United States
Environmental Protection
- 32 ''- '.
Environmental Monitoring
and Support Laboratory
PO Box 15027
Las Vegas NV 89114
EPA-60O 7-80-019
February 1980
Research and Development
Radiometric Method for
the Determination of
Uranium in Soil and Air

Interagency
Energy-Environment
Research
and Development
Program Report

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                   RESEARCH REPORTING SERIES

 Research reports of the Office of Research and Development, U.S. Environmental
 Protection Agency, have been grouped into nine series. These nine broad categories
 were established to facilitate further development and application of environmental
 technology.  Elimination of traditional grouping was consciously planned to foster
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       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
       8.  "Special" Reports
       9.  Miscellaneous Reports


 This  report  has  been assigned  to the INTERAGENCY ENERGY—ENVIRONMENT
 RESEARCH AND DEVELOPMENT series.  Reports in this series result from the effort
 funded under the 17-agency Federal Energy/Environment Research and Development
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This document is available to the public through the National Technical Information
Service, Springfield, Virginia 22161

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                                          EPA-600/7-80-019
                                          February 1980
             RADIOMETRIC METHOD FOR THE
      DETERMINATION OF URANIUM IN SOIL AND AIR:
          Single-Laboratory Evaluation and
         Interlaboratory Collaborative Study

                         by

    V. R. Casella, C. T. Bishop, and A. A. Glosby
    Environmental Assessment and Planning Section
                   Mound Facility
               Miamisburg, Ohio 45342

             Contract No. EPA-78-D-tf0143
                   Project Officer

                    Paul B. Hahn

Monitoring Systems Research and Development Division
  Environmental Monitoring and Support Laboratory
             Las Vegas, Nevada  89114
   ENVIRONMENTAL MONITORING AND  SUPPORT  LABORATORY
         OFFICE OF RESEARCH AND  DEVELOPMENT
        U. S. ENVIRONMENTAL PROTECTION AGENCY
              LAS VEGAS, NEVADA   89114

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                          DISCLAIMER

     This report has been reviewed by the Environmental Moni-
toring and Support Laboratory-Las Vegas,  U.  S.  Environmental
Protection Agency, and approved for publication.   Approval does
not signify that the contents necessarily reflect the views
and policies of the U. S. Environmental Protection Agency, nor
does mention of trade names or commercial products constitute
endorsement or recommendation for use.
                               11

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                           FOREWORD
     Protection of the environment requires effective regulatory
actions that are based on sound technical and scientific infor-
mation.  This information must include the quantitative descrip-
tion and linking of pollutant sources, transport mechanisms,
interactions, and resulting effects on man and his environment.
Because of the complexities involved,  assessment of specific
pollutants in the environment requires a total systems approach
that transcends the media of air, water, and land.  The Envi-
ronmental Monitoring and Support Laboratory-Las Vegas contributes
to the formation and enhancement of a sound integrated monitoring
data base for exposure assessment through programs designed to:

       develop and optimize systems and strategies for
       monitoring 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 study of a
method for measuring uranium in  soil and air.  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 studies also allow each partici-
pating laboratory to critically  evaluate its capabilities in
comparison with other laboratories and often document the need
for taking corrective action to  improve techniques.  For
further information, contact the Methods Development and
Analytical Support Branch, Monitoring Systems Research and
Development  Division, Environmental Monitoring and Support
Laboratory,  Las Vegas, Nevada.
                       George. ,Morgan
                           Director
        Environmental Monitoring and  Support Laboratory
                           Las Vegas
                               iii

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                           ABSTRACT

     Results of a single-laboratory evaluation and an inter-
laboratory collaborative study of a method for determining
uranium isotopes in soil and air samples are presented.   The
method is applicable to 10-gram soil samples and to both glass
fiber and polystyrene (Microsorban) air filter samples.   Sample
decomposition is accomplished with a nitric-hydrofluoric acid
dissolution.  After a solvent extraction step to remove most of
the iron present, the uranium is isolated by anion exchange
chromatography and electrodeposition.  Alpha spectrometry is
used to measure the uranium isotopes.

     Two soil samples,  a glass fiber air filter sample,  and a
polystyrene air filter sample were used to evaluate the method
for uranium concentrations ranging from a few tenths to about
one hundred disintegrations per minute per sample.   Tracer
recoveries for the single-laboratory evaluation averaged 73%,
while the tracer recoveries for the collaborative study averaged
66%.   Although the precision of the collaborative study results
did not approach counting statistics errors,  the measured uranium
concentrations for these samples agreed to within 5% of the
reference concentrations when the uranium concentration was
greater than one disintegration per minute per gram of soil or
one disintegration per minute per air filter.

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                           CONTENTS


FOREWORD	     iii

ABSTRACT	      iv

LIST OF TABLES	      vi

ACKNOWLEDGEMENTS	     vii

INTRODUCTION 	       1

SUMMARY	       2

CONCLUSIONS	       2

CRITERIA 	       3

CHOICE OF METHOD 	       4

PREPARATION OF REFERENCE MATERIALS 	       4

SINGLE-LABORATORY EVALUATION 	       5

INTERLABORATORY COLLABORATIVE STUDY	       8

DISCUSSION OF RESULTS	      14

REFERENCES	      21

APPENDIX 1:  Tentative Method for the Determination of
             Uranium Isotopes in Soil and Air Samples. .      23

APPENDIX 2:  .Collaborative Study Instructions -
             Uranium in Soil and Air	      43

APPENDIX 3:  Data on Uranium-232 Tracer	      44

APPENDIX 4:  Laboratories Participating in the
             Uranium in Soil and Air Collaborative
             Study	      45

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                        LIST OF TABLES


No.                                                        Page

 1.  Single-Laboratory Evaluation Concentrations
     and Recoveries for Sample 1 (Glass Fiber Filter)...   6

 2.  Single-Laboratory Evaluation Concentrations and
     Recoveries for Sample 2 (Reference Soil)	   6

 3.  Single-Laboratory Evaluation Concentrations and
     Recoveries for Sample 3 (Microsorban Filter)	   7

 4.  Single-Laboratory Evaluation Concentrations and
     Recoveries for Sample 4 (Diluted Pitchblende Ore)  .   .   7

 5.  Collaborative Study Results for Sample 1 (Glass
     Fiber Filter - Reference Concentration:  U-238
     =0.21 dpm/filter; U-234 =0.24 dpm/fliter;
     U-236 = 1.32 dpm/f ilter)	   9

 6.  Collaborative Study Results for Sample 2
     (Reference Soil - Reference Concentration:
     U-238 =1.91 dpm/gram; U-234 =2.77 dpm/gram;
     U-235 = 0.098 dpm/gram)	10

 7.  Collaborative Study Results for Sample 3
     (Microsorban Filter - Reference Concentration:
     U-238 = 22.7 dpm/filter; U-234 = 43.8 dpm/
     filter; 1.90 dpm/filter)	11

 8.  Collaborative Study Results for Sample 4
     (Diluted Pitchblende Ore:   U-238 = 20.54
     dpm/gram;  U-234 = 20.54 dpm/gram; U-235 =
     0.89 dpm/gram)	12

 9.  Summary of Results for Uranium-In-Soil and
     Air Collaborative Study	15

10.  t-Test for Systematic Errors in Collaborative
     Study Results	18
11.   Overall Standard Deviation of Collaborative
     Study Results and Standard Deviations
     Expected from Counting Statistics Errors	20
                              VI

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                       ACKNOWLEDGEMENTS

     The authors would like to thank all those individuals from
the participating laboratories involved in the collaborative
study (cf. Appendix 4).

     Several people at Mound Facility provided support for the
present study.  Thanks are due to Warren E. Sheehan, F. Keith
Tomlinson and Billy M. Farmer for providing the necessary sample-
counting services and the Charles A. Phillips, Paul E. Figgins
and Harold W. Kirby for helpful discussions and suggestions.

     Acknowledgement is also given to the following laboratories
which provided materials used in this study:  Environmental
Measurements Laboratory, New York, N. Y.;  Environmental Moni-
toring and Support Laboratory, U.S. EPA-Las Vegas, Nevada; and
the Radiological and Environmental Sciences Laboratory, Idaho
Falls, Idaho.

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                         INTRODUCTION

     With the increased operations of nuclear power plants and
with projections that even greater production of nuclear energy
will be necessary to meet future energy demands (Lee,  et al.,
1977), the determination of uranium in environmental samples
is becoming more important.  Production of nuclear energy
involves many processes which could be sources of unacceptable
releases of uranium or other radioactive materials into the
environment, including uranium mining, uranium milling, con-
version of uranium to uranium hexafluoride, enrichment, fuel
fabrication, reactor power plant operations and fuel reprocessing.
Additional sources of releases may also occur during transportation
and waste management of the radioactive materials.

     The objective of this study was to choose and evaluate a
method which could be recommended for measuring uranium isotopes
in environmental soil and air samples.  Fluorometric procedures
(ASTM, 1977a; Danielsson et al., 1973) are most commonly used
for the determination of small concentrations of natural uranium;
however, such measurements are only indicative of uranium-238 due
to its extremely low specific activity.  In many cases, uranium-
234 is not in equilibrium with uranium-238 in soils and ores
(Sill, 1977; NCRP, 1975), and environmental samples may be en-
riched in uranium-235.  The concentrations of these isotopes
should be measured.  Isotopic data are of considerable help in
understanding both biological and geological processes and are
also necessary to assess the lung dose resulting from exposure
to uranium-containing materials.

     In addition to being an isotopic method, the recommended
method would have to be applicable to a wide variety of soil
samples found in the United States and to air samples collected
on polystyrene or glass fiber filters.  The method would also
have to produce results of sufficient accuracy and precision,
be free from interferences, be cost-effective, and be applicable
for routine analyses.

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                             SUMMARY

     This  report presents  the results of a single-laboratory
 evaluation and  interlaboratory collaborative study of a
 candidate  method for  the determination of uranium in air and
 soil.  The method was chosen on  the basis of a literature
 search and a preliminary laboratory evaluation of currently
 available  methods.  Reference soil samples and both glass fiber
 and polystyrene air filter samples were analyzed in a single-
 laboratory evaluation done at Mound Facility to show that
 criteria previously established  for the method were met.  After
 the single-laboratory evaluation, a copy of the procedure
 (Appendix  I) and the reference samples were sent to fourteen
 other laboratories for analysis  by the present method.  Uranium-
 232 tracer which had been  standardized at Mound was also supplied
 to the laboratories so that all  laboratories would be using the
 same tracer.  Eight laboratories had submitted results after about
 a 7-month  period, and a statistical evaluation of the collaborative
 study was  carried out.
                          CONCLUSIONS

     The requirments set forth in the criteria for the method
 (defined in next section) were satisfied by the present pro-
cedure for the determination of uranium isotopes in soil and
air.  Chemical recoveries averaged 787o for the single-laboratory
evaluation at Mound and 66% for the multilaboratory collaborative
study.  Uranium activities in the range of a few tenths of a
disintegration per minute (dpm) were measured and,  when the
uranium concentrations were greater than one dpm per gram of
soil or one dpm per air filter, the average deviation from the
reference concentration was about 5%.  The relative standard
deviations of the collaborative results among the laboratories
averaged about 10% for concentration levels exceeding one dpm
per gram of soil or one dpm per filter.  Plutonium, americium,
polonium and thorium tracers (30 to 300 dpm) were used to show
that these elements did not interfere with the uranium analysis.

     The single-laboratory and interlaboratory evaluations showed
that the present method provides a relatively simple and accurate
means of determining uranium in soil and air samples.

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                           CRITERIA

     Criteria for the present method were established based on
a literature review of published methods for determining uranium
in soil and air samples and the environmental data obtained using
these methods.

     The criteria were as follows:

     1.  The method will be a radiometric method yielding
         isotopic information, rather than a chemical method
         giving only total uranium.

     2.  The method will be applicable to up to 10 grams of
         a wide variety of soil samples found in the U.S.
         and shall also be applicable to air samples collected
         on polystrene or glass fiber filters.

     3.  The method will be capable of determining highly
         insoluble forms of uranium.

     4.  The method will reflect cost effectiveness by
         emphasizing simplicity of equipment, reagents and
         procedures.

     5.  The chemical yield of the method will be 50% or
         better.

     6.  The sensitivity of the method with 10-gram soil
         samples or air filter samples will be 0.10 dpm/g
         or dpm/filter, respectively.

     7.  Plutonium, americium, polonium, and thorium tracers
         will be used in testing the method to give assurance
         that isotopes of these elements do not interfere
         with the uranium analysis.

     8.  The single-laboratory relative standard deviation of
         the method, not including  the counting statistics
         error, will be ^570 or better.

     9.  The accuracy of the method will be dependent upon
         the accuracy of the  tracer activity U-232, which
         is expected to be about 1.5%,  the accuracy in  the
         measurement of the amount  of  tracer added, and
         the counting errors.

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                       CHOICE OF METHOD

     Three methods are commonly used for the initial decomposi-
tion of environmental samples:  acid leach, acid dissolution,
and fusion.  Since the acid dissolution and fusion methods
provide more rigorous decomposition of the sample matrix than
the acid leach method, it was decided to omit the acid leach
method from further consideration.  A recent comparison of acid
dissolution and fusion methods for the analysis of plutonium in
soil (Whittaker and Grothaus, 1979) has strongly indicated that
the two methods are equivalent, even for highly refractory forms
of plutonium.  This study showed that the acid dissolution method
was less time-consuming and more economical than the fusion
method; therefore, an acid dissolution method, similar to that
used for the measurement of plutonium in soil (USAEC, 1974),
was chosen for the present method.

     A method for the measurement of uranium isotopes in water
has been recently developed at Mound Facility (Bishop et al,
1978) through an Interagency Agreement with the EPA's Environ-
mental Monitoring and Support Laboratory-Las Vegas (EMSL-LV).
Several of the analytical techniques used in the uranium-in-water
method were found to be applicable to the measurement of uranium
isotopes in soil and air samples.  After sample decomposition by
an acid dissolution procedure, the uranium could be concentrated
by coprecipitation with iron hydroxide and isolated by anion
exchange chromatography in a hydrochloric acid medium,  prior to
electrodeposition onto a stainless steel slide for alpha pulse
height analysis.   However,  soil and air samples usually contain
a great deal more iron than water samples,  making it necessary
to remove the bulk of this iron before the ion exchange separa-
tion to prevent overloading of the anion exchange column with
ferric ions.   Extracting the hydrochloric acid sample solution
with isopropyl ether (Morrison and Freiser, 1957) before passing
this solution through the ion exchange column was found to be an
effective way to remove most of the iron from the sample solution.
              PREPARATION OF REFERENCE MATERIALS

     Two air filters and two soil samples were prepared as
reference materials for the single-laboratory evaluation and
the collaborative study.  The first simulated air sample,
referred to as Sample 1, was prepared by pipeting 250 A of a

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diluted uranium-236 standard solution onto a 70-mm diameter glass
fiber filter and drying in an oven at 120°C.  Based on the stand-
ardization of the U-236 standard solution by the National Bureau
of Standards (NBS),  the activity deposited onto each prepared
filter was 1.33 dpm.   The uncertainty of the calibration of the
standard solution was reported by the NBS to be 0.94 percent.   A
second simulated air sample, referred to as Sample 3,  was pre-
pared by placing 40.0 mg of a standard diluted pitchblende ore
between the layers of a rectangular Microsorban filter (100 mm
x 125 mm) and sealing the filter in a plastic bag.  When these
samples were analyzed, both the plastic bag and the filter were
ignited to ensure that no sample would be lost by removing the
filter from the plastic bag.  The diluted pitchblende ore was
obtained from the EPA's EMSL-LV and had a uranium-238 concentra-
tion of about 560 dpm/g.  The diluted ore was prepared by the
Radiological and Environmental Services Laboratory, U. S. Depart-
ment of Energy, Idaho Falls, Idaho by diluting an extensively
characterized primary unaltered pitchblende ore in secular
equilibrium with a background soil (Sill, 1977).

     The first reference soil sample, referred to as Sample 2,
was blended at the EMSL-LV and analyzed by Mound and EMSL-LV.
Uranium concentrations of the isotopes U-238 and U-234 in dpm/g
were, respectively, 1.91 ± 0.06 and 2.78 ± 0.08 from Mound's
analyses and 1.89 ± 0.07 and 2.77 ± 0.05 from the analyses done
at EMSL-LV using their method.  The second reference soil sample,
referred to as Sample 4, was prepared by physically hand-mixing
2 grams of a standard pitchblende ore (Sill, 1977) with 100 grams
of a soil of a known uranium content, and then blending this
mixture with about 500 additional grams of the same soil.  The
blending was carried out in a Patterson/Kelly twinshell blender
for a total of about 96 hours.  The soil of known uranium content
was obtained from Environmental Measurements Laboratory, U. S.
DOE, New York, N. Y.  During the blending of the  soil, duplicate
5-gram samples were taken for analysis at approximately 30 hours,
48 hours and at the end of the sample period, and the measured
average concentrations of U-238 and U-234 in dpm/g for these
samples were, respectively, 20.30 and 20.14  (30 hrs), 20.81 and
20.51 (48 hrs), and 21.30 and 20.86  (96 hrs).
                 SINGLE-LABORATORY EVALUATION

     A single-laboratory evaluation of the present method was
performed at Mound Facility in order to determine if the
criteria that had been established for the method had been met
before proceeding with the interlaboratory collaborative study,
The reference materials described in the previous section were
used to evaluate the method, and the results of  the single-

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      TABLE 1.  SINGLE-LABORATORY  EVALUATION CONCENTRATIONS
                AND RECOVERIES  FOR SAMPLE 1 (Glass Fiber
                Filter)3
Sample
1A
IB
1C
ID
Avg.
Ref .
U-238
(dpm/ filter)
0.184
0.249
0.193
0.200
0.207 ± 0.029

U-234
(dpm/filter)
0.227
0.293
0.207
0.214
0.235 ± 0.039

U-236
(dpm/filter)
1.38
1.44
1.28
1.40
1.38 ± 0.07
1.32 ± 0.03
Recovery
%
93
101
85
77
89 ± 10


      TABLE 2.   SINGLE-LABORATORY EVALUATION CONCENTRATIONS
                AND RECOVERIES FOR  SAMPLE  2  (Reference Soil)


Sample
2A
2B
2C
2D
2E
2F
2G
2H
21
2J
2K
2L
Avg.
U-238
(dpm/ gram)
1.78
1.87
1.90
1.90
1.93
1.90
1.92
2.01
1.99
1.94
1.90
1.89
1.91 ± 0.06
U-234
(dpm/ gram)
2.69
2.66
2.81
2.76
2.77
2.83
2.64
2.86
2.89
2.79
2.81
2.76
2.77 ± 0.08
U-235
(dpm/ gram)
0.109
0.087
0.097
0.091
0.099
0.100
0.093
0.103
0.089
0.102
0.100
0.096
0.098 ± 0.007
Recovery
%
62
75
73
77
79
71
78
58
86
75
83
66
74 ± 8

aErrors  in Tables  1  through 4 represent one standard deviation.

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      TABLE  3.   SINGLE-LABORATORY EVALUATION  CONCENTRATIONS
                 AND RECOVERIES FOR SAMPLE  3  (Microsorban
                 Filter)
 Sample
t
  U-238
(dpm/filter)
   U-234
(dpm/filter)
  U-235
(dpm/filter)
 Rejected by ASTM test.
                                                           Recovery
3A
3B
3C
3D
3E
3F
3G
3H
31
Avg.
23.1
22.2
23.0
21.8
23.7
19.5
22.3
23.0
25.5
22.7 ± 1.6
48.5
41.4
47.5
40.3.
29. 2T
41.5
44.2
.40.2
46.5
43.8 ± 3.4
1.91
1.86
2.00
1.82,
1.48T
1.85
1.85
1.88
1.99
1.90 ± 0.07
91
67
91
89
86
86
77
90
83
84 ± 8

       TABLE 4.  SINGLE-LABORATORY EVALUATION CONCENTRATIONS
                 AND RECOVERIES FOR SAMPLE 4 (Diluted
                 Pitchblende  Ore)


Sample
4A
4B
4C
4D
4E
4F
Avg.
Ref .
U-238
(dpm/gram)
20.32
20.02
20.32
21.39
21.25
21.30
20.77 ± 0.61
20.54 ± 0.23
U-234
(dpm/gram)
20.39
19.86
19.90
21.20
20.92
20.77
20.51 ± 0.55
20.54 ± 0.23
U-235
(dpm/gram)
1.02
1.03
1.02
1.18
1.05,
1.42T
1.06 ± 0.07
0.89 ± 0.02
Recovery
%
88
42
88
25
80
70
66 ± 26


 Rejected by ASTM test.

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 laboratory evaluation of these samples  are summarized in  Tables
 1  through 4.   Reference  values for  Samples 1  and  4 were calculated
 from the  concentrations  of the standard materials used in the
 preparation of these  samples  and are given in Tables  1 and 4.
 Since reference values were not known for  Samples 2 and 3,  the
 average uranium concentrations determined  in  the  single-laboratory
 evaluation for these  samples  were used  as  reference concentrations
 in  the subsequent  collaborative study.   An ASTM-recommended criterion
 (ASTM 1977a),  which is discussed in  the next  section  of this report,
 was  used  for rejection of  outliers.

      Four duplicate analyses  were performed on a  soil sample of
 known uranium  concentration,  obtained from Environmental  Measure-
 ments Laboratory,  New York, to test  the present procedure for
 interferences  from other radionuclides.  The  following tracers
 were added for these  analyses:   Po-210  (87  dpm) and U-236 (10 dpm);
 Pu-236 (93 dpm), Am-241  (258  dpm) and U-236 (10 dpm);  Th-228
 (38  dpm)  and U-236 (10 dpm);  and for  one duplicate determination
 no  tracers were  added to ensure that  there  were no alpha  peaks in
 the  areas  of interest.  The final spectra  from these  analyses
 showed that no plutonium and  thorium  could  be  detected (<0.1%),
 while only very  small  peaks were observed  for  polonium (<0.370)
 and  americium  ( and the uranium tracer recovery
for each of the analyses.   Since Mound and EPA personnel decided
in previous studies (Bishop et  al., 1978, 1979) that determin-
ations which had chemical recoveries less than 2070 were unaccept-
able, data listed in these tables with such low recoveries were
rejected as questionable and omitted from further consideration.
Outliers were rejected on the basis of an ASTM-recommended
criterion for rejection (ASTM 1977b).
                               8

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VO
              TABLE  5.   COLLABORATIVE  STUDY  RESULTS FOR SAMPLE 1 (Glass Fiber Filter
                         -  Reference Concentration:   U-238 =0.21 dpm/filter;  U-234 =
                         0.24 dpm/filter; U-236 =1.32 dpm/filter)a

U-238b X" ± Si
X U-234b X ± Sn-
X" U-236b
X i Si X Recovery
Lab (dpm/filter) (dpm/filter) XRgf (dpm/filter) (dpm/filter) XRgf (dpm/filter) (dpm/filter) XRgf ?„
1 0.17*0.01 ---c
2 ~~~
, 0.14*0.03 n 17+n ns
J 0.21±0.04 U.I/-U.UD
, 0.70*0.07 , 7n+o ,nt
* 1.69±0.09 i-^u-u./u
5 ~~~
, 0.36*0.03 o o1+n n7
0 0.26*0.02 u.ji-u.u/
7 0.26±0.05 n 9o+n n,
' 0.20±0.03 u.zj-u.ut
8 0.075±0.023 n nsfi+n oo
8 0.041±0.014 °-058±0-02
0.81 0.10±0.01
1.18±0.18*
""" 0.51±0.07
n ftl 0.13±0.03 n 9s+n 10
°-81 0.38±0.05 0-"-0.18
,- -,, 0.66±0.07 -, , s+n fiqt
D' IL 1.6410.09 J-.u-u.D^
	
, ,0 0.4910.04 n /fl+o 10
L'48 0.3210.02 0.4010.12
, in 0.2010.05 n 7n+n nn
1>iu 0.2010.03 u.^u-u.uu
- 0 no 0.00710.007 Q 027+0 028
^ U'":° 0.04610.015 u-uz/-u-uze
0.42 1.3210.03
2.13 ""
, n, 1.2210.09
L'U^ 1.5010.10
, ?Q 0.7610.07
•^ 1.3H0.08
1.2310.04
1.1910.06
-, A7 1.2510.06
il&/ 1.3H0.05
n ft, 1.2810.12
U'8J 1.2010.08
n ,, 1.6010.14
Uliz 1.2410.10
1.00 80
17
51
1.3610.20 1.03 11
JO
1.0410.391" 0.79 g^
1. 2H0.03 0.92 8°
1.2810.04 0.97 7£
1.24±0.06 0.94 g°
1.4210.25 1.08 7g

     aWhere S. is the experimental (within laboratory)  standard deviation; X is the average of replicate
      results; and XR ^ is the reference concentration  (dpm/filter).   This also applies  to Tables 6 through 8,

      The error given here is the error associated with one-sigma counting statistics.   This statement
      also applies to Tables 6 through 8.

     °When only one uranium concentration was determined, or if one value was rejected,  no average or
      standard deviation is tabulated.  This also applies to Tables 6  through 8.

     *Rejected because uranium tracer recovery was less than 20%.

     Rejected by ASTM test.

-------
         TABLE 6.   COLLABORATIVE STUDY RESULTS FOR SAMPLE 2 (Reference Soil
                   - Reference Concentration:  U-238  =1.91 dpm/gram; U-234
                   =2.77 dpm/gram; U-235 = 0.098  dpm/gram)
Lab
1
2
3
4
5
6
7
8
U-238 X ± Si
(dpm/gram) (dpm/gram)
1.86±0.03 , 89. o Q4
1.92±0.03 I-**-"-"*
1.67±0.05 , Sfl+f) OQ
2.08±0.08 1-88*0.29
1.94±0.06 1 aa+0 oq
1.82±0.06 L-88±0-09
1.75±0.05 , 76+Q 0,
1.76 + 0.04 l-'°-u-UJ-
1.85 + 0.03 , R,+n n,
1.87±0.03 1-86±0.02
1.84+0.03 -, Rs + f) n?
1.86±0.03 i-8510-02
1.48±0.03f
1.72±0.08 . 97+Q ..
2.21±0.11 ^'-U--"
X U-234
XRef (dPm/gram)
0 nn 2.71+0.04
u'vy 2.75±0.03
q. 2.78±0.08
U'ya 2.96+0.10
n go 2.64±0.07
u'y° 2.68+0.09
„„ 2.52+0.06
u'y/ 2.53+0.06
0 9? 2.70+0.04
U'y/ 2.74+0.04
0 9? 2.65+0.04
u>y/ 2.68+0.04
0.78 2.27+0.05
l Q3 2.47+0.11
L-UJ 3.49+0.17
X ± Si X U-235 X + Si X Recovery
(dpm/gram) XRgf (dpm/gram) (dpm/gram) XRgf ?„
2.73±0.03 0.99 ""
2.87±0.13 1.04
2.66±0.03 0.96 Q' 110+0 ' 010 °-110±0-001 l-12
2.53+0.01 0.91 o 102+0 007 °-090±0-018 °-92
2.72+0.03 0.98 o'l03+o'o05 °-106±0-004 i-08
2.67±0.02 0.96 o'083+o'o05 °-076±0-011 ° • 78
	 0.80 0.072±0.005 --- 0.62
2.98+0.72 1.08 o'o89+o'oiO °-083±0-009 °-85
85
89
70
45
40
28
76
78
68
70
67
69
74
88
60

t
 Rejected by ASTM test.

-------
        TABLE  7.   COLLABORATIVE  STUDY RESULTS FOR  SAMPLE 3 (Microsorban  Filter
                   - Reference Concentration:  U-238  =  22.7 dpm/filter; U-234 =
                   43.8 dpm/filter;  1.90 dpm/filter)

U-238 X i Si
X
U-234
X + S-- X
U-2:
Lab (dpm/filter) (dpm/filter) XR ^ (dpm/filter) (dpm/filter) XR f (dpm/fi
i 22
1 21
9 23
24
3 22
J 24
/ 18
4 23
5 21
5 19
, 22
6 24
7 19
' 20
8 19
8 20
.2±0
.4 + 0
.2il
.9il
.7iO
.1 + 0
.7±0
.4iO
.6iO
.0±0
.4tO
.9+0
.2±0
.7 + 1
.9 + 2
.4+1
~2 21.810.6
.0
.5*
J 23.4H.O
.5 ,, 1+, ,
.6 ^J-.i-J.J
•3 20.3H.8
•5 9 T 7 + 1 Q
.4 23.7U.8
.5
.0*
.8*
.1
0.96 £2
31
1.02 39
i m 43
i-UJ 46
0.93 33
0.90 23
1.04 £5;
0.85 33^;
0 90 35'
0.90 33
.2
.1
.0
.7
.0
Q
Q
10
H
12
iO
iO
+ ?
.OiO
.7
4
,2
4
7
iO
10
11,
15.
il.
.4
.2
. 1*
.9
.8
;S
.6
!e
.9
.7*
,0*
,8
43.3H.3 0.99
n 71

2
. 2
38.917.1 0.69 J
31.3H0.9 0.72 ]_
43.9,3.1 1.00 };
1
1 .
0.77 ]_'
	
	
.1610.
.5810.
.50+0.
.8810.
.5010.
.02+0.
.9310.
,65iO.
71 + 0.
7410.
0310.
46iO.
J5 X + Si
.Iter) (dpm/filt
	

10 2.3710.30
10 1 69+Q 2?
11
06 l 26+Q 34
05
10 1 79+0 90
06 i./y-u-^u
11
20*
26*
13
X R
er) XRef
	

1.25
0.89
0.66
0.94
0.90
0.77
.ecovery
7»
99
107
34
17
31
17
73
70
30
72
1553
11

*Rejected because uranium tracer recovery was less than 20%.

-------
       TABLE  8.   COLLABORATIVE STUDY RESULTS  FOR SAMPLE 4  (Diluted Pitchblende
                  Ore:  U-238  = 20.54 dpm/gram;  U-234 = 20.54 dpm/gram; U-235 =
                  0.89 dpm/gram)

U-238 X + Si
Lab (dpm/gram) (dpm/gram)
, 22.00±0.24 ,, nrm ,,
1 19.99±0.21 zJ--uu-J--^
, 19.24±1.14*
z 21.74+0.63
3 |5;5£S;ff 21.60±0.88
4 10.91tO.42"
, 20.22+0.32
D 18.77±0.81*
6 20:49*0:25 20-17t0.46
7 16.43±0.30f
o 17. 68 ±2. 91*
0 21.14+2.48*
X U-234 X + Si
XRef (dPm/8rani) (dpm/gram)
, n9 21.36*0.23 9n ri+1 91
i-u/ 19.65±0.21 ^u^1-1'^1
, n, 20.39±1.20*
i'Ub 21.56±0.63
, ns 20.44+0.54 ,, ns+n R,
^^ 21.66iO.53 21'05±0-86
10.81±0.42f
n QR 20.29+0.32
18.46+0.80*
n qft 19.50±0.31 ,q qi+n s?
u'yo 20.31+0.25 J-^-^J--u.3/
16.55±0.031t
18.07+2.97*
20.16±2.37*
_X 	 U-235 X ± Si
XRef (dPm/gram) (dpm/gram)
1.00 ""
1.05 :::
, n, 1.56±0.07 , ,1+n nR
1.45±0.06 J--3i-u.uo
0.63t0.05
n QQ
1.07±0.08*
°'97 O'.95±o!o2 0-93 + 0.02
0.96±0.03
0.96±0.20*
1.53±0.21*
X Recovery
XRef 7o
92
94
13
52
63
72
24
46
6
0.89 g^
0.91 76
7
9

^Rejected because  uranium tracer recovery was  less than 207o.

'Rejected by ASTM  test.

-------
     For this rejection criterion,  with n observations listed in
order of increasing magnitude by Xj <_ x2 < x3 < . . .  <_ x ,  if the
largest value xn is in question, then Tn Ts caTculated Ss  follows
              Tn = Cxn - x)/s                               (1)
where:
              T  = test criterion
               n

               x" = arithmetic average of all n values

               s = the estimate of the population standard
                   deviation based on the sample data


Alternately if xi rather than xn is the doubtful value, the
criterion is as follows:

              T! = (x - Xl)/s                               (2)


If the Tn or T1 value exceeds the critical value, the measure-
ment in question may be rejected.  Critical values of T for
various levels of significance are given in the ASTM reference
(ASTM 1977b) .   A 570 two-sided level of significance was employed
in deciding whether or not to reject a given measurement in the
present study.

     When a laboratory had made only one determination or when
one of the duplicates had been rejected, the one acceptable value
was used as the laboratory average.  The average value for each
laboratory was used to calculate the grand average value for the
collaborative study.  Uranium-235 concentrations reported by the
laboratories were divided by 0.844 because only 84.470 of the
total alpha branches from uranium-235 are included in a well-
resolved spectrum of natural uranium  (Sill, 1977).  The
laboratory calculations were checked to ensure that this
correction had not been made previously.

     In general, the procedure evaluated at Mound was  followed
by the participating laboratories, but a few minor deviations
were made.  Since Laboratory 5 did not have the necessary counting
equipment and since the alpha pulse height analysis system at
Laboratory 4 was being  repaired, the slides from these labora-
tories were counted at Mound and the resulting spectra were sent
back to these laboratories  to be analyzed as described in the
procedure.  Laboratory  1 used silver slides, rather than the
stainless steel  slides  recommended in  the procedure.   The only
laboratory that  deviated considerably  from  the procedure was
Laboratory 2.   This laboratory used an ammonium  oxalate procedure
for electrodeposition rather than  the  ammonium  sulfate procedure

                              13

-------
 given in the present method.   Three out of the eight deter-
 minations reported by Laboratory 2 had tracer recoveries  of  less
 than 207o and had to be rejected,  while the average uranium-232
 recovery for this laboratory  was only 377o.   Previous experience
 at  Mound has indicated that an ammonium sulfate procedure gen-
 erally gives better yields  than an ammonium oxalate procedure.
                      DISCUSSION  OF RESULTS

     A summary  of  the collaborative study results  is  given  in
 Table  9.   In  this  table,  the  grand averages  or  the average
 collaborative study  concentrations (Xc)  and  the standard
 deviations  (Sd)  of the individual  laboratory averages are
 presented  for the  uranium isotopes measured  for each  sample.
 These  statistics were calculated as follows  (Youden and Steiner
 1975):


                                                            (3)
             Sd =  (^1 -^c;  ]                              (4)


where:

             Xi =  average of duplicate results for
                  laboratory i for the given sample

             n =  number of laboratories providing
                  results for  the given sample


The precision standard deviation or the combined within-laboratory
standard deviation, Sr, and the standard deviation of the system-
atic errors  or the precision  of the method between laboratories,
85, are also given in Table 9.  The precision standard deviation
is estimated according to Youden's Formula (3)  (Youden and
Steiner, 1975) as follows for duplicate determinations:
            Sr = (Ed2/2n)                                   (5)

where:

             d = the absolute difference between the
                 duplicates


                              14

-------
    TABLE  9.   SUMMARY OF RESULTS FOR  URANIUM-IN-SOIL
                AND AIR COLLABORATIVE STUDY*

Tabulated Quantity
Sample
1
1
1
2
2
2
3
3
3
4
4
4
Isotope
U-238
U-234
U-236
U-238
U-234
U-235
U-238
U-234
U-235
U-238
U-234
U-235
Xc
0.19
0.25
1.31
1.87
2.68
0.090
21.6
37.9
1.70
20.95
20.66
1.01
Sd
0.09
(47%)
0.18
(72%)
0.08
(6.1%)
0.06
(3.2%)
0.21
(7.8%)
0.016
(18%)
1.7
(7.9%)
5.7
(15%)
0.40
(24%)
0.74
(3.5%)
0.65
(3.1%)
0.37
(37%)
S
0.05
(26%)
0.11
(44%)
0.15
(12%)
0.17
(8.9-1
0.28
(10%)
0.010
(11%)
1.9
(8.8%)
6.1
(16%)
0.28
(16%)
1.0
(4.8%)
0.92
(4.5%)
0.06
(6.0%)
sb
0 07
(33%)
0.16 •
(647.)
	
	
0.07
(2.6%)
0.014
(16%)
1.0
(4.6%)
3.7
(9.8%)
0.35
(21%)
0.22
(1.0%)
0.00
(0%)
0.37
(37?=)
Y +9 7
"Ref " bRef /0
0.21 ± 0.03
0.24 ± 0.04
1.32 ± 0.03
1.91 ± 0.06
2.77 ± 0.08
0.098 = 0.007
22.7 - 1.6
43.8 = 3.4
1.90 - 0.07
20.54 - 0.23
20.54 - 0.23
0.89 - 0.02
Difference
9.5
4.2
0.8
2.1
3.2
8.2
4.9
13
11
2.0
0.6
13

"'The  tabulated quantities  are defined as:   X  - collaborative study
 average  concentration,  S^ - standard deviation of  the laboratory
 averages, Sr - precision  standard deviation or combined within-
 laboratory averages,  S^ - standard deviation of  the systematic errors,
 ^Ref - SRef - reference concentration and standard deviation of the
 reference concentration.
                                15

-------
             n = the number of collaborating laboratories
                 reporting duplicates
The standard deviation of the systematic error, Su, is computed
from the other two standard deviations according to Youden's
Formula (4) (Youden and Steiner, 1975):
              2 =
   - S 2/2
      r
                                                           (6)
Also given in Table 9 are the reference concentrations and
estimated errors of these concentrations.  Reference values
for Samples 2 and 3 were obtained from the single-laboratory
evaluation.  The "% difference" given in Table 9 is the percent
difference between the reference value and the average reported
value.

     From the comparison of the average collaborative study
uranium concentrations with the reference values shown in Table
9, there appears to be good agreement of the data for all four
samples.  To determine whether the average collaborative study
concentrations agree with the reference values, the t-test was
used.  Two equations were used in applying the t-test.  The first
relationship applies to a situation in which the average of the
measured value and the average of the reference value each shows
a significant standard deviation; this equation is as follows
(Walpole and Myers,  1972):
            t =
where:
            X.
               c

            SRef
Xc - XRef
               t =
             Ref

               d
-d  + -Ref
       Ref
                                         n
(7)
test criterion

average of collaborative test results

average reference value

estimated standard deviation of
collaborative test results
              n  = number of collaborating laboratories
estimated standard deviation of
reference concentration
                              16

-------
            n^ f = number of determinations made in
                   obtaining the reference value


     The second relationship applies to a situation in which
the error in the reference value is considered to be negligible;
or, in other words, the reference value is considered to be the
true mean.   This equation is as follows (Youden and Steiner,
1975):
t = U:_^A
                                                           (8)
where:

            R = the reference value considered to be the
                true mean

            Other quantities are defined as in equation
            (7)


     The calculated values of t for the four reference samples
and the data used to calculate these values are given in Table
10.  Critical values of t  (tcj.j_t), determined for a 570 level of
significance,  are also given for comparison to the calculated t
values.  When t is less than tcrit, it can be said that the two
means agree.  It can be seen in Table 10 that all results from
the collaborative study agree with the reference values, except
the U-234 determination in Sample 3.  It should be pointed out
that three of the duplicate results reported by the laboratories
for Sample 3,  which are given in Table 7, show large variations
in duplicate values for this determination, and relatively poor
precision was obtained for the U-234 concentration of Sample 3
in the single-laboratory evaluation given in Table 3.  Since
only 40 mg of diluted pitchblende ore was added to the Micro-
sorban air filter, a homogeneity problem may be suspected;
however, the U-238 results show better precision than the U-234
results.  It would be expected that U-238 and U-234 activities
would be in equilibrium for Sample 3 but, instead, the U-234
activity is about a factor of two greater than the U-238 activity.
This is evidence that the  naturally occurring uranium series had
been altered in the preparation of this sample and may help
explain why the U-234 concentration appears to be less homogeneous
than the U-238 concentration.  Blank determinations of  the
polystyrene filters and plastic bags in which the samples were
sent to the participating  laboratories showed that the unexpected
U-234/U-238 ratio was not  caused  from  these materials.  Although
the reason  for the discrepancy between the reference value  and


                              17

-------
            TABLE 10.  t-TEST FOR  SYSTEMATIC ERRORS IN
                       COLLABORATIVE  STUDY RESULTS*
Tabulated Quantity3
Sample
1
1
1
2
2
2
3
3
3
4
4
4
Isotope
U-238
U-234
U-235
U-238
U-234
U-235
U-238
U-234
U-235
U-238
U-234
U-235
xc
0.19
0.25
1.31
1.87
2.68
0.090
21.6
37.9
1.70
20.95
20.66
1.01
+~ Sc
± 0.
± 0.
± 0.
± 0.
± 0.
± 0
± 1.
± 5.
± 0.
± 0
± 0
± 0.
09
18
08
06
21
.016
7
7
40
.74
.65
37
XRef
0.21
0.24
1.32
1.91
2.77
0.098
22.7
43.8
1.90
20.54
20.54
0.89
± SRef
± 0.
± 0.
± 0.
± 0.
± 0.
± 0
± 1.
± 3.
± 0.
± 0
± 0
± 0.
03
04
03
06
08
.007
3
4
07
.23
.23
02
nc nRef
5 4
6 4
6
7 12
8 12
6 12
8 9
8 8
6 8
5
5
4

0
0
0
1
1
1
1
2
1
1
0
0
t
.47
.13
.31
.40
.16
.17
.48
.51
.21
.24
.41
.65
crit
2.57
2.45
2.57
2.16
2.31
2.45
2.16
2.20
2.57
2.78
2.78
3.18
o ^^
 The  tabulated quantities are defined in  the text.
                                18

-------
collaborative study value is not apparent,  it is probably re-
lated to the reference sample,  rather than the analytical method
used in the preparation of the collaborative study.

     An additional objective of the present study was to determine
if the precision of the measured uranium concentrations approached
the precision expected from counting statistics.  The standard
deviations expected from counting statistics errors  were cal-
culated from the total counts and total counting time of each
duplicate determination which were supplied by the participating
laboratories.  They are given in Table 11, along with the standard
deviation of the uranium concentrations determined in each sample.
It can be seen that the errors calculated from the collaborative
study do not approach the error expected from counting statistics.
The average collaborative study error for determinations of
uranium activities above 1.0 pCi/g was found to be about 1070,
which is a factor of 3 higher than the error expected from count-
ing statistics.  Standard deviations for reference samples with
the highest uranium concentrations and lowest counting errors
were found to be about 370, and this might be considered the lower
limit for the precision of the present method.  The errors shown
in Table 11 for the determination of uranium in air  (Samples 1
and 3) were somewhat higher than the errors for the determination
of uranium in soil  (Samples 2 and 4), but this would be expected
since the counting errors for the air samples were also higher.

     Some comments about the collaborative  study were provided
by a few of the participating laboratories.  One laboratory
commented that the procedure was not long or time-consuming,
while another laboratory indicated that even though  the procedure
was good overall, they felt that it was very lengthy, especially
since only uranium  isotopes are separated and analyzed.   It was
pointed out by one of the participants that the uranium added to
the Microsorban air filters of  Sample 3 appeared to  differ from
one filter to its duplicate.  Two suggestions for possible changes
in the procedure were expressed.  These were to substitute an
ammonium iodide solution  (100 mg per 10 ml  6M HC1) for  the
hazardous hydriodic acid used in the anion  exchange  separation,
and to add the uranium tracer before ignition of the Microsorban
filters.

     The single-laboratory  and  multilaboratory  evaluations of  the
present procedure showed  that the method  provides a  relatively
simple, cost effective, and accurate means  of determining
uranium isotopes  in soil  and  air  samples  for uranium concentrations
of greater  than a few tenths  of a  disintegration per minute.
                               19

-------
TABLE 11.  OVERALL STANDARD DEVIATION OF COLLABORATIVE
           STUDY RESULTS AND STANDARD DEVIATIONS
           EXPECTED FROM COUNTING STATISTICS ERRORS"
Sample
Number
1
1
1
2
2
2
3
3
3
4
4
4
Isotope
U-238
U-234
U-235
U-238
U-234
U-235
U-238
U-234
U-235
U-238
U-234
U-235
Average Uranium
Concentration
(dpm/g or
dpm/ filter)
0.19
0.25
1.31
1.87
2.68
0.090
21.6
37.9
1.70
20.95
20.66
1.01
Std Dev
of Data
(dpm/g or
dpm/f ilter)
0.09
(47%)
0.18
(72%)
0.08
(6.1%)
0.06
(3.2%)
0.21
(7.8%)
0.016
(18%)
1.7
(7.9%)
5.7
(15%)
0.40
(24%)
0.74
(3.5%)
0.65
(3.1%)
0.37
(37%)
Std Dev Expected
From Counting Statistics
(dpm/g or dpm/ filter)
0.02
(11%)
0.03
(12%)
0.06
(4.6%)
0.04
(2.1%)
0.05
(1.9%)
0.005
(5.6%)
0.6
(2.8%)
0.9
(2.4%)
0.09
(5.3%)
0.38
(1.8%)
0.38
(1.8%)
0.04
(4.0%)
                          20

-------
                          REFERENCES

American Society for Testing and Materials, 1977 Annual Book
of Standards, Part 31, Designation:  D2907-75, P. 790,
Philadelphia, Pa., 1977a.

American Society for Testing and Materials, 1977 Annual Book
of ASTM Standards, Part 41, Designation:  E 178-75, p. 195,
Philadelphia, Pa., 1977b.

Bishop, C. T., A. A. Glosby, R. Brown, and C. A. Phillips,
"Anion Exchange Method for the Determination of Plutonium  in
Water:  Single-Laboratory Evaluation and Interlaboratory
Collaborative Study," U. S. Environmental Protection Agency
Report, EPA-600/7-78-122, Las Vegas, NV, 1978.

Bishop, C. T., V. R. Casella, and A. A. Glosby, "Radiometric
Method for the Determination of Uranium in Water:  Single-
Laboratory Evaluation and Interlaboratory Collaborative Study,"
U. S. Environmental Protection Agency Report, EPA  600/7-79-093,
Las Vegas, NV, 1979.

Danielsson, A., B. Ronnholm, and L. Kjellstron, "Fluorometric
Method for the Determination of Uranium in Natural Waters,"
Talanta, 20,  185  (1973).

Lee, H., T. 0. Peyton, R. V. Steele, and R. K. White,  "Potential
Radioactive Pollutants Resulting From Expanded Energy  Programs,"
U.S. Environmental Protection Agency Report,  EPA-600/7-77-082,
Las Vegas, NV, 1977.

Morrison, G.  H.,  and  H.  Freiser, Solvent Extraction  in Analytical
Chemistry, John Wiley and  Sons, Inc., New York, N. Y., p.  212,
I9TT

NCRP Report No. 45, Natural  Background  Radiation  in  the United
States, November,  1975.

Sill,  C. W    "Simultaneous  Determination of  238U,  234U, 230Th,
ZZbRa, and /luPb  in Uranium Ores,  Dusts, and  Mill Tailings,:
Health Physics,  33, 393  (1977).

U.  S.  Atomic  Energy Commission Regulatory  Guide  5.4,  Measurements
of  Radiohuclides  in the  Environment,  Sampling and Analysis of
Plutonium  in  Soil, May,  1974.
                               21

-------
Whittaker, E. L., and G. E. Grothaus, "Acid Dissolution Method
for the Analysis of Plutonium-239 and Plutonium-238 in Soil:
Evaluation of an Interlaboratory Collaborative Test and
Comparison with Results of a Fusion Method Test," U. S.
Environmental Protection Agency Report, EPA 600/7-79-081,
Las Vegas, NV, 1979.

Walpole, R. E., and R. H. Meyers, Probability and Statistics
for Engineers and Scientists, Macmillan Publishing Co.  Inc
New York,  N. Y., p. 197, 1972.

Youden, ¥. J., and E. H. Steiner, "Statistical Manual of the
Association of Official Analytical Chemists," Association of
Official Analytical Chemists, Washington, D. C.  1975.
                              22

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                          APPENDIX 1
           TENTATIVE METHOD FOR THE DETERMINATION OF
           URANIUM ISOTOPES IN SOIL AND AIR SAMPLES
     This appendix is a reprint of a procedure of the same title
by Vito R. Casella,  Carl T.  Bishop, Antonia A. Glosby,  and
Charles A. Phillips  of Mound Facility in Miamisburg,  Ohio.  The
report was prepared December 12, 1977,  for the U. S.  Environmental
Protection Agency under Contract No. EPA-78-D-X0143.   Mound
Facility is operated by Monsanto Research Corporation for the
U. S. Department of Energy under U. S.  Government Contract No.
EY-76-C-04-0053.  The procedure was prepared by Mound Facility
for distribution to participants in the interlaboratory
collaborative study and was designated as report number
MLM-MU-77-72-0001.
                               23

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                            PREFACE
     The analytical procedure described in this document is a
tentative method for the determination of uranium isotopes
in soil and air samples.  It is being collaboratively tested
according to an interagency agreement between the U. S.
Environmental Protection Agency (EPA) and the U. S. Department
of Energy (DOE).  Data from the collaborative test will be
examined and information on the precision and accuracy of the
method will be obtained.  A final report describing the results
of the collaborative study will be prepared.
                              24

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                              CONTENTS
SECTIONS                                                     PAGE

1.  Scope and Application

    1.1  General Considerations                               26
    1.2  Minimum Detectable Activity                          26
    1.3  Sensitivity                                          27
    1.4  Precision and Accuracy                               28

2.  Summary                                                   28

3.  Interferences                                             29

4.  Apparatus

    4.1  Instrumentation                                      29
    4.2  Laboratory Equipment                                 30
    4.3  Labware                                              32

5.  Standards, Acids,  Reagents

    5.1  Standards                                            33
    5.2  Acids                                                33
    5.3  Reagents                                             33

6.  Calibration and Standardization

    6.1  Standardization of the Uranium-232 Tracer Solution   34
    6.2  Determination of Alpha Spectrometer Efficiency       34

7.  Step by Step Procedure for Analysis

    7.1  Acid Dissolution                                     35
    7.2  Coprecipitation                                      36
    7.3  Ether Extraction                                     37
    7.4  Anion Exchange Separation                            37
    7.5  Electrodeposition                                    38
    7.6  Alpha Pulse Height Analysis                          39

8.  Calculation of Results

    8.1  Calculations of Uranium Concentrations               40
    8.2  Calculation of Alpha  Spectrometer Efficiency         40
    8.3  Calculation of Uranium Recovery  of  the  Chemical      ^
         Analysis

    References                                                42

                                25

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1.   SCOPE AND APPLICATION

    1.1   General  Considerations

         This procedure  applies to  the  determination  of  uranium
         isotopes in  soil or  air filter samples.   It  has been
         applied  to soils from  various  parts  of  the U.S.  and to
         both fiber glass and polystyrene  air filters.   Analysis
         of  soils for uranium at levels greater  than  0.01 dpm/g
         can be performed using this method for  10 gram  samples.
         Although 10  g samples  are  recommended,  it can be applied
         to  samples of up to  50g of soil.

         The method described in this procedure  can be carried out
         by  an experienced technician under the  supervision of a
         chemist  who  fully understands  the concepts involved in
         the analysis.   It involves relatively simple operations,
         but it should be utilized only after satisfactory results
         are obtained by  the  analyst when  replicate standard
         samples  are  analyzed.

    1.2   Minimum  Detectable Activity

         The minimum  detectable  concentration of a given  uranium
         isotope  is dependent upon the  size of the sample analyzed
         and the  minimum  detectable activity  (MDA) of the isotope.
         In  a given laboratory  situation this will also  depend upon
         the  observed  blank values (cf.  Section  3).  The  MDA is defined
         as  that  amount of activity which in  the same counting time,
         gives a  count which  is  different from the background count
         by  three times the standard deviation of  the background
         count.

         The  MDA  can be calculated from  some  typical parameters
         that might be expected  from the method described  in this
         procedure.  Suppose a sample is counted for 1000 minutes
         using a  silicon  surface barrier detector with a  25% counting
         efficiency,  the background in the energy  region of interest
         is  5 counts  in 1000 minutes,  and the chemical recovery of
         the  uranium tracer is 80%.   From the definition of the MDA,
                                 26

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     the sample count  would  have  to  be  seven  (ca.  3  x / 5)
     in 1000 minutes,  and to achieve this  count  under  the
     stated conditions would require 0.034 d/m of  activity.
     Thus,  a typical MDA for a  given uranium  isotope by this
     procedure would be 0.03 d/m.

1.3  Sensitivity

     Using the minimum detectable activity computed  in the
     last section and  considering a  10  gram soil sample, the
     lowest concentration of uranium-238,  as  mg  U-238/g of
     soil,  that could  be detected by this  method would be:

     0.034 d/m / (0.739 d/m/mg  x  lOg) = 0.0046 mg/g.

     The lowest concentration of  U-238  detectable  per  air  filter
     is the same as the MDA, i.e.  0.046 mg/filter.

     The sensitivity of this isotopic method  can be
     compared (Bishop,  1977) to methods which determine
     total uranium concentrations  fluorometrically.
     Although fluorometric methods are  comparable  in
     sensitivity to counting methods for U-238 (natural
     uranium),  fluorometric  methods  could  not detect
     other uranium isotopes  which are readily detect-
     able by counting  methods.  This is because  the
     isotopic method can be  used  to  detect much  smaller
     masses of these other uranium isotopes which  have
     high specific activities.  The  long lived isotopes
     of uranium along  with some of their properties
     of interest to this procedure are  given  in  Table
     1.
                  PROPERTIES OF URANIUM ISOTOPES
               OF INTEREST IN ENVIRONMENTAL SAMPLES
             Half-Life
     Isotope  (Years)
      U-232

      U-233

      U-234

      U-235


      U-236

      U-238
  72

1.62xlOv

2.47x10*

7. 1 xlO
8
2.39x10

4.51xl09
  Specific
  Activity
(dis/min/Mg)

4.75xl07

 21,000
 13,730

 4.76

 141

 0.739
Alpha Energies in MeV
	(Abundance)	

5.32 (68%), 5.27 (32%)

4.82 (83%), 4.78 (15%)

4.77 (72%), 4.72 (28%)

4.58 (8%), 4.40 (57%)
4.37 (18%)

4.49 (76%), 4.44 (24%)

4.20 (75%), 4.15 (25%)
                              27

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     ] . 4   Precision and Accuracy

           The precision of the method has not yet been evaluated,
           but based on experience with a similar procedure for
           uranium in water,  the precision is expected to approach
           that of counting statistics errors.  The accuracy is
           expected to be within the limits propagated from counting
           statistics and the uncertainty in the specific activity
           of the tracer used.
2.    SUMMARY
     The present procedure involves a nitric acid-hydrofluoric
     acid dissolution,  coprecipitation of uranium with iron hydro-
     xide,  an ether extraction if the sample contains iron as a
     major constituent,  separation of uranium by anion exchange,  and
     electrodeposition  of the uranium followed by alpha pulse height
     ana lysis.
     After adding uranium-232 tracer, organic matter is removed
     from the sample by  heating.   Subsequently,  the sample is
     decomposed by a nitric  acid-hydrofluoric acid digestion,
     and the uranium is  coprecipitated by making this solution
     basic with ammonium hydroxide (carbonate free).   The hydro-
     xide precipitate is dissolved in 8 M hydrochloric acid,
     which is extracted  with isopropyl ether to  remove the bulk
     of the iron present.   For samples with relatively low iron
     concentrations,  such as air  filters containing little
     particulate matter,  this extraction can be  omitted.

     The 8 M hydrochloric acid solution is passed through an  anion
     exchange resin column.   Uranium, polonium and bismuth will be
     adsorbed on the resin while  thorium and radium will  pass through
     the column.   Plutonium and any unextracted  iron are  also retained
     by the resin,  but  are eluted with 6 M HC1 containing hydrogen
     iodide.   The iodide ion reduces plutonium (IV) to plutonium  (III)
     and reduces the iron (III) to iron (II),  and neither of  these
     ions are retained  by the ion exchange resin in 6 M HC1.   The'
     uranium is eluted  from the column with 1.0  M HC1,  while  any
     zinc adsorbed on the column  will remain.   Electrodeposition  of
     the uranium onto a  stainless steel slide is performed,  and the
     slide is counted by alpha pulse height analysis using a  silicon
     surface barrier detector.
                                  28

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     When uranium-232 is used as a  tracer,  the  other  isotopes
     of uranium listed in Table 1 can  be  detected in  the alpha
     spectrum of an  unknown  sample.  From the alpha energies given
     in Table 1, it can be seen that  the alpha energy  of  uranium-232
     is at least 0.50 MeV higher than  the energy  of any  other
     uranium isotope.   Thus,  there  should be little interference
     from tailing of the uranium-232 into the lower energy alpha
     peaks.   If a sample contained  both uranium-233 and
     uranium-234, it would be very  difficult to resolve  these  two
     peaks since their principal alpha energies differ by only 0.05
     MeV.  The other uranium peaks  can be resolved if the resolution
     is good.

3.    INTERFERENCES

     3.1   The only  possible alpha  activity that  may  come through
           the chemistry of  the procedure is protactinium-231  (Ed-
           wards, 1968).  Protactinium-231 has  the following alpha
           energies  in MeV,  the abundance being given in parantheses:
           5.06 (10%), 5.02  (23%),  5.01  (24%),  4.95 (22%) and 4.73
           (11%). Thus, from Table 1, it can be seen that this
           protactinium-231  could possibly interfere  with the deter-
           mination  of uranium-233  or  uranium-234.

     3.2   In determining very low levels of uranium  isotopes in
           environmental samples, detector backgrounds and laboratory
           blanks must be accurately determined.   Blank  determinations
           must be made in order to ascertain that the contamination
           from reagents, glassware and  other laboratory apparatus  is
           negligible compared to the  sample that is  being analyzed.
           A blank determination should  be made in exactly the same
           way a sample determination  is  made.   For accurate analyses
           blank determinations should be consistent, and should be
           an order  of magnitude lower than activities obtained when
           analyzing samples.

4.    APPARATUS

     4.1   Instrumentation

           4.1.1  Alpha Pulse Height Analysis System - A system con-
                  sisting of a silicon surface barrier detector capable
                  of giving a resolution of 50 keV or better with
                  samples electrodeposited on flat mirror finished
                                  29

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             stainless steel slides is used.  The resolution
             here is defined as the width of the alpha peak in
             keV, when the counts on either side of the peak are
             equal to one-half of the counts at the maximum of
             the peak.  The counting efficiency of the system
             should be greater than 15% and the background in
             the energy region of each peak should be less than
             10 counts in 1000 minutes.

      4.1.2  Electrodeposition Apparatus - A direct current
             power supply, 0-12 volts and 0-2  amps,is required
             for the electrodeposition described in this procedure.
             A disposable electrodeposition cell is also recommended.
             An apparatus similar to that shown in Figure 1 has
             been used in the present procedure.  In the present
             procedure, the cell itself is surrounded by water,
             but the water is not circulated.   The electrodeposi-
             tion can be carried out without the water cooling.
             The cathode is a stainless steel slide with a
             polished mirror finish.  The diameter of the slide
             is 1.91 cm (3/4 in.) and the thickness is ca.  0.05 cm
             (0.02 in.).   The exposed cathode area during electro-
             deposition is 2 cm .

             The anode is a 1 mm diameter platinum wire with an
             8 mm diameter loop at the end above the cathode.

4.2   Laboratory Equipment

      4.2.1  Balance - top loading,  capacity 1200 g, precision
             ± 0.1 g.

      4.2.2  Balance - analytical, capacity 160 g,  precision
             + 0.1 mg

      4.2.3  Hot plate -  magnetic stirrer and stirrer bar.

      4.2.4  Centrifuge - capable of handling 100 ml or larger
             centrifuge bottles.
                             30

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                 Micro bell gloss
                 (Sorgent-Welch
                  Cot. No. S-4930)
Liquid scintillation counting
polyethylene vial, 25 ml capacity,
with bottom cut off containing
electrolyte solution
   Brass screw cap machined
   to fit 25 ril polyethylene
   vial, with 7/32" diameter by
   1/2" long  tube protruding
   from base of cap
  Platinum wire
  anode
     5/14" od glass
     tub* added to bell glass
                                                                                 Rubber tubing carrying
                                                                                 cooling water out
                                                                                                 Small rubber bulb
                                                                                        Stainless steel slide
                                                                                        3/4" in diameter
                     Stainless steel tubing,
                     3/8"odby 2 1/2" long,
                     electrical connection to cathode
                     mode here
Rubber stopper,
size 2
                                                                                    Rubber tubing carrying
                                                                                    cooling water in
                                     Figure 1.  Water Cooled Electrodeposition Apparatus
                                                     31

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4.3   Labware
      4.3.1  Graduated cylinders -  25 ml  to 100 ml.

      4.3.2  Beakers - glass,  100 ml  to 250 ml.

      4.3.3  Beakers - teflon,  250  ml with teflon covers.

      4.3.4  pH paper - pH range 2  to 10.

      4.3.5  Automatic pipettes - with disposable tips,
             volumes between 100 A and 1000A.

      4.3.6  Centrifuge bottles - 250 ml.

      4.3.7  Ion exchange  columns - approximately 1.3  cm  ID,
             15 cm long with 100 ml reservoir.

      4.3.8  Pipettes - glass,  Class  A.

      4.3.9  Disposable pipettes -  2  ml glass eye-dropper
             type,  with rubber  bulb.

      4.3.10  Dropping bottles.

      4.3.11  Watch glasses.

      4.3.12  Polyethylene  washing bottles.

      4.3.13  Glass stirring  rods

      4.3.14  Safety glasses  or  goggles.

      4.3.15  Rubber gloves.

      4.3.16  Crucible tongs  - platinum  tipped.

      4.3.17  Beaker tongs.

      4.3.18  Spatulas.

      4.3.19  Heat  lamp-mounted  on ring stand for  drying slides.
                             32

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5.   STANDARDS,  ACID,  REAGENTS

    5.1  Standards

         5.1.1    Standardized uranium-232 solution.

    5.2  Acids

         Reagent grade,  meeting American Chemical Society (ACS)
         specifications;  diluted solutions prepared with distilled
         deionized water.

         5.2.1    Nitric  acid - concentrated (16 M).

         5.2.2    Hydrochloric acid - concentrated (12 M, 8 M,  6  M,
                 1.0 M,  0.5 M.

         5.2.3    Sulfuric acid - concentrated (18 M), 1.8 M.

         5.2.4    Hydrofluoric acid - concentrated (48% solution).

         5.2.5    Hydriodic  acid - concentrated (48% solution).

    5.3  Reagents

         Reagent grade,  meeting ACS specifications; solutions
         prepared with distilled deionized water.

         5.3.1    Ferric  chloride - in 0.5 M HC1 containing 10 mg
                 of iron per ml of solution.

         5.3.2    Ammonium hydroxide - concentrated (15 M), 1.5 M,
                 0.15 M.

         5.3.3   Anion exchange resin - Bio Rad AG1-X4  (100-200
                 mesh) chloride form.  (Available from Bio Rad.
                 Laboratories, 3rd and Griffin Avenues, Richmond,
                 California, 94804).  A column is prepared by
                 slurrying this resin with 8 M HC1 and pouring it
                 onto a column of inside diameter approximately
                                  33

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                 1.3 cm.  The height of the column of resin should
                 be about 10 cm.

         5.3.4   Sodium hydrogen sulfate solution ca. 5% in 1 M
                 H SO ;  dissolve 10 g of the NaHSO •H 0 in 100 ml
                 or water and then carefully add 100 ml of 2 M H SO .
                                                                4-i  Tt
         5.3.5   Preadjusted electrolyte - 1 M ammonium sulfate
                 adjusted to pH 3.5 with 15 M NH, OH and 18 M H SO
                                                H-             £  Q •
         5.3.6   Thymol  blue indicator, sodium salt (available
                 from Fisher Scientific Company) - 0.04% solution.

         5.3.7   Ethyl alcohol - made slightly basic with a few drops
                 of 15 M NH OH per 100 ml of alcohol.

6.  CALIBRATION AND STANDARDIZATION

    6.1  Standardization of the Uranium-232 Tracer Solution

         If a standard uranium-232 solution is not available, a
         freshly purified sample of uranium-232 could be standard-
         ized by mixing  a known amount of another standard solution
         such as uranium-236,  with a known amount of the solution to
         be standardized,  mixing thoroughly and electroplating the
         mixture.   From  an alpha pulse height analysis of the mixture
         the specific activity of the uranium-232 solution could be
         determined.   Alternately,  a freshly purified solution of
         uranium-232  could be  standardized by 2-rr counting. Weighed
         aliquots of  the solution free of hydrochloric acid could be
         evaporated on platinum or stainless steel slides and counted
         with a 2-n proportional counter.   The efficiency of the 2-n
         proportional counter  can be accurately determined with a
         National Bureau of Standards alpha-particle  standard.   When
         using these  standards,  corrections for resolving time and
         backscattering  must be made if necessary.

    6.2  Determination of  Alpha Spectrometer Efficiency

         Determination of  the  alpha spectrometer counting efficiency
         is not necessary  to get an accurate concentration of the
         uranium isotopes  in the sample being analyzed,  since the
         counting efficiency of the electroplated sample is the same
         for the tracer  uranium isotope and for the unknown uranium
         isotope.   This  efficiency  cancels out when the concentration
         of the unknown  uranium isotope is calculated (cf.  Section 8.1)
                                  34

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          A determination of  the alpha spectrometer  counting
          efficiency is  required to  calculate the  uranium
          recovery of a  particular analysis.   To determine
          this  efficiency requires that one count  an alpha
          particle source of  known alpha particle  emission rate
          under the same conditions  that the samples are
          counted.  The  alpha particle counting efficiency is
          then  calculated as  illustrated in Section  8.2.

7.   STEP BY STEP PROCEDURE FOR ANALYSIS

    7.1  Acid Dissolution

         7.1.1   Weigh a  representative  10.0 ± 0.1 grams of 100
                mesh soil sample or  the glass fiber  filter(s)
                and transfer  to a casserole.  If a Microsorban
                (polystrene)  filter(s) was used,  place the
                filter(s) into a 150-ml or 250-ml  Pyrex beaker
                and cover with a watch glass.

         7.1.2  Add an appropriate quantity of uranium-232 tracer.
                If the activity "is expected to be less than 1 dpm/g,
                or is unknown, add 10 dpm of tracer.  For higher
                levels add as much uranium-232 tracer as the esti-
                mated activity of uranium in the sample.  If a
                Microsorban filter(s) was used, add the uranium-232
                tracer after Step 7.1.3.

         7.1.3  Heat the casserole containing the soil sample or
                glass fiber filter(s) at 600°C for four hours in
                a muffle furnace; remove, and cool.   If a Microsorban
                filter(s) was used,  place the Pyrex beaker in a
                muffle furnace at 200°C for 1 hour.   Increase the
                temperature at 1 hr intervals to 300°C, 400°C and
                550°C.  Muffle for 2 or 3 hrs at 550°C or until only
                a brown powdery ash remains .  Remove and cool.

         7.1.4  Transfer the  sample to  a 250-ml Teflon beaker,
                rinsing  the casserole with  10 ml portions of
                16 M HNO- to  a final volume of 60 ml of nitric
                acid.  For Microsorban  filter(s) rinse  the
                beaker with 5 ml  portions of  16 M HNC>3  to a
                final volume  of 30 ml  of nitric acid.
                                   35

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     7.1.5   Carefully add 30 ml of 48% hydrofluoric acid
             (20 ml for Microsorban filters), cover with a
             teflon watchglass and heat on a hotplate with
             frequent stirring for about 1 hr.  Remove from
             the hotplate and cool.  (CAUTION:  HF is very
             hazardous.  Wear rubber gloves, safety glasses
             or goggles, and a laboratory coat.  Avoid breathing
             HF fumes.  Clean up all spills and wash thoroughly
             after using HF).

     7.1.6   Carefully add 30 ml (20 ml for Microsorban filters)
             each of 16 M HNO  and HF (48%) and digest with some
             stirring for an additional hour.

     7.1.7   Remove from the hotplate and cool to room tempera-
             ture.   Slowly add 20 rnl of 12 M HC1 and heat on a
             hotplate with some stirring until the solution has
             evaporated to a liquid volume of approximately 10 ml.

     7.1.8   Add 50 ml of distilled water and digest on a hot
             plate with stirring for 10 minutes to dissolve the
             soluble salts.

     7.1.9   Cool and transfer the total sample into a 250-ml
             centrifuge bottle with a minimum of distilled water
             from a wash bottle.   If any insoluble residue is
             present,  the sample should be centrifuged and the
             supernate should be transferred into another centrifuge
             bottle.   This residue should be washed with 10 ml of
             1.0 M HC1 which is added to the supernate.   Discard
             the insoluble residue.  Proceed to section 7.2,
             Coprecipitation.

7.2  Coprecipitation

     7.2.1   Add 20 rag of iron as Fed   in 0.5 M HC1 to the
             centrifuge bottle and stir.   (This step is usually
             not necessary for soil samples containing iron).
                               o_
     7.2.2   Add 15 M  NH OH  (CO   free) while stirring to preci-
             pitate the iron.   Continue adding 15 M NH OH to raise
             the pH to 9-10  as determined by pH paper,  then add
             5  ml  in  excess.
                             36

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     7.2.3   Centrifuge for approximately 5 minutes, decant
             and discard the supernate.

     7.2.4   Dissolve the precipitate with a minimum of 12 M
             HC1 and add 8 M HC1 to a volume of about 50 ml.
             Transfer the solution to a 250-ml separatory funnel
             using  two 5-ml rinses of 8 M HC1 and proceed to
             Section 7.3, Ether Extraction.
7.3  Ether Extraction

     7.3.1   Add 60  ml of  isopropyl  ether  to  the  separatory
             funnel  and  shake  the  solution for  two minutes.
             Allow  the phases  to separate  and then  transfer
             the aqueous phase (lower  phase)  to a second
             separatory  funnel.  Add 5-ml  of  12 M HCl  to the
             aqueous phase.

      7.3.2  Repeat this  ether extraction two more  times.   The
             bulk  of the  iron is  removed  as  evidenced by  the
             appearance of  a  yellow color in the organic  phase.
             (If the sample has a very high  concentration of  iron,
             additional extractions may be necessary.)

      7.3.3   Transfer  the aqueous phase to a 150-ml beaker,
              boil  for  15  tnin, and proceed with Section 7.4,
              Anion Exchange Separation.

 7.4  Anion Exchange Separation

      7.4.1   Condition  the anion  exchange resin  column  (prepared
              as described in  Section 5.3) by rinsing  the column
              with  4 column volumes  of 8 M HCl.

      7.4.2   Transfer  the sample  from Step 7.3.3 to the condi-
              tioned anion exchange  resin.

      7.4.3   After the sample has passed through the column,  elute
              any unextracted iron (and plutonium if present)  with
              6 column volumes of  6  M HCl containing 1 ml of concen-
              trated HI per 50 ml  of 6 M HCl (freshly prepared).
                               37

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     7.4.4   Rinse the column with an additional two column
             volumes of 6 M HC1.

     7.4.5   Elute the uranium with six column volumes of 1.0 M
             HC1.

     7.4.6   Evaporate the sample to about 20 ml and add 5 ml of
             16 M HNO
                     O
     7.4.7   Evaporate the sample to near dr^ness.

7.5  Electrodeposition

     7.5.1   Add 2 ml of a 5% solution of NaHSCKH 0 in 1 M
             H SO  to the sample.
              <£  T
     7.5.2   Add 5 ml of 16 M HNO   mix well and evaporate to
             dryness, but do not  Bake.

     7.5.3   Dissolve the sample  in 5 ml of the preadjusted elec-
             trolyte (cf. Section 5.3), warming to hasten the
             dissolution.

     7.5.4   Transfer the solution to the electrodeposition
             cell  using  an additional 5-10 ml of the electrolyte
             in small increments  to rinse the sample container.

     7.5.5   Add three or four drops of thymol blue indicator
             solution.   If the color is not salmon pink, add
             1.8 M HnSO  (or 15 M NH^OH) until this color is
                —  2t  4       —   4
             obtainea.

     7.5.6   Place the platinum anode into the solution so that
             it is about 1 cm above the stainless steel slide
             which serves as the  cathode.

     7.5.7   Connect the electrodes to the source of current,
             turn  the power on, and adjust the power supply to
             give  a current of 1.2 amps.  (Constant current power
             supplies will require no further adjustments during
             the electrodeposition.)

     7.5.8   Continue the electrodeposition for a total of
             1 hr.
                             38

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     7.5.9   When  the electrodeposition  is to be terminated,
            add 1 ml of  15 M NH.OH and  continue the electro-
                           —   4
            deposition  for 1 min.

     7.5.10  Remove  the  anode from the cell  and then turn off  the
            power.

     7.5.11  Discard the solution  in  the cell and  rinse  the
            cell  2  or 3 times  with 0.15 M NH4OH.

     7.5.12  Disassemble the cell  and wash the  slide with
            ethyl alcohol  that has been made basic with NH^OH.

     7.5.13  Touch the edge of  the slide to  a tissue to  absorb
            the alcohol from the  slide.

     7.5.14  Dry the slide, place  it  in  a box,  and label for
            counting.   (The sample should be counted  within a
            week, since uranium-232  daughters  grow  into the
            sample  and  possibly  interfere with the  determination
            of certain  other uranium activities.)

7.6  Alpha Pulse Height  Analysis

     7.6.1  Count the  samples  for at least  1000 minutes or
             longer  if  the  detector efficiency  is  less than
             15%,  if the tracer recovery is  low,  or  if the
            unknown uranium activity is low.

     7.6.2  Check the  alpha pulse height analysis spectrum for
            peaks at the uranium-233,  uranium-234,  uranium-235,
             uranium-236 and/or uranium-238  alpha energies  (see
            Table 1) and determine  the  total  counts in each peak.
             Where two isotopes are  close in energy,  complete
             resolution  may not be possible.  (This  is the  case
             with  uranium-236  and uranium-235,  for example.)

     7.6.3   Make  the necessary background  corrections.   (The
             background should  be determined by a 4000 minute
             or longer count.)
                             39

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          7.6.4    Make a blank correction for each peak, if
                   necessary.

8.    CALCULATION OF RESULTS

     8.1  Calculations of Uranium Concentrations

          By integrating the appropriate energy peak along with the
          uranium-232 tracer peak,  the concentrations of the corres-
          ponding uranium isotope can be determined (cf. Table 1).
          This concentration is calculated as follows:

                X.  = C.  x A
                 i    __i	t                     ,R  .
                     C  x W                      (8'1)
                      t    s

          where X.   =  the concentration of the unknown uranium
                       isotope in d/m/g of soil or d/m/ filter.

                C.   =  the net sample counts in the energy region
                       corresponding to the uranium isotope being
                       measured.

                A   =  the activity of the uranium-232  tracer added
                       to the  sample in d/m.

                C   =  the net sample counts in the uranium-232 tracer
                       energy  region of the alpha spectrum.

                W   =  the weight in grams of the soil  sample taken
                       for analysis; W  is omitted from this formula
                                      o
                       (W =1)  when  the sample is an air filter.
                         S

     8.2  Calculation of Alpha Spectrometer Efficiency

          The absolute counting efficiency of the alpha spectrometer,
          e,  must be determined in  order to calculate the uranium
          recovery  of the an-alytical procedure.

          To  determine this efficiency requires a standard source
          of  a known alpha particle emission rate:
                                  40

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        E   = Rs/Ra                      (8.2)

     where R  = the net  counting rate of the  standard  source
                in the energy region  of  the alpha  emitter  of
                interest in counts  per minute.

           R  = the absolute alpha  particle emission rate  of
                the alpha emitter of  interest  in alpha dis-
                integrations per minute.

8. 3  Calculation of Uranium Recovery  of  the Chemical Analysis

     The uranium recovery efficiency  E (%) expressed  in percent
     is given by:

          = Ct x 100%                            (g 3)
            t x A  xe

     where t=the counting time in minutes and the other terms
     are as defined in Sections 8.1 and 8.2.
                              41

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                          REFERENCES
F. Baltakmens, "Simple Method for the Determination of
Uranium in Soils by Two Stage Ion Exchange," Anal. Chem.,
47, 1147 (1975).

C. T. Bishop, V. R. Casella, R. Brown, A. A. Glosby,
C. A. Phillips and B. Robinson, "Tentative Method or
the Determination of Uranium Isotopes in Water (By a
Coprecipitation Anion Exchange Technique)." Unpublished
report MLM-MU-77-61-0001, Mound Laboratory, 1977.

K. W. Edwards, "Isotopic Analysis of Uranium in Natural Waters
by Alpha Spectrometry," Radiochemical Analysis of Water,
Geological Survey Water Supply Paper 1696-F, U. S. Government
Printing Office, Washington, D. C.,  1968.

  ?. H. Essington and H. P. Patterson, "Determination of
 38u, 233-234(j in Soil and Vegetation Samples  (Tentative),"
Nevada Applied Ecology Group Procedures Handbook for Environ-
mental Transuranics, NVO-166, Vol. 1, p. 205, October 1976.

J. E. Gindler, "The Radiochemistry of Uranium," NAS-NS-3050,
National Academy of Sciences - National Research Council,   1962

J. Korkisch, "Modern Methods for the Separation of Rarer Metal
Ions," Pergamon Press, New York, 1969, P. 62.

K. A. Kraus and F. Nelson, "Anion Exchange Studies of the
Fission Products," Proceedings of the International
Conference on the Peaceful Uses of Atomic Energy," Geneva,
1955, 7, 113, Session 9B1, p. 837, United Nations (1956).

N. A. Talvitie, "Electrodeposition of Actinides for Alpha
Spectrometric Determination," Anal.  Chem. 44, 280 (1972).

U. S. Atomic Energy Commission, "Measurement of Radionuclides
in the Environment - Sampling and Analysis of Plutonium in
Soil," U. S. Atomic Energy Commission Regulatory Guide 4.5,
May, 1974.
                             42

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                         APPENDIX 2
            COLLABORATIVE STUDY INSTRUCTIONS


                  URANIUM IN  SOIL AND AIR


                        (January 1978)


 1.  Use the procedure "Tentative Method for  the  Determination
    of Uranium Isotopes in Soil and Air Samples" by V. R. Casella
    et. al., December 2, 1977.

 2.  If you have not analyzed samples using a procedure similar to
    the one to be used in the collaborative  study,  a  few known
    samples should be analyzed before analyzing  the collaborative
    study samples.

 3.  Special reagents that you might not have on  hand,  such  as  the
    ion exchange resin, will be furnished by Mound  if you desire.
    Contacts are given below.

 4.  Additional amounts of any sample are available  if required.
    Contacts are given below.

 5.  All samples should be analyzed in duplicate.  For sample
    78-4, analyze five grain aliquots rather  than ten  grams.

 6.  Uranium concentrations may bo as low as  0.5  dis/min/g  or
    0.5 dis/min/filter.  Laboratory blanks should be  determined
    in your laboratory  to be certain that they are  not a problem
    at these uranium concentrations.

 7.  Use the uranium-232 tracer, U-10, for this study.  Data on this
    tracer  is attached  to these instructions.  Using  500X  of this
    tracer  gives  10.4 dis/min of U-232.

 8.  When  analyzing  the Microsorban samples,  do not  remove  the
    filter  from the plastic bag in which it is contained;  ignite the
    filter  and bag  together when beginning the analysis.

 9.  The water cooled electrodeposition apparatus shown in  Figure 1
    of  the  procedure is only an illustration.  Water  cooling is  not
    required, and any apparatus producing a suitable  slide  foi
    alpha pulse height  analysis is satisfactory.

10.  Samples should  be  counted  for  1000 minutes or at least long;
    enough  to accumulate  200 counts  In an unknown alpha peak.

11.  Report  your results on  the data  sheet attached.  Individual
     counting  data is requested so  that  the  counting staizistice
     error can be  resolved  from other experimental errors.
                                43

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                            APPENDIX 3
                    DATA ON URANIUM-232 TRACER
Isotope:  U-232                              I.D.  No.:   U-10

Date Prepared:   11/28/77

Specific Activity:   20.2 dis/min/gram (±2%)(on date  prepared)

Density:  1.031 g/cm3 at 20°C

Acid Medium:   1 M HN03

Source:  U.S.  ERDA - Health and Safety Laboratory, purified by
                     ion exchange and standardized at Mound Facility.

Half Life:  72 years

Approximate Volume in Glass Ampoule:   6 ml

Opening Instructions:  The constriction of  the glass ampoule has
                       been previously scored and  reinforced vrith
                       a blue ceramic band.   It can  readily be
                       broken without a file.  The small polyethylene
                       bottle with the long narrow neck,  enclosed
                       with the  ampoule, may be used to remove  the
                       tracer from the opened ampoule and for weighing
                       the amount of  tracer added  to each sample.

Prepared At:   Mound Facility
              Monsanto Research Corporation
              Miamisburg,  Ohio  45342
                                 44

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                         APPENDIX 4
             LABORATORIES PARTICIPATING IN  THE
        URANIUM IN SOIL AND AIR  COLLABORATIVE STUDY
Allied Chemical Corporation
Idaho Falls,  Idaho

Argonne National Laboratory
Argonne, Illinois

Arkansas Department of Health
Little Rock,  Arkansas

Eberline Albuquerque Laboratory
Albuqueque, New Mexico

LFE Environmental Analysis  Laboratories
Richmond, California

Ohio State University
Columbus, Ohio

Reynolds Electrical and Engineering Co.,  Inc.
Las Vegas, Nevada

U. S. Energy Research and Development Administration
Environmental Measurements  Laboratory
New York, New York
                              45

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
1. REPORT NO.
                             2.
                                                           3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
 RADIOMETRIC METHOD  FOR THE DETERMINATION OF URANIUM  IN
 SOIL AND AIR:  Single  Laboratory Evaluation and
 Inter!aboratory  Collaborative Study
             5. REPORT DATE
                February  1980
             6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)

 V. R. Casella, C.  T.  Bishop, and A. A. Glosby
                                                           8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
 Monsanto Research  Corporation
 Mound Facility
 P.O. Box 32
 Miamisburg, Ohio   45342
             10. PROGRAM ELEMENT NO.

                  INE833
             11. CONTRACT/GRANT NO.
              IAG-EPA-78-D-X0143
12. SPONSORING AGENCY NAME AND ADDRESS
 U. S. Environmental  Protection Agency—Las Vegas,  NV
 Office of Research  and  Development
 Environmental Monitoring  and Support Laboratory
 Las Vegas, Nevada   89114
             13. TYPE OF REPORT AND PERIOD COVERED

                 4/1/77 ~ 10/1/78	
             14. SPONSORING AGENCY CODE
                 EPA/600/07
15. SUPPLEMENTARY NOTES
 Mound Facility  is  operated by Monsanto Research Corporation for the U.S. Department
 of Energy under Contract  No.  DE-AC-04-76-DP00053
16. ABSTRACT
 Results of a single-laboratory evaluation and an interlaboratory collaborative study
 of a method for determining uranium isotopes in soil  and  air samples are presented.
 The method is applicable to 10-gram soil samples and  to both glass fiber and poly-
 styrene (Microsorban)  air filter samples.  Sample decomposition is accomplished with  a
 nitric-hydrofluoric  actd dissolution.  After a solvent extraction step to remove most
 of the iron present,  the uranium is isolated by anion exchange chromatography and
 electrodeposition.   Alpha spectrometry is used to measure the uranium isotopes.

 Two soil samples, a  glass fiber air filter sample, and a  polystyrene air filter sample
 were used to evaluate  the method for uranium concentrations  ranging from a few tenths
 to about one hundred  disintegrations per minute per sample.   Tracer recoveries for the
 single-laboratory evaluation averaged 78 percent, while the  tracer recoveries for the
 collaborative study  averaged 66 percent.  Although the precision of the collaborative
 study results did not  approach counting statistics errors, the measured uranium
 concentrations for these samples agreed to within 5 percent  of the reference concen-
 trations when the uranium concentration was greater than  one disintegration per minute
 per gram of soil or  one  disintegration per minute per air filter.
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
   Uranium
   Quantitative analysis
   Quality assurance
   Soil and air
                            68F
                            77B
                            99B, E
18. DISTRIBUTION STATEMENT
   RELEASE TO PUBLIC
                                              19. SECURITY CLASS (ThisReport)
                                                 UNCLASSIFIED
                           21. NO. OF PAGES
                              14
20. SECURITY CLASS (Thispage)

   UNCLASSIFIED
                           22. PRICE
EPA Form 2220-J (Rev. 4-77)   PREVIOUS EDITION is OBSOLETE

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