ml aliquot of the purified plutonium-236 stock tracer
(^500 dpm/ml) in 2M nitric acid onto a stainless-steel planchet with a cali-
brated silicone-treated pipet and slowly evaporate to near dryness under an
infrared lamp to minimize any loss. Keep the activity in the center of the
planchet in an area limited to approximately 2 cm (3/4-inch) in diameter by
alternately adding the tracer a few drops at a time and evaporating. The
partially filled silicone-treated pipet can be placed on its side between
additions with no loss of solution. To ensure quantitative transfer of the
tracer, carefully blow out the last few drops with a rubber bulb.
registered trademark
A-12
-------
6.3.2 When the last of the tracer has been transferred to the planchet
and evaporated nearly to dryness, add 2 or 3 drops of concentrated nitric acid
to help keep the activity spread as uniformly as possible and evaporate to
complete dryness.
6.3.3 Heat the dry planchet over a blast burner just to the first dull
red glow. Then quickly lower the temperature by placing the planchet on a cold
steel surface to minimise oxidation of the plate.
6.3.4 Count in the 2ir alpha counter immediately after cooling to avoid
any possibility of absorbing water vapor from the air. Collect at least
5 * 104 counts for the standard to ensure adequate statistical precision.
6.3.5 Prepare and count a duplicate source by repeating steps 6.3.1
through 6.3.4.
6.3.6 The 2ir counting rate of the plutonium-236 sources must be cor-
rected by determining the fraction of the total alpha activity due to pluto-
nium-236.
6.3.6.1 Transfer 2 ml of the purified plutonium-236 tracer
(^500 dpm/ml) to a 250-ml Erlenmeyer flask and add 4 ml of a 5% solution of
sodium hydrogen sulfate monohydrate in 1:1 sulfuric acid.
6.3.6.2 Evaporate carefully on a hot plate to near dryness.
6.3.6.3 Treat and electrodeposit as described in steps 7.7.3
through 7.7.14.
6.3.6.4 Count the electroplated source on an alpha spectrometer to
250 minutes over an energy range of 3 to 8 MeV. Determine the fraction of the
total number of counts in the alpha spectrum that is due to plutonium-236 in
the source. This fraction is the correction factor to be applied to the
counting rate of the plutonium-236 evaporated source in the 2ir proportional
counter. NOTE: Prolonged and repeated counting of high-level plutonium-236
sources on the alpha spectrometer should be avoided to minimize daughter recoil
contamination of the alpha detector. Alternately, such contamination can be
virtually eliminated by leaving a small amount of air in the counting chamber
(9)
and applying a small negative potential to the source plate.
6.3.7 Calculate the activity concentration of the plutonium-236 tracer
(dpm plutonium-236 per ml) by multiplying the observed 2-n counting rates of the
evaporated sources by the correction factor and dividing by the 2ir counter
efficiency and the volume of tracer used to prepare the evaporated sources.
A-13
-------
7. STEP-BY-STEP PROCEDURE FOR ANALYSIS
7.1 PREPARATION OF SOIL FOR ANALYSIS(10)
7.1.1 Break up soil aggregates, and pull apart any topsoil plugs. Cut
up any large pieces of vegetation and combine with the major soil sample.
7.1.2 Oven dry the sample at 110° c for 24 hours and allow it to cool
for 2 hours.
7.1.3 Weigh the entire sample to +0.5%. Denote this weight as K.
7.1.4 If root mat is present, heat the entire sample in a disposable
aluminum foil pan in a muffle furnace at 400° c for 3 hours to char the organic
material.
7.1.5 Grind the sample lightly using a mortar and pestle, using just
enough pressure to break up the clods of soil but not enough to grind the small
pieces of rock and sand that are inevitably present.
7.1.6 Pass the soil through a 10-mesh (2.0-mm opening) sieve to remove
any large rocks.
7.1.7 Weigh the sample which passed through the 10-mesh sieve. Denote
this weight at L.
7.1.8 Transfer the sieved soil to a plastic bag or plastic bottle and
shake for a few minutes to ensure adequate mixing.
7.2 SAMPLE DECOMPOSITION(10)
7.2.1 Weigh a representative 10.0 ± 0.1 g of the prepared soil sample
and transfer into a dry 250-ml semi-flat-bottomed platinum dish.
7.2.2 Add concentrated nitric acid a few drops at a time to one edge of
the powder as fast as the frothing and vigor of the reaction will permit until
the entire sample is covered with acid and a free-flowing suspension is ob-
tained. Do not swirl or allow the solution to froth higher than about 2 cm
from the top of the dish.
7.2.3 Heat the solution gently on a covered hot plate until all vigorous
reaction and frothing has subsided.
7.2.3.1 If significant reaction persists, evaporate the slurry to
dryness, cool, and then add concentrated nitric acid to give a thin slurry.
7.2.4 If the activity is expected to be less than 1 dpm/g, or is
A-14
-------
unknown, add 10 dpm of the plutonium-236 working tracer. For higher levels,
add as much plutonium-236 tracer as the estimated activity of plutonium-239 or
plutonium-238 in the sample. The total volume of tracer added should not
exceed 5 ml.
7.2.5 Add 48% hydrofluoric acid carefully a few drops at a time with
intermittent heating until the vigorous reaction has subsided. CAUTION:
Hydrofluoric acid is an extremely hazardous liquid. Use gloves to avoid con-
tact with skin and work in a fume hood to avoid breathing vapors.
7.2.6 Carefully add an additional 10 ml of 48% hydrofluoric acid and
evaporate until all liquid disappears and the cake is just moist with acid.
(If allowed to bake, the residue sticks tightly to the bottom of the dish,
retarding subsequent dissolution and increasing corrosion of the dish in the
presence of phosphates. If the sample is particularly high in iron, rapid and
complete dissolution in the subsequent fluoride fusion is facilitated if some-
what more hydrofluoric acid is allowed to remain.)
7.2.7 Add 30 g of anhydrous potassium fljjpride (flux) and mix the sample
and flux with a glass stirring rod for a few seconds to give a coarse mixture.
7.2.8 Place the platinum dish on a m'chrome triangle on a ring stand
and carefully apply as much heat as possible, with a high-temperature blast
burner, until the contents have dissolved completely and a clear melt is
obtained. As necessary, swirl gently to dissolve the sample present on the
sides of the dish. (The supporting ring must be sufficiently large to ensure
even heating of the dish. Approximately 6 to 10 minutes will be required to
dissolve the contents completely. Moderate quantities of organic matter will
oxidize smoothly without special attention. Oxidation of larger quantities
will be facilitated by addition of 1 g of solid potassium nitrate, although
high-iron samples will then precipitate earlier in the melt.)
7.2.9 When the sample completely dissolves, heat the sides of the dish
so that any solidified flux melts and runs down into the bottom of the dish.
7.2.10 Remove the dish from the flame. As the melt begins to solidify,
swirl the dish gently to deposit the cake uniformly thin on the bottom and
sides of the dish up to about 2 cm from the top. (This facilitates its trans-
position and lessens deformation of the dish.)
7.2.11 Cool to room temperature. Slowly add 35 ml concentrated sulfuric
acid around the sides of the dish in small increments allowing the frothing to
A-15
-------
subside between each addition.
7.2.12 Place the dish on the covered hot plate, and heat gently until the
solution begins to froth. If necessary, remove from heat until the frothing
subsides. Be prepared to set the dish in a cold water bath to quench the
reaction rapidly if the frothing threatens to go over the top of the dish.
(Frothing is caused by the evolution of hydrogen fluoride and silicon tetra-
fluoride.)
7.2.13 Repeat step 7.2.12 as necessary/
7.2.14 When danger of frothing over is past, gently heat the dish - first
on the covered hot plate, then on a small stainless steel disk on an uncovered
hot plate. Keep the subsequent frothing to a minimum until the potassium
fluoride cake has been transposed to a slurry. A layer of solid salts builds
up on the sides of the dish, and most of the water and excess sulfuric acid are
driven off, leaving a slightly moist cake.
7.2.15 Gently heat the dish over the blast burner until the solids on the
sides melt and the last few small chunks of the main cake dissolve. (If the
transposition is carried out too rapidly and there are quite large chunks of
original potassium fluoride cake still present when the temperature is raised
over the blast burner to make the pyrosuUate fusion, hydrofluoric acid will be
driven out of the solution faster than the chunks of cake will dissolve and the
fluoride remaining will be insufficient to volatilize the last of the silica
completely. Consequently, the cake will not transpose completely to give a
clear pyrosulfate fusion in the following step.)
7.2.16 Add 20 g of anhydrous sodium sulfate. Heat carefully with a low
flame from the blast burner until the thick almost solid suspension changes to
a thin one that is easily boiled. As fast as boiling will permit, increase the
temperature until the entire sample has dissolved and a clear pyrosulfate
fusion is obtained. (Occasionally, if the transposition is performed a little
too fast, a slight scum of silica might be present on the surface of the melt
but will do no harm. Do not heat the pyrosulfate fusion any hotter or longer
than necessary to give a clear melt to minimize dissolution of platinum from
the dish.)
7.2.17 Remove the dish from the flame. When the melt starts to solidify,
swirl the dish gently to deposit the cake in a thick layer around the sides of
the dish. Allow the sample to cool to room temperature.
A-16
-------
7.2.18 Add 350 ml distilled water and 25 ml concentrated hydrochloric
acid to an 800-ml beaker and heat to boiling on an uncovered hot plate.
7.2.19 As soon as the solution begins to boil, flex the sides of the
platinum dish gently to break the cake loose and carefully empty the contents
into the hot solution.
7.2.20 Continue to heat the solution and cake as rapidly as possible on
the uncovered hot plate with continuous stirring. (This will prevent severe
bumping and ensure the immediate dissolution of the calcium sulfate cake as it
disintegrates. Calcium sulfate becomes distinctly less soluble in dilute acid
the longer it is allowed to stand in the crystalline state.)
7.2.20.1 If the calcium sulfate dissolves completely, or only a
slight turbidity remains, add 50 ml of water.
7.2.20.2 If the calcium sulfate does not dissolve completely, add
minimal amounts of concentrated hydrochloric acid until the turbidity de- g$^>-
creases. A maximum of 50 ml more may be added in this step. Further boiling -If 4>~
should yield an essentially transparent solution in a few minutes. Add dis- f1--
tilled water until the total volume of additional added concentrated hydro-
chloric acid and distilled water is 50 ml.
7.2.20.3 In the unusual event that the solution does not clear up
sufficiently with the additional 50 ml of concentrated hydrochloric acid,
transfer the solution to a 2-liter beaker with 375 ml of distilled water and
heat to dissolve the remaining calcium sulfate, adding up to an additional 75
ml of concentrated hydrochloric acid and/or distilled water as necessary. If
calcium sulfate still remains undissolved, add another 375 ml of distilled
water and up to another 75-ml portion of concentrated hydrochloric acid and
continue heating. (This should dissolve a sample containing as much as 3.2 g
of calcium in 10 grams of soil.) Add 70 g of solid potassium hydrogen sulfate
to the hot solution for each additional 375-ml portion of water used in this
step to dissolve the sample (i.e., 70 g for one addition, 140 g for two).
7.2.21 Add 5) ml of 25% potassium metabisulfite and a couple of 8-mesh
silicon carbide boiling chips to the solution from step 7.2.20.1, 7.2.20.2, or
7.2.20.3.
7.2.22 Cover the beaker with a watch glass and boil the solution for 10
to 15 minutes to hydrolyze condensed phosphates and to ensure complete reduc-
tion of plutonium to the quadrivalent state. Proceed with precipitation of
barium sulfate.
A-17
-------
7.3 BARIUM SULFATE PRECIPITATION (7'10'i;L)
7.3.1 Remove the watch glass momentarily and add 5 ml of a 0.45% solu-
tion of barium chloride dihydrate to the boiling solution from a 5-ml Mohr
pipet in about 0.5-ml increments every 3 seconds while stirring the solution
vigorously and continuously with a stirring rod.
7.3.2 Replace the watch glass and continue boiling the solution for 1
minute.
7.3.3 Repeat the addition of 5-ml portions of the barium chloride solu-
tion followed by a 1-minute boiling period five more times until a total of 30
ml of the 0.45% barium solution has been added.
7.3.4 Filter the hot solution through a 47-mm GA-6 Metricel filter in .
I ' i • i )
the filtering chimney. l^/v--1-^ ' *
7.3.5 Rinse the beaker and the precipitate with 0^09M sulfufic acid
delivered from a polyethylene wash bottle. Do not transfer the boiling chips.
7.3.6 Discard the filtrate and wash solution.
U , M -
-v^ w -i •• '
7.4 REPRECIPITATION OF BARIUM SULFATE ''' *V ^ w-'
7.4.1 Place the 6A-6 Metricel filter containing the barium sulfate into
a 250-ml Erlenmeyer flask and add 4 ml concentrated sulfuric acid and 3 drops
concentrated nitric acid.
7.4.2 Heat the solution on a covered hot plate until the sulfuric acid
fumes and then more strongly over a blast burner until the barium sulfate has
dissolved completely and the brown color from the filter has been destroyed.
If necessary, add an additional 1 ml of concentrated sulfuric acid to obtain
complete dissolution. ([to not permit evaporation of any significant quantity
of sulfuric acid or part of the barium sulfate will reprecipitate in a high-
temperature modification that is not readily soluble in the subsequent aluminum
nitrate dissolution. Subsequently, the barium sulfate particles will become
coated with the water- immiscible organic solvent in the extraction process and
will transfer to the organic phase giving a pseudo-extraction effect.)
7.4.3 Add 1 drop of a 1:1 mixture of concentrated nitric and 72% per-
chloric acids to the hot solution to oxidize the last of the organic matter.
7.4.4 Immediately set the flask off to cool to room temperature.
7.4.5 After the flask has cooled, add 60 ml of the reprecipitating
solution and 1 ml of 25% potassium metabisulfite.
A- 18
-------
7.4.6 Set the flask on the uncovered hot plate.
7.4.7 When the cake has disintegrated, add 1 ml of a filtered 20% solu-
tion of ferrous ammonium sulfate in 0.9M^ sulfuric acid and boil the solution
for 2 minutes. (This will complete the reduction of hexavalent plutonium that
will have been produced in the perchloric acid oxidation.)
7.4.8 Filter the barium sulfate while still hot on another GA-6 Metricel
filter and wash with a few milliliters of 0.09M sulfuric acid.
7.4.9 Discard the filtrate and wash solution.
7.5 DISSOLUTION OF BARIUM SULFATE(10)
7.5.1 Place the filter containing the barium sulfate in a 250-ml Erlen-
meyer flask.
7.5.2 Add 2 ml of concentrated nitric acid and 4 ml of 72% perchloric
acid. CAUTION: Wet ashing organic material with perchloric acid can be ex-
tremely hazardous. It is mandatory that the analyst be thoroughly familiar
with these hazards and accepted safety precautions.
7.5.3 Heat the flask on a hot plate until the refluxing perchloric acid
reaches the top of the flask. (By this time, the filter will have been oxi-
dized and the barium sulfate will have been dissolved completely. Certain soil
samples, however, may not clear up completely because of the presence of other
elements, but any remaining precipitate will dissolve subsequently in the
aluminum nitrate. Longer boiling with perchloric acid should be avoided be-
cause of increased oxidation of both cerium and plutonium in the sample, making
complete reduction by sodium nitrite more difficult. If not reduced subse-
quently, quadrivalent cerium carries through the extraction and causes severe
interference in the electrodeposition, and the recovery of plutonium is less
complete.)
7.5.4 Remove the flask from the hot plate for 1 minute.
7.5.5 Combine 50 ml of the acidic 2.2N[ aluminum nitrate solution and 1
ml of 25% sodium nitrite solution and pour into the flask rapidly while swirl-
ing the flask continuously.
7.5.6 Heat the solution just to the boiling point. (This will redis-
solve any traces of barium sulfate that might have reprecipitated.)
7.5.7 Allow the solution to cool to room temperature.
A-19
-------
7.6 EXTRACTION OF PLUTONIUM(10)
7.6.1 Organic extraction of plutonium.
7.6.1.1 Pour th&rsolution into a 250-ml separatory funnel and add
50 ml of 302 AlJ^aJ^aa^^NOg) in xylene.
7.6.T.^ Rinse the walls of the flask with 25 ml of the 2.2|1 acidic
aluminum nitrate solution and add 5 ml of 25% sodium nitrite.
7.6.1.3 Transfer the rinse to the separatory funnel, and swirl the
separatory funnel just enough to distribute the blue color of the nitrous acid
through the aqueous phase and allow to stand for 2 minutes.
7.6.1.4 Shake vigorously for 3 minutes, preferably on a mechanical
shaker, but not hard enough to cause formation of stable emulsions.
7.6.1.5 Allow the solution to stand for 10 minutes.
7.6.1.6 Discard the aqueous phase.
7.6.1.7 Swirl the separatory funnel and let the solution stand for
another 2 minutes.
7.6.1.8 Discard the additional aqueous phase that separates due to
drainage. (This will ensure maximum elimination of the large quantity of
barium and aluminum present.)
v/7.6.2 First acid scrub of the organic phase to strip the tervalent ac-
tinides and lanthanides.
7.6.2.1 Shake for 2 minutes with three successive 10-ml portions of
8M nitric acid. After each of the three scrubs, allow the phases to separate
for 2 minutes and drain and discard the lower aqueous layer. (This will remove
the last traces of barium, aluminum, tervalent actinides and lanthanides,
particularly cerium.)
7.6.3 Second acid scrub of the organic phase to strip thorium.
7.6.3.1 Shake for 3 minutes with three successive 50-ml portions of
10M hydrochloric acid. After each scrub allow the phases to separate for 2 to
3 minutes and drain and discard the lower aqueous layer. If levels of thorium
higher than normal are present in the soil (>130 yg/10g), increase the number
of hydrochloric acid scrubs. 1^
7,6.4 Acid extraction of plutonium. ^
7.6.4.1 Shake vigorously for 2 minutes with 50 ml of a solution
containing 5 ml of 72* perchloric acid and 2 g of oxalic acid.
7.6.4.2 Allow to stand for at least 2 minutes for adequate phase
separation.
A-20
-------
x/-7
-------
further adjustment. (Three drops of thymol blue indicator added to the solu-
tion in the cell should yield a definite reddish-pink color. If the solution
has a straw-yellow hue add 1.8M sulfuric acid dropwise to a definite reddish-
pink end point.)
7.7.6 Lower the platinum anode into the solution until the bottom edge
of the anode is about 2 mm above the shoulder of the cell. (If set too deeply,
gas bubbles will be trapped and cause fluctuation of the current.)
7.7.7 Turn on the current and adjust to 1.2 amps.
7.7.7.1 As the solution warms the current will increase and must be
readjusted to 1.2 amps when it rises above this value.
7.7.7.2 After 15 to 30 minutes the current will stabilize and elec-
trolysis can be allowed to continue at 1.2 amps without attention for a total
electrolysis time of 1.5 to 2.0 hours.
7.7.8 Without cutting off the current, add 10 ml of 1.5M ammonium hy-
droxide and continue the electrolysis for 1 minute.
7.7.9 Lift the anode out of the cell and then switch off the current.
7.7.10 Discard the solution in the cell.
7.7.11 Rapidly flood the cell three times with a solution of 1% ammonium
nitrate in 0.15M ammonium hydroxide.
7.7.12 Disassemble the cell.
7.7.13 Quickly wash the planchet with a stream of alkaline ethyl alcohol.
Touch a piece of filter paper to the edge of the planchet to absorb the film of
alcohol.
7.7.14 Write the sample number on the bottom of the planchet. Place the
planchet in a cupped planchet and heat for 10 minutes on an uncovered hot
plate.
7.7.15 Count the sample in an alpha spectrometer to resolve the isotopes
of plutonium. For samples containing less than 1 dpm/g of plutonium a minimum
of 1.5 * 103 counts should be collected for the plutonium-236 tracer. For
higher levels, count for 1000 minutes or until 101* counts have been collected
in each of the plutonium-236 and the plutonium-239 and/or plutonium-238 energy
regions.
NOTE: Protactinium-231 quantitatively follows plutonium through this procedure
and if it is present in the soil its peak will be found at 100 to 130 keV lower
energy than the plutonium-239 peak in the alpha spectrum. Under normal
A-22
-------
conditions these peaks should be completely resolved. If not, graphically plot
the two peaks and resolve by extrapolation.
8. QUALITY ASSURANCE PROGRAM
For any analytical procedure, a rigorous quality assurance program must be
followed to ensure accurate and precise results. Such a program must include
the evaluation of all variables in the final calculation for their degrees of
uncertainty and for any significant systematic errors. Precautions must be
taken to eliminate any cross contamination between samples, especially if high-
and low-level samples are run concurrently. Standard samples should be ana-
lyzed both to check out initial capabilities and to provide for a continuing
quality control program.
8.1 The internal laboratory precision of the method is evaluated by consid-
ering the uncertainties in all the variables in the final calculation. These
include the counting uncertainties associated with counting the sample and the
standards for calibration, uncertainties associated with pipettings and tracer
dilutions and weighing the original sample, and any uncertainty in the timing
of the 2TT count during the calibrations. All uncertainties should be evaluated
and, if significant, propagated to the final result. Variability between labo-
ratories is expected to be greater than that for a single laboratory due to the
variability in NBS standards used for calibration, slight differences in cali-
bration procedures, etc. The interlaboratory precision of the method can be
adequately estimated only on the basis of collaborative testing. Systematic
errors in the method will be minimized by calibrating all pipets, volumetric
flasks, and balances used for the tracer calibration and sample analysis, and
by calibrating the 2ir counter timing mechanism. The systematic error intro-
duced by the ±1% uncertainty in the NBS standard and the error in the back-
scatter correction factor cannot be compensated for.
8.2 Cross contamination of samples may be avoided with good housekeeping and
by either segregating apparatus used for high- and low-level samples, or by
carefully decontaminating glassware and platinumware between analyses.
A-23
-------
Contamination of stock reagents must be avoided. This can best be accomplished
by employing intermediate containers to which small portions of the stock
reagents can be transferred before adding to the sample. The excess reagent is
then discarded and the intermediate container rinsed before reuse. Reagent
blanks using the same reagents, tracer, glassware, platinumware, electrodeposi-
tion equipment and detector must be run initially and periodically thereafter
to determine the radiochemical background for the method and ascertain that
contamination of these items has not occurred.
8.3 PREPARATION OF STANDARD SOILS(8)(optional)
Standard soil samples prepared as outlined below should be analyzed in
triplicate to evaluate the initial capabilities of a laboratory and periodi-
cally thereafter to provide for a continuing quality control program.
8.3.1 From the desired geographical area, select two or three times as
much soil (approximately 5400 g) as the total quantity of standards to be pre-
pared. Dry for 24 hours at about 110° c.
8.3.2 Grind the sample lightly in a mortar and pestle, using just
enough pressure to break up the clods of soil but not enough to grind the small
pieces of rock and sand that are inevitably present.
8.3.3 Heat the entire sample in a disposable aluminum foil pan in a
muffle furnace at 400° c for 3 hours to oxidize organic material.
8.3.4 Sieve using a 200-mesh (74-ym opening) U.S. Standard Sieve. Dis-
card the rocky residue not passing through the sieve.
8.3.5 Blend the entire batch of prepared soil overnight.
8.3.6 Resieve about 600 g of the -200-mesh stock soil through a combi-
nation of 200-mesh and 325-mesh (44-yrn opening) sieves until about nine tenths
of the material has passed a second time through the 200-mesh sieve. (This is
to ensure absence of larger or irregular particles to facilitate resieving of
the final spiked material.)
8.3.7 Remove the 200-mesh sieve and continue shaking the 325-mesh sieve
until little more of the fine material passes through.
8.3.8 Place approximately 100 g of the -200, +325-mesh fraction into a
250-ml platinum dish. Combine and save the remaining fractions of the 600 g
of -200-mesh stock soil in the two screens and pan.
8.3.9 Add small portions of distilled water to the soil in the platinum
A-24
-------
dish and stir thoroughly until a smooth paste is obtained.
8.3.10 Add 1 ml of a standard solution containing about 5 x 10^ dpm/ml of
plutonium-239 in 2M nitric acid dropwise with continuous stirring from a
calibrated silicone-treated pipet. Mix each drop of the radioactive solution
thoroughly throughout the wet soil with a heavy glass stirring rod before
adding the next drop.
8.3.11 Heat the mud under an infrared lamp while stirring thoroughly and
continuously until the mass becomes immobile. (This is to prevent separation
of any liquid phase that could evaporate to form areas of higher concentrations
or "hot spots" of activity.) Break the soil into small pieces with the stir-
ring rod. Save the soil clinging to the stirring rod and any escaping soil
particles for the subsequent determination of plutonium-239 losses.
8.3.12 Dry the sample at 110° c for several hours and then muffle the
sample at 700° c for 4 hours.
8.3.13 In the following grinding and screening operations, it is manda-
tory that all of the spiked soil be accounted for in order to make the neces-
sary correction for plutonium-239 losses. Perform these operations on a large
sheet of glazed paper to recover any lost soil. Take the necessary precautions
to avoid inhaling any radioactive dust or contaminating the laboratory area.
8.3.14 Grind the dried material with a mortar and pestle until it passes
entirely through the 200-mesh sieve. Collect the sieved material in the pan
provided with the sieve. (It will be necessary to tap the screen sharply
against the bench top to keep the sieve from glazing over with the fine powder
obtained on grinding.)
8.3.15 Add enough of the same unspiked -200-mesh stock soil to give a
total of 1800 ± 1 g and blend overnight to ensure homogeneity.
8.3.16 To determine the quantity of plutonium-239 activity not included
in the soil sample, quantitatively transfer all of the residual spiked soil
left on the stirring rod, mortar and pestle, screen pan and the glazed paper to
the residual material in the platinum dish used to prepare the spiked soil.
Use nitric and hydrofluoric acids, as well as a rubber policeman, if necessary,
to rinse the stirring rod and mortar and pestle. Rinse the screen and pan with
distilled water.
8.3.17 Add a few milliliters of 48% hydrofluoric acid and 500 dpm of
calibrated plutonium-236 working tracer to the platinum dish.
A-25
-------
8.3.18 Evaporate to dryness.
8.3.19 Analyze the residue as described in Section 7.
8.3.20 Subtract the activity remaining in the dish from the activity
added and divide by the total weight of the prepared soil.
8.3.21 When prepared as directed, the sample contains about 28 dpm/g of
plutonium-239. Smaller concentrations can be prepared either by using a
smaller quantity of the plutonium initially or by blending weighed quantities
of the higher standard with additional weighed quantities of the same -200-
mesh soil used to prepare the original standard. When samples are prepared
with concentrations below a few dpm/g, the soil should be obtained from at
least 2 feet below the surface of undisturbed ground to minimize corrections
that must be made for the radionuclides present from global fallout.
9. CALCULATION OF RESULTS (3/5)
9. 1 CALIBRATION OF THE 2n ALPHA COUNTER
9.1.1 The counting efficiency of the 2ir counter is determined by count
ing an NBS certified americium-241 source electrodeposited on a platinum disk.
9.1.2 The 2TT counting efficiency (E2ir) is calculated as:
(9-1-2)
2ir (ai)(t)(1.023)
in which Cx = the net counts of the americium-241 source
&i = the certified activity of the americium-241 source (dpm)
t = the duration of the count (min)
1.023 = the backscatter factor correcting the counting efficiency
of a source on platinum to that on stainless steel
9.2 STANDARDIZATION OF THE PLUTONIUM-236 TRACER
9.2.1 The purified plutonium-236 stock tracer is standardized by count-
ing evaporated sources on the 2v counter and an electrodeposited source on the
alpha spectrometer. The 2i\ count, which represents total activity, is cor-
rected by multiplying by the plutonium-236 fraction of the total activity as
determined by alpha spectrometry.
A- 26
-------
9.2.2 The activity concentration (AC in dpm plutonium-236 per ml) of the
stock tracer is calculated from:
(C21r)(f6)
AC =
(E^JTVHty ^'e~c>
in which C27T = the net counts of the evaporated source on the 2ir counter
E21T = the counting efficiency of the 2ir counter
v = the volume of stock tracer used to prepare the evaporated
source (ml)
t = the duration of the count for the evaporated source on the
2ir counter (min)
f6 = the ratio of the net counts in the plutonium-236 energy
region to the net counts in the entire 3 to 8 MeV energy
region in the alpha spectrum of the electroplated tracer
source
9.2.3 The plutonium-236 activity (T in dpm) added to the sample to trace
the plutonium recovery through the analysis is calculated as:
T = (AC)(D)(V)(e-U) (9.2.3)
in which AC = the activity concentration of the stock tracer solution
(dpm plutonium-236 per ml)
D = the dilution factor in preparing the working tracer from
the stock tracer
V = the volume of working tracer added to the sample (ml)
e~x = the decay correction for plutonium-236 for the time
interval between tht date of tracer calibration and date
of sample analysis
9.3 CALCULATION OF PLUTONIUM CONCENTRATIONS IN THE ALIQUOT OF SOIL TAKEN FOR
ANALYSIS
9.3.1 The concentration of plutonium-239 or plutonium-238 in the aliquot
of soil taken for analysis (Xi in dpm/g) is calculated from:
X, =
M ' (C6)(W)
A-27
-------
in which C. = the net sample counts in the plutonium-239 or plutonium-238
energy region of the alpha spectrometer
C6 = the net sample counts in the plutonium-236 energy region of
the alpha spectrometer
T = the activity of plutonium-236 tracer added to the sample (dpm)
W = the weight of the soil aliquot taken for analysis (g)
9.3.2 The above calculation assumes that the plutonium-236 tracer used
in the analysis is sufficiently free from plutonium-238 and plutonium-239
activities (<0. 1%) to cause negligible interference in the plutonium determi-
nations. Older supplies of plutonium-236 (pre-1974) may contain appreciable
amounts of plutonium-238 and/or plutonium-239 (up to 1% or 2%) and should not
be used. If the poorer grade tracer is used, a freshly purified portion must
be assayed for plutonium-236, plutonium-238, and plutonium-239 by alpha spec-
trometry and the necessary corrections for adding plutonium-238 and plutonium-
239 to the sample with the tracer must be made.
9.4 CALIBRATION OF THE ALPHA SPECTROMETER AND CALCULATION OF THE PLUTONIUM
RECOVERY
9.4.1 The absolute counting efficiency of the alpha spectrometer (E )
must be determined in order to evaluate the plutonium recovery through the
analytical procedure. Americium-241 electroplated in the same manner as the
samples should be used for this purpose. The spectrometer counting efficiency
may be calculated from:
(rs)(E2J
E_ = —5- - (9.4.1)
s
in which r = the net counting rate of the electroplated source over the
entire energy region on the alpha spectrometer (cpm)
r27r = the net counting rate of the same source on the 2ir counter
(cpm)
E2ir = the counting efficiency of the 2ir counter
9.4.2 The plutonium recovery through the analysis (Y) is calculated
from:
A-28
-------
Y - - (9.4.2)
in whi'ch Rg = the net counting rate in the plutonium-236 energy region of
the alpha spectrum of the sample (cpm)
9.5 PROPAGATION OF UNCERTAINTIES
9.5.1 The uncertainties associated with the plutonium-236 tracer cali-
bration and the soil analysis are estimated from the 2o or 95% confidence level
(95% C.L.) uncertainties of all appropriate radioactivity counts, weighings,
pipettings, dilutions and measurements of counting times.
9.5.2 The 2a or 95% C.L. uncertainty in a net radioactivity count,
C = G - B, is:
in which G = the gross number of counts collected
B = the expected number of background counts during the same
time interval
The uncertainties in the other variables are determined experimentally by
replicate calibrations.
9.5.3 For linear addition or subtraction of independent variables, un-
certainties are propagated by taking the square root of the sum of the squares
of the individual uncertainties.
9.5.4 For linear multiplication and division of independent variables,
the fractional uncertainty in the final result is obtained by taking the square
root of the sum of the squares of the fractional errors in each of the inde-
pendent variables.
10. SAMPLE CALCULATIONS
10.1 CALIBRATION OF THE 2n ALPHA COUNTER
10.1.1 The NBS certified americium-241 standard (3.23 x 105 dpm ± 1%) was
counted on the 2ir alpha counter for 10.00 ± 0.02 minutes. The total number of
A-29
-------
counts collected was 1,564,612 ± 2,500 at the 95% C.L. (2a).
10.1.2 The 2ir counting efficiency calculated from equation 9.1.2 is:
P _ 1.564,612 ± 2,500*
t27r (3.23 x 105HUKOO ± 0.02)(1.023)
= 0.474 ± 0.001
10.2 STANDARDIZATION OF THE PLUTONIUM-236 TRACER
10.2.1 The first evaporated source of 1.029 ± 0.002 ml of the stock
plutonium-236 tracer gave 61,124 ± 494 net counts for a 250.0 ± 0.0 minute
count on the 2n counter. The electroplated tracer counted for 250 minutes on
the alpha spectrometer yielded 51,460 net counts in the plutonium-236 energy
region and 62 net counts in the rest of the 3 to 8 MeV energy region, giving a
correction factor (f6) of
51.460 , ,/ (51,460)(62)
51,460 + 62 - ^V(51,460 + 62)3
or 0.999 ± 0.000 to be applied to the 2i\ count.(5)
10.2.2 The activity concentration (AC) of the plutonium-236 tracer cal-
culated from equation (9.2.2) is:
ft. _ (61,124 ± 494)(0.999 ± 0.000)
(0.474 ± 0.001)(1.029 ± 0.002)(250.0 ± 0.0)
= 501 ± 4 dpm plutonium-236 per ml at the 95% C.L.
10.2.3 The second evaporated source yielded an activity concentration
value of 495 ± 4 dpm plutonium-236 per ml.
10.2.4 Averaging the two values, the activity concentration of the stock
tracer is:
AC = 498 ± 3 dpm plutonium-236 per ml at the 95% C.L.
10.3 CALCULATION OF PLUTONIUM-239 AND PLUTONIUM-238 CONCENTRATION IN THE
ALIQUOT OF SOIL TAKEN FOR ANALYSIS
10.3.1 A 1.002 ± 0.002 ml aliquot of working plutonium-236 tracer (stock
tracer diluted 1.029 ± 0.002 to 49.8 ± 0.01) was added to 10.0 ± 0.1 g of
*To avoid confusion, experimentally observed values were not rounded off in
all equations. The calculated results, however, have been rounded off to the
appropriate number of significant figures for the given situation.
A-30
-------
the -10-mesh fraction of the soil sample and the analysis was performed 65 days
after the calibration of the stock tracer (e"At = 0.958). A 1134-minute
spectrometer count of the sample yielded the following data.
Gross Background Net Counts
Energy Region Counts Counts +2o
Plutonium-236 1953 10 1943 ± 89
Plutonium-239 1394 6 1388 ± 75
Plutonium-238 215 8 207 ± 30
10.3.2 The amount of plutonium-236 tracer added (T in dpm) is calculated from
equation (9.2.3).
T = (498 ± 3) (^g ± o'.Ol2) (L°°2 ± °-002)(°-958)
= 9.88 ± 0.07 dpm plutonium-236
10.3.3 The plutonium-239 and plutonium-238 concentrations in the -10-mesh
fraction taken for analysis are calculated from equation (9.3.1).
Y - (1388 ± 75)(9.88 ± 0.07)
*9 " (1943 ± 89)(10.0 ± 0.1)
= 0.71 ± 0.05 dpm plutonium-239 per g
Y - (207 ± 30)(9.88 ± 0.07
*8 (1943 ± 89)(10.0 ± 0.1
= 0.11 ± 0.02 dpm plutonium-238 per g
10.4 CALIBRATION OF THE ALPHA SPECTROMETER AND CALCULATION OF THE PLUTONIUM
RECOVERY
10.4.1 The electroplated americium-241 source (step 6.1.4) yielded
206,741 ± 909 net counts in the 3 to 8 MeV energy range for a 100.0 ±0.0
minute count on the alpha spectrometer. A 100.0 ± 0.0 minute count of the
same source on the 2ir counter yielded 465,093 ± 1,363 net counts.
10.4.2 The counting efficiency of the spectrometer (E$) is calculated
from equation (9.4.1).
(2067 ± 9)(0.474 ± 0.001)
-Ls ~ (4651 ± 14)
= 0.211 ± 0.001
A-31
-------
10.4.3 The plutonium recovery for the analysis of the soil sample calculated
from equation 9.4.2 is:
Y = (1943 ± 87}/1134
(9.88 ± 0.07)(0.211 ± 0.001)
= 0.82 ± 0.04
11. REFERENCES
1. Heath, R. L., Scintillation Spectrometry-Gamma Ray Spectrum Catalogue.
Phillips Petroleum Co., Idaho Falls, Idaho, Report IDO-16880-1. 1964.
2. Hutchinson, J. M. R., C. R. Naas, D. H. Walker, and W. B. Mann, "Back-
scattering of alpha particles from thick metal backings as a function
of atomic weight." Int. J. Appl. Rad-Lat. Isotopes, ^19:517-522. 1968.
3. Overman, R. T., and H. M. Clark. Radioisotope Techniques, McGraw-Hill,
New York, N. Y. p. 109, 1960.
4. Puphal, K. W., and D. R. Olsen, "Electrodeposition of alpha-emitting
nuclides from a mixed oxalate-chloride electrolyte." Anal. Chem.
44(2):284-289. February 1972.
5. Sill, C. W., private communication, Health Services Laboratory, U.S.
Atomic Energy Commission, Idaho Falls, Idaho. January 1975.
6. Sill, C. W., "Purification of radioactive tracers for use in high sensi-
tivity alpha spectrometry." Anal. Chem. 46:1426-1431. September 1974.
7. Sill, C. W., "Separation and radiochemical detemination of uranium and
the transuranium elements using barium sulfate." Health Phys. 17:89-107.
1969.
8. Sill, C. W., and F. D. Hindman. "Preparation and testing of standard
soils containing known quantities of radionuclides." Anal. Chem. 46J1):
113-118. January 1974.
9. Sill, C. W., and D. 6. Olson. "Sources and prevention of recoil contami-
nation of solid-state alpha detectors." Anal. Chem. 42j13):1596-1607.
November 1970.
10. Sill, C. W., K. W. Puphal, and F. D. Hindman. "Simultaneous determina-
tion of alpha-emitting nuclides of radium through californium in soil."
Anal. Chem. 46(12):1725-1737. October 1974.
11. Sill, C. W., and R. L. Williams. "Radiochemical determination of uranium
and the transuranium elements in process solutions and environmental
A-32
-------
samples." Anal. Chem. 4^(12}:1624-1632. October 1969.
12. Talvitie, N. A. "Electrodeposition of actinides for alpha spectrometric
determinations." Anal. Chem. 44(2):280-283. February 1972.
A-33
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-77-078
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
FUSION METHOD FOR THE MEASUREMENT OF PLUTONIUM IN SOIL:
Single-Laboratory Evaluation and Interlaboratory Col-
laborative Test
5. REPORT DATE
July 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
P. B. Hahn, E. W. Bretthauer, P. B. Altringer, and N. F
Mathews
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
10. PROGRAM ELEMENT NO.
EHE 625C (ABJ)
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency-Las Vegas, Nevada
Office of Research and Development
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
13. TYPE OF REPORT AND PERIOD COVERED
1/1/74—9/30/76
14. SPONSORING AGENCY CODE
EPA/600/07
IS. SUPPLEMENTARY NOTES
16. ABSTRACT
This report presents the results of a single-laboratory evaluation and an
interlaboratory collaborative test of a method for measuring plutonium in soil.
The method employs potassium fluoride and potassium pyrosulfate fusions to decompose
a 10-gram sample, barium sulfate precipitations, solvent extraction and electrodeposi-
tion to isolate the plutonium, and alpha spectrometry to measure the plutonium. The
method is appended to the report.
The single-laboratory evaluation demonstrated that the overall within-laboratory
precision of the method can approach the precision of nuclear counting statistics
alone. The interlaboratory collaborative test showed the coefficient variation
representing differences between laboratories to be approximately 10% for concentra-
tion levels exceeding 1 disintegration per minute per gram.
Also discussed are several problem areas associated with environmental actinide
analyses. These include the difficulties which may be anticipated in requiring
monitoring laboratories to adopt a specific complex method of this type. Suggestions
are presented for improving agreement between laboratories by establishing criteria
for analytical results rather than requiring specific methodology.
This report covers a period from January 1, 1974, to September 30, 1976,
and work was. complejtfid_as. oJLJJesembex.31, 1976.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Plutonium
Quantitative analysis
Quality assurance
b. IDENTIFIERS/OPEN ENDED TERMS
Soil
c. COS AT I Field/Group
07B, D
14D
3. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
21. NO. OF PAGES
76
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
------- |