-------
Collection
Data
Form
1.
2.
3.
4.
5.
Assign, sample laboratory
number
Transcribe collection info on-
to 4-part log-in form
Complete missing items,
correct errors
Distribute 4-part form
Prepare and submit sample
for analysis
Sample
Analysis
4-part
log-in form
_y
White copy
to keypunch
room for
header
Yellow copy
accompanies
sample for
Y analysis
Blue copy
to project
director
Chem, card
accompanies
sample for
chemistry
FIGURE 6
SAMPLE CONTROL PROCESS
12
-------
III. GAMMA ANALYSIS SYSTEM
A. General Description
The "gamma system" encompasses the sample handling, counting, data
analysis and interpretation, and reporting procedures involved in
quantitative gamma spectral analysis. In processing large numbers
of samples by quantitative gamma spectral analysis, a number of
assumptions must be made prior to the analysis. The most important
are related to detector response characteristics, system reproduci-
bility and radioactivity standards library. An analysis is iriade and
the results reviewed in order to validate the initial assumptions.
If the assumptions are found to be incorrect, they must be altered
and the analysis repeated. This process is shown schematically in
Figure 7.
B. Instrumentation
The gamma counting facility consists of five analyzers each operating
in split mode with two thalium activated sodium iodide detectors. The
analyzers are TMC Model 404C, 400 channels, with multiple input. The detec-
tors are 4-inch-thick by 4-inch-diameter crystals and are manufactured by
the Harshaw Chemical Corp. The crystal housing, hermetically sealed,
is of 0.019-inch Type 304 stainless steel.. A 3. 1/2-inch-diameter by
5/16-inch-thick Vycor optical window is coupled to a 5-inch-diameter
RCA Venetian blind dynode multiplier phototube, Type 20fc5.
The detector assembly is seated on a lucite shelf in a
13
-------
steel shield of 6-inch-thick walls. The chamber within the shield is
20 by 20 by 24 inches, lined with 0.1-inch lead, 0.03-inch cadmium and
0.015-inch electrolyte copper.
Readout from each analyzer is by means of perforated tape and type-
writer (the perforated tape is processed by the computer for analysis
and data storage).
The gamma spectrometer counting arrangement is shown in Figure 8.
C. Calibration and Quality Control
Routine samples are counted in one of four standard geometries.
Four special purpose geometries are used for limited studies where
sample quantity or processing may require a non-standard configuration.
TYPE GEOMETRY DESCRIPTION
Standard 01 2-inch-diameter planchet
Standard 02 4-inch-diameter planchet
Standard 03 400-ml polyethylene container
Standard 06 3.5-liter Marinelli beaker
Special 12 250-ml polyethylene container
Special 15 1-liter cubitainer
Special 16 250-ml resin
Special 17 Soil
A radioactive isotope standard is counted on each detector in each
geometry for each nuclide to be analyzed. Table 2 summarizes the
14
-------
standards library as of January 1, 1970. An effort is made to recalibrate
the more common long-lived isotopes on a yearly basis. For nuclides
for which standards are not available, a gamma efficiency vs. energy
curve is used for quantisation (Figure 9).
A 400-minute background count is accumulated daily on each system.
Both the standard spectra and background count are processed through
appropriate computer programs and stored on disk for recall during
data analysis.
In quantitative and/or qualitative analysis by gamma spectroscopy,
the validity of the analysis depends on the satisfactory and
reproducible operation of the instrumentation. The first level of
quality control, then, is that applied to the instrument itself.
1. System Response
System response is checked daily by counting a 207Bi
reference standard. This isotope has a 30-year half-life
and two prominent gamma emissions at 0.570 MeV and 1.063 MeV
(Figure 10). The source is counted for ten minutes and read out
on punch paper tape. The tape is then run through a computer
program (BI207)* and the following parameters calculated:
*
Names in capital letters designate the name of the computer code in
the process. Full documentation of all computer programs used by the
SWRHL is available at the Laboratory. Documentation includes a com-
plete index of programs, one-page summaries identifying the nature of
the programs, source language listings, flow charts, data set-up
information and operating instructions.
15
-------
1) peak locations
2) difference between peak locations
3) sum of counts under photopeak
4) resolution
5) peak ratio
A sample computer printout is shown in Table 3. Peak
location and interval are maintained within 0.5 channels
of the theoretical. If both peaks are shifted equally,
a zero shift is indicated. A gain change is indicated
by a proportional shift. Daily corrections are made to
maintain the energy calibration within the specified limits.
Control charts are updated daily to evaluate long-term
trends. These are maintained for each detector system.
The sum of counts within the photopeak provides a check on
counting efficiency. Resolution provides a measure of
energy separation. Charting of sum counts can detect long-
term failure of the detector while resolution charting can
indicate gross detector failure.
Peak ratio is the ratio of counts in the two peaks. Although
not necessary as a quality control check, it does provide
another sensitive indicator of change in detector response.
2. Background
Background data are accumulated daily to check abnormalities
16
-------
that may occur on a long-term basis. After normal opera-
tions, the systems are set for a 400-minute background
count. The gross gamma count is reported daily and plotted
on a control chart. If the background is unusually high,
the spectrum is checked to determine the reason for the
increase. A background quality control chart is maintained
for each system to detect long-term trends and fluctuations.
D. Sample Counting and Data Flow
Figure 11 shows the routine sample and data flow through the gamma
system. The,sample is received along with the yellow copy of the
log-in sheet. Collection information is transcribed to a gamma
analysis coding record (Figure 12). Counting data are added to
both gamma code record and log-in form. The sample is counted from
10 to 40 minutes depending on sample type and sample load.
Count Time (Minutes)
Sample Type
Air Filter
Charcoal Cartridge
Milk
Water
Feed
Vegetation
Routine
10
10
40
40
40
10
Event-Related
10
10
20-40
20-40
20-40
4-10
17
-------
Count data are read out on punched paper tape and typewriter
printout. The gamma analysis coding record is used to identify
the sequence of spectra on the punched paper tape. The yellow
log-in form is attached to the typewriter printout to identify
spectra. This becomes the hard copy of the raw data that is
retained for future reference as needed.
The gamma coding record is keypunched, producing a gamma header
card for each sample counted. The punched tape is converted to
cards and merged with the appropriate header card (PONO). The data
are then processed through a gamma analysis program (GMTRX) which
utilizes the simultaneous equation technique to resolve the spectrum.
Radionuclide standards and background information are stored on disk
. for access by the gamma analysis computer program. Figure 13 is a
\
listing of typical calculation results. These data are reviewed
and the results posted on the hard copy. A plot of the spectrum can
be generated if necessary. The results are then keypunched onto
cards for subsequent reporting.
.E. Data Analysis
The principles involved in quantitative gamma spectral analysis
. by the simultaneous equation or matrix technique are described in
the Public Health Service Training Manual, "Radionuclide Analysis
by Gamma Spectroscopy." A copy of this discussion is included in
Appendix B.
18
-------
Data relating to the interference coefficients among radionuclides
are utilized in the matrix technique of gamma spectral analysis.
Three files of data are maintained for routine analysis, each
containing a library of eight radionuclides. These are grouped,
according to whether the predominant activity is of long, inter-
mediate or short half-life as follows:
Long-Lived
Isotope Peak
0.13
0.36
0.51
0.67
0.76
0.84
1.46
1.60
Intermediate
Half-Life
Short Half-Life
I'+'tCe
131i
106Ru
137Cs
95Zr
Isotope
i"Nd
i«Ce
132Te
i«3Ce
131!
103RU
95Zr
140Ba
Peak
0.09
0.14
0.23
0.29
0.36
0.50
0.76
1.60
Isotope
"ice
131!
133!
137QS
132Te
"Mo
135!
40K
Peak
0.14
0.36
0.53
0.67
0.23
0.75
1.28
1.46
1.
2.
3.
4.
5.
6.
7.
8.
The appropriate data set is utilized according to the circumstances,
Knowledge of event characteristics allows special data sets to be
specified. These data can be assembled in any combination up to
eight radionuclides.
The program calculates the activity concentration of each of the
nuclides at the time of count and at time of collection. If an
isotope is determined absent, it is deleted from the matrix and a
19
-------
recalculation is executed. This process continues until the matrix
is exhausted.
Other programs utilized in support of GMTRX are:
PQNO: Reads gamma spectra from paper tape output and converts to
cards. Checks for valid characters and format. An option to sum
200 channels and compare to specified limits is included.
BKGD: Reads background spectra from cards and writes information
calculated from spectra onto disk for use by GMTXD. Reads the
peak regions of nuclides from the standard information on the disk
and calculates the background cpm for each photopeak. These values
are then written on the disk along with the standard information
needed for GMTXD.
DKGEN: Generates the standard information required by the GMTXD.
This includes nuclide I.D., photopeak energy span, decay factors,
efficiency factors, and interference factors. Data relating up to
eight radionuclides can be entered for each geometry/shield
combination.
MTXIN: Reads information generated by DKGEN from cards onto disk.
TPKHT: Calculates information on standards for input to DKGEN. A
list of isotopes is specified and for each, the following is
20
-------
calculated:
1. peak location
2. one-third peak height
3. end points defining oeak width at one-third peak height
4. sum under one-third peak height
5. gamma efficiency or activity
GMPLT: Provides a graphical representation of gamma spectra.
GROSS : Calculates gross gamma activity from spectra.
r. Reports data in specified format.
F. System Performance
1. Data Turnaround
On a routine basis gamma matrix output is available within 24
hours of sample receipt. During an emergency situation, a batch
of 50 samples can be logged in, counted, analyzed and reported
within 6 hours. As many as 200 samples can be processed in a day.
2. Sensitivity (All Analysis)
. This summary lists the standardization of round-off, significant
figures, sensitivity, and notes to be used for all results reported.
It should be noted that in gamma spectral analysis, minimum
sensitivity is dependent upon both isotopic mixture and relative
isotope concentration as well as sample counting time. Therefore,
those values stated below for gamma isotopic results refer to low
level environmental samples. This is the reporting procedure issued
as of July 1, 1969.
21
-------
a. Gamma Isotopic Results:
Milk
Water
*
Food
Feed
Veg.'
**
**
Air
Filters
Minimum Sens.
pCi/1 or kg
Less than
100 pCi/1 or kg
1 significant figure
1 significant figure
1 significant figure
1 significant figure
1 significant figure
Greater than
100 pCi/1 or kg
2 significant figures
2 significant figures
2 significant figures
2 significant figures
2 significant figures
40-min 20-min
count count
10 20
10 20
10
50
50
Not std
sample
X
X
2 significant figures down to 1.0 pCi/m3, 1 significant figure down to
0.1 pCi/md, LT (0.1) for less than 0.1 pCi/m3
*
100-minute count
**
10-minute count
All potassium results reported as g/1 or kg sample to 2 significant
figures valid only if milk sample size exceeds 2 liters.
NOTES: LT (X) means less than (X) with X being equal to the MDA
BLANK: a) not reported because not detected; or,
b) may be present but masked by other isotopes
GSN: no reportable isotopes
As a rule, gamma isotopic results for natural vegetation are not reported
unless specifically requested. A gross gamma figure is reported for
natural vegetation as follows:
2 significant figures (cpm/kg)
Minimum sensitivity LT (500 cpm/kg)
22
-------
b. Radiochemistry Results:
*
Radiostrontium - Milk, Food , and Water
Minimum
Sensitivity
Less than 10 pCi/1 or kg Greater than 10 pCi/1 or kg pCi/1 or kg
1 significant figure 2 significant figures 89Sr = 5
90Sr = 2
*
Radium-226 - Milk, Food , and Hater
Minimum
Sensitivity
Less than 1.0 pCi/1 or kg Greater than 1.0 pCi/1 or kg pCi/1 or kg
1 significant figure 2 significant figures 0.1
Tritium - Water
'Present - 2 significant figures; minimum sensitivity 400 pCi/1
Gross Alpha and Beta - Fresh Water
Minimum
Less than 10 pCi/1 Greater than 10 pCi/1 Sensitivity
1 significant figure 2 significant figures 2 pCi/1
*
The minimum sensitivities for Radiostrontium and Radium-226 in food
are based on total diet ash samples where the ash content is about
1%. For other samples, the minimum sensitivity must be adjusted
according to the ash content.
23
-------
Gross Alpha - Salt Water, Vegetation, and Soil
Minimum
Less than 10 pCi/1 or gm Greater than 10 pCi/1 or gm Sensitivity
1 significant figure 2 significant figures 4 pCi/1 or gm
c. Gross Beta on Air Samples:
Less than 1.0 pCi/m3 Greater than 1.0 pCi/m3
1 significant figure 2 significant figures
Minimum sensitivity is equal to. that concentration which is
four times the 2 sigma counting error.
d. Present Exceptions to General Reporting Procedures:
1) Analytical Quality Control Services
All gamma results are rounded to the nearest pCi per liter
or kilogram without regard to significant digits. Strontium-89
is rounded to the nearest pCi and strontium-90 is rounded to
the nearest tenth pCi without regard to significant digits.
Potassium is reported to the nearest hundreth gram and
calcium is reported to two significant digits. Tritium is
reported to three significant digits.
2) EPA Network Data
At the present time, all results above zero are reported to
the Surveillance Data Management System using the standard
round-off procedures, but no "less than" values. A
24
-------
separate, report is sent to the regions for distribution
to the states. This separate report contains results with
"less than" values for results less than minimum detectable.
In the report sent to the Surveillance Data Management
System, no evaluation is placed on the data by SWRHL;
the numbers are reported as calculated.
25
-------
TABLE 2
ISOTOPE STANDARDS LIBRARY
ISOTOPE
NA
NA
K
K
SC
CR
MN
MN
CO
FE
CO
ZN
SR
Y
SR
ZR
ZR
MO
RU
RURH
CD
CD
SB
I
I
TEI
I
CS
I
CS
CS
BA
BA
LA
CE
CE
CEPR
ND
W
W
W
AU
RA .
NP
22
24
40
42
46
51
54
56
57
59
60
65
85
88
91
95
97
99
103
106
109
115
125
131
132
132
133
134
135
137
138
139 '•
140
140
141
143
144
147
181
187
188
198 :
226
: 239
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
01
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
02
GEOMETRIES
03 04 06 10 12 13 15 16
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
03
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
06
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
12
12 15
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12 15
12
12
12 15
12
12 15
12
12
12
12
12
12
12 13 16
12
12
TOTAL
4
6
5
6
4
6
5
6
6
6
5
5
5
6
6
6
5
6
4
6
6
6
3
7
5
6
5
5
6
6
3
5
7
6
5
6
5
6
4
6
4
8
6
6
26
-------
Standards,
Known
Response
Unknowns
Counting
System
Data
Unknown
Response
/
s
*"
X
No
Quality
Control
I
*
Basic
Assumptions
S'
Comparison
,1
Verify
Assumptions
A
-< Arrpnfahl p^
N. ? /
\.J
s >
•N
*
Systems characteristics
Standards Library
System Background
(es
• \ Rpnnrt
FIGURE 7
PROCESS FOR QUANTITATIVE GAMMA SPECTRAL ANALYSIS
27
-------
Detectors
Analyzers
Output
Tape Perforator
Typewriter
Tape Perforator
Typewriter
10
Tape Perforator
Typewriter
Tape Perforator
Typewriter
Tape Perforator
Typewriter
FIGURE 8
GAMMA SPECTROMETER SYSTEMS CONFIGURATION
28
-------
OJ
o
O)
u
10
03 6
GEOM. 1 2" Filter
GEOM. 2 4" Filter
GEOM. 10 Air Filter
GEOM. 3 Cottage Cheese
GEOM. 6 3.5 L.
1.
0.20 0.40 0.60 0,80 1.00 1,20 1.40 1.60 1.80 2.00 2.20 2,40 2.60
Energy (MeV)
FIGURE 9
GAMMA EFFICIENCY CURVE, SYSTEM 1
29
-------
r
1.065
1.67
Energy (MeV)
FIGURE 10
207Bi STANDARD SPECTRUM
30
-------
TABLE 3
,207Bi INSTRUMENT QUALITY CONTROL DATA LISTING
OATF
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
SYST
01
01 .
02
02
03
03
04.
04
05
i 05
06
06
07
07
08
08
09
09
. 10
10
PK
1
1
1
1
1
1
1
1
1
1
56
05
56
06
56
06
56
05
56
06
56
05
56
06
56
06
56
06
56
05
CHAN
.063
.803
.483
.683
.621
.305
.613
.856
.782
.320
.455
.562
.759
.351
.499
.508
.678
.204
.379
.803
01
49
50
49
49
49
49
49
50
49
49
FF
.740
.200
.684
.242
.538
.108
.592
.008
.526
.424
SUM
5501
2494
5551
2497
5446
2414
5711
2526
12332
5573
9871
4306
10481
4625
10014
4485
5538
2^58
5731
2606
RF.5
8
6
9
6
10
7
8
6
9
7
11
8
11
8
10
7
9
7
9
7
.894
.728
.321
.842
.316
.656
.807
.364
.314
.289
.251
.917
.366
.855
.064
.832
.724
.636
.041
.021
SUM2/SUM1
.45343
.44982
.44324
.44227
.45194
.43618
.44133
.44789
.44387
.45472
31
-------
Return to
Sample
Control,
Chemistry
Gamma count
10-40 min
v
Paper tape
spectrum
Type-out
(hard copy)
Gamma coding
record
Yellow copy
of
Log-in form
/Translate
/ info to
"fiamma codinc
I record
Add count
data
Keypunch
header card
Merge
Review, post
results on
hard copy
Keypunch
results
Report
NRGEN
NRCOL
FIGURE 11
SAMPLE AND DATA FLOW GAMMA ANALYSIS SYSTEM
32
-------
CD
cr
73
oo
CO
OJ
o>
3
Q»
O
o
CL
<£>
o
o
CL
GAMMA ANALYSIS CODING RECORD
SYSTEH
1
2
3
4
5
6
7
1
1
11
11
12
13
14
IS
It
17
11
IS
21
j\- 1
LOCATION CODE
PROG.
1
2
o
3
4
5
6
COUNTY
7
1
S
STATE
11
11
REGION
12
UJ
Q.
13
14
'APE NO.:
n
LOG NUMBER
15
16
17
11
19
20
DATE COLLECTED
MONTH
21
22
<
Q
23
24
YEAR
25
26
ir
o
I
27
28
29
30
ATP
PIINCHFRRY-
OTHER I.D.
LOG A.
31
31
33
j
<
(0
34
35
36
37
EVENT
36
39
40
41
42
DATE COUNTED
MONTH
43
44
<
a
45
46
a:
0
47
46
49
50
COUNT-
ING
TIME
51
52
53
SAMPLE SIZE
54
55
56
57
UNITS
51
svs
59
60
GEO .
61
62
RECT.
63
-------
MATRIX SOLUTION WITH DELETION
NO DETECTABLE NUCLIDES
51 0306 007 27 9 24
MATRIX
CE144
I 131
RU106
CS137
ZR 95
MN 54
K 40
6A140
MATRIX
I 131
CS137
98121 2 2 71 3.500 UNITS-1 3651430 16 2 9 14 14
SOLUTION WITHOUT DELETION
=-3.b75E+01
= 1.585E+01
= 5.545E+00
= 3.322E+00
=-3.348E-01
= 4.755E-01
=-2.443E-02
=-2.83lE*00
<-3.515E*01)
( 8.671E*00)
( 5.471E+00)
( 3.321E+00)
(-3.107E-01)
( 4o682E-01)
<-2.4<*3E-02)
(-1.935E+00) '
SOLUTION WITH DELETION
= 1.389E+01
= 2.814E+00
51 0208 015 27 9 24
MATRIX
CE144
I 131
RU106
CS137
ZR 95
MN 54
K 40
BA140
MATRIX
CE144
I 131
CS137
ZR 95
MN 54
( 7.599E*00)
( 2.813E+00)
98122 2 2 71 3.500 UNITS-1 0511430 26 2 9 14 14
SOLUTION WITHOUT DELETION
= 1.783E+02
= 6.479E+01
=-1.851E+00
= 4.810E*00
= 2.174E*00
= 9.294E*00
= 2.299E-02
=-1.177E«00
( 1.752E+02)
( 3.526E*01)* ;
(-1.826E*00)
( 4.808E*00)
( 2.016E*00)
( 9.149E+00)
( 2.299E-Q2)
(-8.016E-01)
SOLUTION WITH DELETION
= 1.764E*02
= 6.447E*01
= 4.775E*00
= 2.181E*00
= 9.107E*00
( 1.734E+02)
( 3.509E*01)
( 4.773E*00)
( 2.023E+00)
( 8.965E*00)
51 0544 007 27 9 24 98123
71
3.500 UNITS-1 2011430 16 2 9 15 0
MATRIX
CE144
I 131
RU106
CS137
ZR 95
MN 54
K 40
bA140
SOLUTION WITHOUT DELETION
= 6.973E*01 ( 6.869E*01) '
. .•
. -
—
=
5.505E»01
3.119E-01
1.420E*01
6.576E-01
5.038E*00
6.623E-02
1.031E+01
( 3.227E*01)
( 3.082E-01) i
( 1.420E*01)
( 6.155E-01) !
( 4.969E*00) !
( 6.623E-02)
( 7.355E*00)
MATRIX
CE144
1 131
CS137
MN b**
K 40
SOLUTION WITH DELETION
= 7.230E*01 ( 7.121E*01)
= 1.451E+01
= 6.620E-02
( 3.263E+01)
( 1.450E*01)
( 6.620E-02)
UA140 = 1.030E+01 ( 7.355E*00)
51 2316 007 27 9 2498119
71
3.500 UNITS-1 1091430 2 6
16 30
MATRIX SOLUTION WITHOUT DELETION
CE144 = 1.319E*02 ( 1.296E+02)
1 131
RU106
CS137
ZR 95
= 2.358E*01
=-1.222E»01
=-2.584E»00
= 5.938E-01
( 1.2b5E*01)
(-1.205E*01)
(-2.583E*00)
< 5.492E-01)
1
*numbers in parenthesis represent
activity at time of count.
FIGURE 13. Gamma Analysis Output Listing
34
-------
IV. AIR SYSTEM
A. • General Description
Approximately TOO air filters and 25 charcoal cartridges are
received daily for analysis. The air filters receive a sequence
of three gross beta counts and the activity is extrapolated back
to the end of collection. Extrapolated gross beta activity is
used to document trends in long-lived airborne radioactivity.
Activity at time of count is used as a screen to detect sudden
increases in gross activity. If the beta activity is above a
preset level at time of count, it is submitted for gamma analysis.
ATI the charcoal cartridges receive a gamma scan. If the gross
gamma activity is above a preset guide, then, isotopic quantita-
tion is performed. Processing of these samples follows the pro-
cedures established within the gamma analysis system description.
Part G of this section includes figures showing the flow of sample
and data.
B. Instrumentation
The counting systems consist of three Beckman (Sharp) Widebeta
counting systems. Each counter has a 5-inch-diameter thin window
(100 mg/cm2) gas flow, proportional detector which is incorporated
in a 6-inch-thick lead shield to eliminate background from environ-
mental radiation. The sample detector is operated in anticoinci-
dence with a cosmic-ray guard counter which removes the cosmic-ray
component of background.
35
-------
The systems use pure methane (99.99%) as counting gas and are
operated in the proportional region (3KV, H. V.) to provide for
both alpha and beta counting based on pulse height discrimination.
Simultaneous alpha and beta accumulation and readout are provided.
The systems incorporate an automatic sample chanqer (60 sample
caoacity) and an automatic data readout capability. Readout is by
means of IBM Model 026 Hollerith card punch.
The air filters are counted on 4-inch stainless steel planchets.
The collection data pertaining to the sample are pre-punched on
the IBM Hollerith card which is placed in the card punch in
the same sequence as the samples in the sample changer. Counting
data for each sample are then automatically punched onto desig-
nated fields on the IBM Hollerith card.
A typical system is shown in Figure 14.
C. Calibration and Quality Control
Each system is calibrated over a range of beta energies and self-
absorption. Typically, using 90Sr/90Y in equilibrium with an average
maximum beta energy of 1.40 MeV, a curve (Figure 15) of Beta
counting efficiency Vi'. sample weight can be developed. Using
a weightless standard solution deposited uniformly on glass fiber
filters, a curve (Figura 16) of beta counting efficiency as a
function of maximum beta energy can be plotted. These calibration
procedures are described in detail in Appendix C.
For large scale processing of samples, calibration data used in
36
-------
data conversion calculations must be selected based on some
assumptions made about the sample and the nuclide composition.
A filter sample averages less than 10 milligrams total of solids
(less than 1 mg/cm2) and therefore it is assumed that self-
absorption is negligible.
Figure 17 shows the average maximum beta energy for mixed fission
products as a function of time after fission. Accordingly, an
average value of 1 MeV could be assumed at any time after two
days post fission. Also shown is the maximum beta energy for
Plowshare device nuclides with a predominance of radio-tungsten
components. It is noted that the average maximum beta energy is
lower, averaging about 0.4 MeV after 10 days. A conservative
efficiency value of 45% (corresponding to an average maximum beta
energy of 0.5 MeV) is used for data conversion.
A daily instrumental quality control check is made on each system.
This involves a 2-minute count of an alpha reference source
(239Pu) and a beta reference source (90Sr-90Y) and a 10-minute
background count. Quality control charts are maintained on each
system.
D. Sample Handling and Data Flow
The routine sample and data flow for air filters is shown in
Figure 18.
The filter is received by sample control along with its field data
form (see Appendix A). The filter is removed from the mailing
37
-------
envelope and put in a clean glasslne envelope,. Receipt of the
sample is made on a posting form (Appendix A) and obvious errors
are corrected on the data form.
The collection information is keypunched in the first 24 columns of
each of three color-coded IBM Hollerith cards. The sample along with
its cards is submitted for the first beta count. The samples are
stacked in the sample changer and the first count cards placed in the
card puncher in the same order. The filters are counted for 2
minutes each and the count data are automatically punched onto
designated fields on the card. Figure 19 shows the information
fields on the Hollerith card..
The first count card is checked and if the gross beta count is
greater than 1000 counts, the filter is submitted for gamma scan
(see Section III, Gamma Analysis System). The filter is recounted
at five days after collection (after natural radon and thoron
daughter products have decayed out) and at twelve days post collection.
The filter may be submitted for gamma analysis if the 5-day count is
unusually high.
\
Special (event-related) filters are handled in a similar manner with
two significant changes. First, the filter is submitted for gamma
analysis, then, an initial beta count. If gamma analysis
indicates that natural radioactivity is negligible, the second beta
38
-------
count is made at +24 hours after the first, and the third beta
count at 5 days or less after collection. If natural radioactivity
is prominent, the normal 5-day and 12-day beta counts are made.
Second, a variety of algorithms are available for extrapolation of
beta count data to end of collection. Figure 20 shows the sample
and data flow for special (event-related) samples.
The individual count cards are submitted for data processing. The
computer programs check for a variety of data errors, calculate
the beta activity concentration at time of count, and produce a
report of these values. At the end of each month the activity is
extrapolated to the end of collection and a report of extrapolated
data is generated.
E. Data Analysis
A variety of computer programs are utilized to analyze and report
air surveillance data. These are summarized below:
AIRCK: checks the input deck for DBETA for a missing date
card, missing information on the date card, a missing header
card, an invalid punch (e.g., alphabetic character where a
numeric should be) in a count card,,or logical errors on a
count card (e.g., month collection started greater than 12, time
of count before time collection stopped, etc.). The program
. • pauses if the date of header card is in error, and it prints an
error code and the card image of any count card in error - also
the count card is selected into the alternate stacker. AIRCK
39
-------
will continue checking a card until all possible testing is com-
pleted.
DBETA: generates the Daily Air Report and has an option to
update the disk file DBTAF.
BLIST: generates a line of information for each of the count
cards found to be in error by AIRCK. This report is attached at
the end of the Daily Air Report.
GBETA: generates the Daily Gross Beta Results Report or lists
the first 19 words of records 1-999 of the disk file DBTAF.
There are no calculations performed by GBETA except to set the
column headings for the report.
GGAM: generates the Weekly Gross Gamma Report and the Monthly
Gross Gamma Report. There are no calculations performed by GGAM
and main test is to determine if the sample was quantitated.
PASS2: checks the input deck of MBETA for a missing date card,
a missing record on the disk, or logical errors in a set of count
cards (e.g., a count card is missing, time on before time off of
last valid sample for a station, etc.). The program pauses if
the date card is in error, prints an error code and the card
images of the last valid card and the last card read for any log-
ical errors found, and prints a message with the station number
for any station with no information on the disk. Once the first
error is found based on the information on a card, the next card
is read.
40
-------
MBETA: generates the Monthly Air Report.
ALTER: modifies the disk file DBTAF. There are options to;
i) add station information - name and location,
ii) delete station information - entire record
iii) change beta concentrations for last 10 days for a
station
iv) reload entire file.
DBTAF: the disk file used by the Air Surveillance Network.
It contains 1000 records of which 999 are used by the ASN
stations. Record 1000 contains the month, day, year the file
was updated. Records 1-999 contain the station number, station
name, and beta concentrations for the last 10 days.
ALGOR: provides a means to extrapolate beta concentration to
end of collection period using one of five algorithms.
1) Two Isotope Algorithm
ACTIV = AISTP + BISTP
where AISTP = (AL - BISTP * X) /W
BISTP = (A2 * Y)/ (W * Z - X * Y)
Al = Activity at time of first count used
A2 = Activity at time of second count used
W = EXP(-LAMBA * TAU1)
X = EXPC-LAMBB * TAU1) ;
Y = EXPC-LAMBB -* TAU2)
. Z = EXPC-LAMBB * TAU2)
41
-------
TAU1 = t, - t
1 c
TAU2 = t_ - t
2 o c
t.^ = time of first count used
t2 = time of second count used
t = time collection stopped
2) Known Formation Algorithm
ACTIV = A2 * (TAU2/TAU1) ** 1.2
where A2 = activity at time of second count
TAU1 = tc - tf
TAU2 = t2 - tf
tf = time of formation
tc = time collection stopped
t2 = time of second count
3) Calculated Age Algorithm
ACTIV = AL * (TAGE/(TAGE - TAU1)) ** 1.2
where TAGE = TAU2/((A1/A2) ** .835 - 1.)
Al = activity at time of first count used
A2 = activity at time of second count used
TAU1 = tl - tc
TAU2 = t2 - t-L
tc = time collection stopped
t, = time of first count used
t = time of second count used
42
-------
4) Calculated Exponent (log/log) Algorithm
ACTIV = A2 * (TAU3/TAU1) ** EXPON
where EXPON = (ALOG(AL)-ALOG (A2))/(ALOG(TAU3) - AL06(TAU2})
Al = activity at time of first count used
A2 = activity at time of second count used
TAU1 = tc - tf
TAU2 = tx - tf
TAU3 = t2 - tf
tf = time of formation
t = time collection stopped
t-j^ = time of first count used
t2 = time of second count used
5) Calculated Exponent (semi-log) Algorithm
ACTIV = A2 * EXP (-EXPON * TAU2)
where EXPON = (ALOG(Al) - ALOG (A2))/TAU1
Al = activity at time of first count used
A2 = activity at time of second count used
TAU1 = tx - tc
TAU2 = t.2 - tc
tc = time collection stopped
^ = time of first count used
t2 = time of second count used
F. System Performance
Routinely, 100 filters per day are received into the system thus
43
-------
requiring 300 counts per day. As many as 200 filters per day could
be handled. Turnaround from time of sample receipt to daily beta
report (for first count) is routinely 24 hours. During event periods,
a turnaround of 5 hours is possible for a batch of 60 samples.
Sensitivity is calculated for each individual filter. Minimum
detectable activity is defined as that activity which produces a
+ 25% counting deviation at the 95% confidence level. For a typical
routine sample, this is equal to a net activity of 50 cpm.
50 cpm x 1.00 pCi x 1 = .15 pCi/m3
cpm 350 m3
G. Charcoal Cartridges
Routine charcoal cartridges are received by sample control and are
held until 3 days post sampling before receiving a 10-minute gamma
scan. The gamma spectra are processed through PONO. If the gross
gamma count is equal to or greater than 300 cpm above background, the
spectra are processed through GMTRX (see Section III, gamma analysis
system). If the gross gamma is less than 300 cpm, a gross gamma
result is produced on the card and results reported weekly. The spectra
are reviewed in any case to confirm results.
Event-related cartridges are logged in, gamma scanned, and pro-
cessed through the normal gamma system. Figures 21 and 22 show
the routine and special charcoal cartridge sample and data flow.
44
-------
FIGURE 14.
AN AUTOMATIC LOW-LEVEL ALPHA/BETA PROPORTIONAL COUNTING SYSTEM
45
-------
WIDEBETA I
.480
.460
.440
.420
'$-
nijas
.380
.360
.340
2*^
.300
.280 i
u
33
FIGURE 15
BETA EFFICIENCY AS A FUNCTION OF SAMPLE THICKNESS
-------
o
o
70
^60
•>
50
30
20
10
0
4
a
System 1
System 2
System 3
J3_
0.5
1.0
Max. Beta Energy - MeV
1.5
2.0
FIGURE 16
BETA CALIBRATION COATED FILTER
-------
CO
0.2 MeV Max.)
\
Calculated from Hunter and Ballou
(All Beta Emitters)
Time-iDays
10
2IT
"50"
[DD~
~ZOD~
"ITJO
~ZDt
FIGURE 17
FISSION PRODUCT - AVE. MAX. BETA ENERGY vs. TIME AFTER FISSION
-------
Sample /
received, /
/repackaged,/
posted A
Collection
Information
Keypunch \
Data Cards!
Beta Count
# 1
Assign No/^ Yes
Log in
\
Gamma Scan
i
GMTRX
\
No
\Store/
\
\^
Beta
at 5,
days
f \
Isotopic
Report
(
recount
12
/
( Retain A
\in storage J
Sample Flow .
Data Flow
All..capital lettered mnemonics
represent computer code
processes.
AIRCK
MB ETA
T
I
-~5
Report
(Monthly)
Collection
Info, and
Counting Data
FIGURE 18
AIR FILTER, ROUTINE SAMPLE
AND DATA FLON
49
-------
SAMPLE IDENTIFICATION
=»=
to
4-1
CO
300
1 2 1
1 1 1
222
3 33
»A A
Q 4
355
>66
7 7 7
188
) 9 9
1 2 3
£
o
0)
4J
tO
Q
0000
4567
1111
2222
3333
5555
6666
7777
8888
9999
4 5 E 7
SO
di
C
c
—
_
c
0
B
1
2
3
5
6
7
8
9
a
il
C
O
0)
B
•H
H
1000
9 10 11 1?
Mil
2222
3333
} 555
1666
7777
8888
3993
9 10 II 12
5SC
tC
3
•
o
tfl
0
13
1
2
3
5
6
7
8
9
13
M-(
M-l
O
fl)
4J
tO
n
10
1)5
1 1
22
13
15
i6
77
18
i9
415
14-1
M-)
O
00
021
1 1
22
33
4 »
4
5 5
66
7 7
88
99
!0 21
•
iH
0
r-l
td
4-1
O
H
000
??232.
1 1 1
222
333
4 A A
4 1
555
66E
7 7 7
88E
998
22 232
COUNT DATA
5
>6
77
38
)9
1 32
4-1
O
CO
•
M-l
W
1000
3343S3E
Mil
! 222
1333
>555
>666
7777
3888
)99 9
3343531
5;
•
CO
n
0
a
1
2
3
5
6
7
8
9
37
MISCELLANEOUS
IOOOOOOOOOOOOOOOOOC
1 39 40 41 42 43 44 45 46 47 48 49 5(1 51 52 53 54 55 51
111111111111111111
222222222222222222
33333333333333333:
155555555555555555!
166666666666666666!
f 777777777777777777
1888888888883888888
I99999999999999999S
B 39 « 41 42 43 « 45 « 47 48 49 EO 51 52 53 54 55 Si
COUNT DATA
3>2
.
4J
o
00
5751
1 1
2 2
33
55
66
77
88
99
i7i8
co
4J
C
3
O
c_>
nt
4J
01
PQ
0000000
59 60 61 02 E3 M 65
1111111
2222222
3333333
5 5 5 5 5 5 i
6666660
7777777
8888888
9999999
S3 60 '. SIM '1 S5
co
4J
C
3
O
CJ
cfl
tf*
CU
r-l
00000
a 67 66 » 70
11111
22222
33333
05555
£6666
77777
88888
99999
R6 07 G8 C3 70
4J
C
3
O
u
'•H
o
x;
4-t
00
OJ
hJ
00000
/I >2 11 74 75
11111
22222
33333
5555.5
66666
77777
83888
99999
71 72 73 74 75
4-1
C
3
O
U
M-l
o
0)
CJ
*H
H
OOOCB
nu n mo
1 1 1 It
2 2 222
33333
55555
66666
77777
88888
99999
70 71 70 79 CO
FIGURE 19. AIR SAMPLE COUNTING DATA CARD
50
-------
Sample
received,^
prepackaged,
posted &
logged
I Collection
Information
Keypunch
Data Cards
Sample Flow
Data Flow
Collection in:
and counting
data
Even
Related
ctivit
Extrapolated
Report
(Daily)
FIGURE 20
SPECIAL AIR FILTER SAMPLE AND DATA FLOW
51
-------
Sample
Received
/and Posted
Gamma
^
Scan
/
s
Return to ES
Filter
Gross 8
Report
PONO
(Gross y)
I
Sample Flow
Data Flow
(Terminate
)
FIGURE 21
CHARCOAL CARTRIDGE ROUTINE SAMPLE AND DATA FLOW
52
-------
Sample
received,
'posted,
logged
Gamma Scan
Return to E
PONO
Gross Gamma
Report
GMTRX
Isotopic
Report
Sample Flow
Data Flow
FIGURE 22
SPECIAL CHARCOAL CARTRIDGE SAMPLE AND DATA FLOW
53
-------
V. CHEMISTRY DATA ANALYSIS SYSTEM
A. General Description
Radiological counting data generated for samples that require
radiochemical separation or preparation are processed by computer.
Counting, calculations, reporting, and data storage and retrieval
: '„ are described in this section. Radiochemistry procedures and
methods are fully described in the reference cited in footnote 2.
B. Instrumentation
.Instrumentation described here is mainly for heat-dried samples
for alpha and beta proportional counting and liquid scintillation
solutions for soft-beta spectroscopy.
The proportional counter is a Beckman WIDEBETA II employing a 2 1/4-inch-
2
diameter detector with an 80 yg/cm thin window. The gas flow system
uses pure'methane counting gas, (99.99% pure). Background is reduced
by guard detectors for cosmic radiation detection and 4-inch low-level
lead in all directions, lined with OFAC copper. A random access
automatic sample changer accomodates 100 sample planchets. Readout
is by teletype printer. Three systems are in operation to accomo-
date heavy sample load periods. The installation is pictured in
Figure 23.
Four Beckman LS-100 Liquid Scintillation Systems comprise the
counting facility for soft beta spectroscopy. The systems operate
at room temperature, accomodate 100 samples on a conveyor, and have
54
-------
a full three channel capacity. The systems have capability for auto-
matic calibration (by the external standard-channels ratio method)
with two separate and independent data channels for external standard
counts, and with automatic subtraction of sample counts from standard
counts. The output printer automatically displays data after each
count including channel number and conveyor number, elapsed time, 2 a
error and counts per minute. Figure 24 shows the system layout.
Radon Gas analysis is described in the SWRHL Handbook of Radiochemical
Analytical Methods. Instrumentation is illustrated in Figure 25.
There are two separate systems utilizing the Lucas scintillation cell.
The automatic sample changing system is basically a modified SHARP
LOWBETA. The Lucas cell sits on a phototube which is coupled to a
preamplifier and amplifier/discriminator for straight pulse height
discrimination detection. There is no anti-coincidence circuitry.
Readout is via line printer which identifies the cell number, counting
time, and the counts. The manual system is essentially the same with
the exception of the sample changing mechanism. Four phototubes are
incorporated in a light-tight box for simultaneous counting of four
Lucas cells.
C. Calibration and Quality Control
Daily instrumentation quality control and general calibration methods
for the WIDEBETA II systems are the same as described for the WIDEBETA
systems under section IV,Air Sampling system. More detailed descrip-
tion of preparation of standards, calibration procedures and other
related information is included in Appendix C.
55
-------
D. Sample Handling and Data Flow
All samples handled within the Technical Services Program pass
through Sample Control. Those samples requiring radiochemical
separation or preparation are identified accordingly. These are
routed through the Laboratory Operations Section after completion
of ,non-radiochemical analysis. For liquid scintillation analysis
an aliquot of the samnle is removed so that processing of the
sample for various analyses can occur simultaneously.
Counting data generated by these systems are merged with other
information and submitted for processing by computer.
E. Data Analysis
Several computer programs are used to process data, perform calcu-
lations, and generate various reports relating to radiochemical
analysis. These report data are eventually merged with other radio-
nuclide analysis data for generating other summaries and reports as
well as for storage for future reference,
RCHEM: This program performs the calculations required to find
the concentrations of 89Sr and 90Sr in environmental samples.
In order to obtain a value for the activity of each isotope, a
general coding form was devised for input information based on
two different methods utilizing the decay schemes of 89Sr and
90Sr. Copies of the coding form and description of the calcu-
lation methods are included in Appendix D.
56
-------
LIQSA: This program calculates the activity concentration of
3H and 11+C from liquid scintillation counting data. Results are
listed for editing and produced on punched card for accumulative
reporting. Calculation methods are included in Appendix D.
RADON: Calculations of volume, atmospheric condition corrections
and 222Rn concentration and listing of results are performed by
this program. Appendix D contains details of calculations.
GROAB; This program calculates the gross beta and gross alpha
activity in environmental samples. Results are listed for edit-
ing and produced on punched card for accumulative reporting.
Calculation methods are included in Appendix D.
57
-------
FIGURE 23. WIDEBETA II SYSTEM INSTALLATION
58
-------
FIGURE 24. LIQUID SCINTILLATION SYSTEMS
59
-------
cr>
o
FIGURE 25. RADON GAS ANALYSIS SYSTEM
-------
APPENDICES
.APPENDIX Page
A. MISCELLANEOUS FORMS RELATING TO SAMPLE 62
COLLECTION AND SAMPLE LOG-IN
B. SIMULTANEOUS EQUATION METHOD OF GAMMA 68
SPECTRAL ANALYSIS
C. QUALITY CONTROL AND CALIBRATION WITHIN 78
THE TECHNICAL SERVICES PROGRAM
D. CALCULATION PROCEDURES AND METHODS IN 94
RADIOCHEMICAL ANALYSIS
61
-------
APPENDIX A
Miscellaneous Forms Relating to Sample Collection
and Sample Log-in
62
-------
STATION NAME:
SAMPLE NUMBER
STATION
NUMBER
1
2 [3
DATE ON
MONTH
4
5
DAY
6
7
SAMPLE
CODE
8
TIME ON
HOUR
9
10
MINUTES
11
12
o
u
<
>
13
DATE
OFF
DAY
14
15
TIME OFF
HOUR
16
17
MINUTES
18
19
VAC
OFF
20
21
TOTAL TIME
IN HOURS
WHITE
22
23
RED
24
Remarks:
charcoal
rain
snow
MILITARY TIME
SAMPLE CODE
MID.
1 A.M.
2 A.M.
3 A.M.
4 A.M.
5 A.M.
6 A.M.
7 A.M.
8 A.M.
9 A.M.
10 A.M.
11 A.M.
0000
0100
0200
0300
0400
0500
0600
0700
0800
0900
1000
1100
12 NOON
1 P.M.
2 P.M.
3 P.M.
4 P.M.
5 P.M.
6 P.M.
7 P.M.
8 P.M.
9 P.M.
10 P.M.
11 P.M.
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
0 MO TOR FAILURE OR
MISSING FILTER
1 FIRST FILTER STARTED
2 SECOND FILTER STARTED
ASN FIELD LOG FORM
62 a
-------
PORTABLE AIR SAMPLER DATA SHEET
OFF-SITE SURVEILLANCE
| LOCATION:
|SAMPLER NUMBER
STATION
NUMBER
DATE ON
MONTH
DAY
SAMP.
CODE
TIME ON
HOUR
MIN.
VAC
ON
1 2 3
8
9 10
11 12
13
DATE OFF
TIME OFF
DAY
HOUR
MIN.
VAC.
OFF
TOTAL TIME
HOURS
14
15
16 17
18 19
20 21
22 23 24
CUBIC FT,
OFF
CUBIC FT,
ON
INDICATED
FLOW
MULTIPLY
47
48
49
50
51
52
53
54
55
56
TOTAL
CU. FT.
REMARKS:
PORTABLE AIR SAMPLER FIELD LOG FORM
63
-------
STATION,
MONTH
LOCATION
TIME ON
DATE OFF
TIME OFF
PREFILTER
DATE RECEIVED.
CHARCOAL
DATE RECEIVED
RM-11
ASN FILTER POSTING FORM
64
-------
MILK SAMPLE COLLECTION DATA
DAIRY
NAME OF RANCH NO. COWS MILKED
NEAREST TOWN TIME DATE
n f¥| O tT"l
©DATE OF MILKING p.m p.m
LOCATION CODE
CLASSIFICATION CODE
COLLECTED BY
REMARKS:
MILK SAMPLE FIELD LOG FORM (White)
WATER SAMPLE COLLECTION DATA
EXACT LOCATION
NEAREST TOWN TIME DATE
LOCATION CODE
©CLASSIFICATION CODE
COLLECTED BY
REMARKS:
WATER SAMPLE FIELD LOG FORM (Blue)
65
-------
FEED SAMPLE COLLECTION DATA
NAME OF DAIRY RANCH.
NEAREST TOWN TIME DATE,
©LOCATION CODE
CLASSIFICATION CODE
COLLECTED BY
REMARKS:
FEED SAMPLE FIELD LOG FORM (Brown)
VEGETATION SAMPLE COLLECTION DATA
EXACT LOCATION
NEAREST TOWN TIME DATE.
LOCATION CODE
©CLASSIFICATION CODE
COLLECTED BY
REMARKS:
VEGETATION SAMPLE FIELD LOG FORM (Green)
66
-------
SPECIAL SAMPLE COLLECTION DATA
EXACT LOCATION
NEAREST TOWN TIME DATE
LOCATION CODE
©CLASSIFICATION CODE
COLLECTED BY
REMARKS:
SPECIAL SAMPLE FIELD LOG FORM (Yellow)
67
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APPENDIX B
Simultaneous Equation Method of Gamma Spectral Analysis*
*From the Public Health Service Training Manual, "Radionuclide Analysis
by Gamma Spectroscopy"
68
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SIMULTANEOUS EQUATION METHOD
QUANTITATIVE ANALYSIS
I. INTRODUCTION
Many types of environmental samples, which must be analyzed routinely,
have a fairly constant radionuclide content which is limited to a
specific minimal number of nuclides. Examples are milk contaminated
with 10 day or older fallout, 30 day or older atmospheric fallout
particulates, or effluents from normal reactor operations if short-
lived nuclides are decayed out.
A convenient method for the quantitative analysis of this type of
sample is the "simultaneous equation method." This method entails a
mathematical approach for eliminating Compton interference from photo-
peaks. The only requirements for application of this method are:
1) That all nuclides present in the sample are identified
2) That a different photopeak be present for each nuclide in the
sample. This does not exclude the possibility of many over-
lapping peaks.
II. DEVELOPMENT OF METHOD
A. Interference Factors
The principle of "constant spectral shape" states that the ratio
of any portion of a spectrum to another portion is constant and
independent of the activity. A useful ratio is that of the photo-
peak channel(s) of a different nuclide to the photopeak channel(s)
of the nuclide whose spectrum is being considered. This ratio,
69
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termed an interference factor, is obtained from a standard
spectrum of the single nuclide. The significance of this
terminology will become apparent shortly.
First consider the spectrum of the nuclide Z (see Figure 1).
It is possible to express the count rate of any channel in
terms of any other channel. If channel 10 is taken as the
reference peak, the count rate in channel 20 can be written
as:
CR20 = f(io-20)CRlO
where
CR
20
= count rate in channel 10
(10-20)
interference factor
30
20
10
HIM
CHANNEL NUMBER
SPECTRUM OF NUCLIDE Z
70
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The interference factor is calculated by:
f = ^20 = 15 =0.5
10-20 CR1Q 30
thus if count rate in channel 10 of another spectrum of nuclide Z
is 50 counts per minute, the count rate in channel 20 becomes
25 cpm.
CR = 0.5 X 50 =25 cpm
B. Simultaneous Equations
Next the spectrum of a sample containing two radionuclides,
X + Y is considered. Figure 2 shows the individual spectra of
X and Y and the composite spectrum.
The net count rate of the composite spectrum for the photopeak
channel of nuclide X (Nx) can be written as:
N = X + X (1)
x x y x '
where
Xx = count rate contributed by nuclide X
to the photopeak channel of X
X = count rate contributed by nuclide Y
y to the photopeak channel of X
71
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20
10
NUCLIDE X
20 _
NUCLIDE Y
10
I
o
u
I I I i I i i i
y
i
NUCLIDES X -t- Y
10
10 15 2C
CHANNEL
SPUCTRUM OF COMPOSITE SAMPLE
72
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However, X may also be expressed in terms of Y , the count rate
contributed by nuclide Y to the photopeak channel of Y.
X = f Y (2)
y yx y ^ '
where
f = interference factor which expresses the
yx fractional contribution of the photopeak
channel of nuclide Y to the photopeak
channel of nuclide X.
combining equations (.1) and (2), we have:
NX = *x +. fyxYy.
A similar development can be done for the net count rate in the
photopeak channel of nuclide Y (N ), resulting in the equation:
N = Y + f Y
y y xy x
C. Solution of Simultaneous Equations
The two equations:
NX = *x + 'yx^x
Ny = Yy + fxyXx
are simultaneous linear independent equations containing two unknowns,
Xx and Y . The net count rates (Nx, N ) of the composite sample are
obtained from the composite spectrum, and the interference factors
(fyx, fxy) are obtained experimentally from standard spectra. These
: two equations may be solved for the two unknowns, either by deter-
minants or substitution, yielding two.new equations:
Xx = CXNX + C2Ny
Yx = C3NX + C4Ny
73
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where
C2> C3, C^ are dimensionless coefficients
D. Calculation of Activity Concentration
The activity concentrations(pCi/l) for each nuclide in a composite
sample are calculated by the equation:
X
Nuclide X pCi/1 =
Nuclide Y pCi/1 =
(eff)(Vol)(2.22)
Yy
(eff)(.Vo1)(2.22)
TABLE I, FRACTIONAL CONTRIBUTIONS
SIMULTANEOUS EQUATION METHOD
Radionuclide
131!
14°Ba
WCs
UOK
Channels
16-20
23-27
30-36
70-76
Fractional Contribution of Below
Listed Radionuclides to the Photo-
peak of Nuclides Being Assayed*
131 1
1.000
0.025
0.075
0.0
^°Ba
0.866
1.000
0.313
0.185
137Cs
0.324
0.186
1.000
0.0
"°K
0.389
0,256
0.300
1.000
*Based upon 4- by 4-inch Nal(Tl) crystal and 3.5-liter water sanrole in
Marinelli beaker
74
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III. HIGHER ORDER MATRICES
A similar set of simultaneous equations can be written for more radio-
nuclides. Consider 131I, 137Cs> 11+0Ba» and 't°K» which are found in
liquid milk samples. If these radionuclides are designated as I, C, B,
and K respectively and the net count rate (gross count rate minus back-
ground, channel-by-channel) is designated as N, the equations obtained
would be as follows:
N± = Ii+fciCc + fbiBb + fkA
Nc • f±cl±+Cc + fbcBb + fkcKk
Nb = fibli+fcbcc + Bb + fkbKk
Nk = fik^ckCc + fbkBb + Kk
where
N£ = the net count rate in the photopeak of 131I
li = the count rate contributed to the photopeak of 131I by 131I
fci = the fractional contribution of 137Cs to the photopeak of 131I
The subscripts, i, c, b, and k, or combinations thereof,,as
shown in the above equations are used to denote 1311|, 137Cs,
140Ca, and ^K respectively.
For the case being considered (131r, 137Cs, 11+0Ba, and l*oK)} the "f"
values have been determined experimentally and are presented in Table 1
These values are based on a counting arrangement using a 3.5-liter
water sample in a special container and a 4- by 4-inch Nal(Tl) crystal.
Using the data it is possible to solve these equations by the method
of determinates.
75
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The following equations are the solutions:
liil
I. = 1.034 N. -0.178 N -0.843 N, -0.152 N,
i i c b k
Cc = -0.074 N] + 1.071 Nc -0.251 Nb -0.222 Nk
B = -0.013 N -0.205 N +1.123 N -0.232 N,
b 1 c b k
Kk . = -0.002 N± -0.038 Nc -0.208 Nb +1.043 Nk
IV. COMMENTARY
The method described herein has been used for rapid assay of milk samples
with very good results. Application has been applied to other samples
with higher number of nuclides present.
The main advantage of using the simultaneous equation method for assay
of gamma spectra is its adaptability for use on a computer. This allows
for fast results from a sample. In addition, little or no preparation of
the sample has to be done.
The main disadvantage to the method is that radionuclides other than
those accounted for in the equation cannot be present if the solution is
to be valid.
76
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Also, if a significant number of radionuclides are to be considered,
the solution of the simultaneous equations becomes exceedingly diffi-
cult if not impossible without the use of an electronic computer.
In working with samples of multiple radionuclides present, several
errors may be introduced. The first consideration is that of stabil-
ity and linearity of the instrument.
If two nuclides fall in the same photopeak, various applications may
be used to try and separate them. First one should look for other
photopeaks associated with the particular nuclide. Next one may study
the half-life of the nuclides and separate them this way. If these
fail to work a chemical separation may have to be used.
In determining the "f" factors one must try to keep the geometry,
density and homogeneity of the sample media constant.
The more "f" factors that have to be introduced, i.e., more nuclides
in sample, the higher the error associated with any one value becomes.
Therefore it is imperative that good counting statistics be maintained.
77
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APPENDIX C
Quality Control and Calibration
Within the Technical Services Program
78
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QUALITY CONTROL AND CALIBRATION
WITHIN THE TECHNICAL SERVICES PROGRAM
1. QUALITY CONTROL
Quality control at the Southwestern Radiological Health Laboratory is
under the responsibility of Quality Control Services. Within the
Technical Services Program, total analysis checks and instrument per-
formance checks are carried out in cooperation with Quality Control
, Services. :
Total Analysis Quality Control
1. Milk
a. Precision - Duplicate Analysis
Fifteen milk samples per month are analyzed in duplicate
for gamma emitters (131I, 137Cs, 140Ba, "0K) and radio-
strontium (89Sr arid 90Sr). The fifteen samples are picked
at random each month and are counted for forty minutes on
two different gamma detectors in the 3.5-liter Marinelli
beaker geometry. The gamma analysis is performed using an
8x8 matrix containing lltl+Ce, 131I, 106Ru, 137Cs, 95Zr,
51*Mn, ^K, and.llt0Ba. Fifteen samples are analyzed for
strontium, but not as side by side duplicates. The samples
are run by the rapid ion exchange procedure in which EDTA
is added to complex the calcium so that strontium carrier
yield may be determined gravimetrically. (The
78a
-------
method is sensitive to calcium contamination of the final
strontium precipitate.) The samples are counted twice; once
immediately and again after about a week to allow ingrowth of
90Y and decay of 89Sr. The radiostrontium activity concentra-
tions are calculated by solution of simultaneous equations as
described in Appendix C.
The 15 duplicate results are then subjected to a statistical
test based on ranges to determine acceptable or non-acceptable
duplication.
b. Accuracy - Cross-Check Sample
One control milk sample per month is analyzed in triplicate
for gamma emitters and radiostrontium by the same methods out-
lined above. The results are reported to the Analytical
Quality Control Section and are published monthly. The re-
port gives a comparison among Public Health Service and other
participating laboratories and results are treated statistic-
ally to determine consistency of results. Since known amounts
of radioactivity were added to milk samples, comparison of
inter-laboratory results to the known results gives an esti- .
mate of bias.
2. Food
Accuracy - Cross-Check Sample
One food sample is received quarterly and analyzed in triplicate
for gamma emitters, radiostrontium, and calcium. These results
79 :
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are compared to the results obtained by other Environmental
Protection Agency Laboratories on the same sample. The data are
treated in the same manner as with the cross-check milk
samples.
3. Water
Thirteen stations of the off-site water surveillance network are
analyzed in duplicate for gross alpha and beta. The stations
selected are those which routinely show gross alpha and beta
activity. By comparing differences between duplicates over a
period of several months, an estimate of the total analysis
standard deviation can be obtained. This standard deviation can
then be used in the statistical analysis for acceptable duplica-
tion.
A more complete cross-check sampling schedule is listed in the
following table.
80
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CROSS-CHECK SAMPLING SCHEDULE (1970)
A - AQCS Cross-check
S = SWRHL Cross-check
T = Ten States Cross-check
* Superscript notation is identified on the following page
Month
January
February
March
April
May
June
July
Lake
Milk Water
Aa;Th
Ab S1
Ac
Aa S1
Ab;Th
Ac S1
Aa;Th
Sea Tap Air
Water Water Water Urine Soil Food Filter
i k 1 d 1 As
SJ Sksl Aa S1 Needed
fpr S
sk,l sj,l Af A ..
sk,l Ad,g $1
S S"^ ' "
SJ sk,l Ae $1 Ag
sk,l sj,l Ap A „
Sk>] Ad S1 . . A9
August Ab S1 Sk)1 SJ' A "
September Ac;Th: : :Sj Skjl Ad'9 SP .
October Aa S1' Sk'P SJ'j1 AP
November AbTh Sk>1 Ae SP A^
December Ac S1 Sk>1 SJ''P A "
81
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a. Milk prepared from powdered milk, 131I, 137Cs, 89Sr, 90Sr, as
added activity.
b. Milk prepared from pasteurized milk; 131I and 89Sr as activity.
ll+0Ba will be added to (a) or (b) depending on its availability,
but not more than four times a year.
c. Milk prepared from pasteurized milk, no activity added.
d. Determination of gross alpha and beta requested, specified
radionuclides optional.
e. Determination of specific radionuclides requested, gross alpha
and beta optional.
f. One blank and one spiked to 137Cs.
g. 239Pu - spike.
h. Samples are prepared in duplicate (the activity of one sample is
approximately 10% greater than the other) from milk powder and will
contain 0 - 100 pCi/1 of 131I, ^°Ba, 137Cs, 89Sr, 90Sr, ^K.
i. Two samples per month will contain 0 - 100 yg/1 of natural uranium.
,j. One sample per month will contain 10 - 100 fCi/1 of 239Pu (sample
i
frequencies may increase or decrease proportional to the total
number of samples analyzed.)
k. Two samples per month will contain 5 - 50 pCi/1 of 230Th.
1. Two samples per month will contain 400 - 3000 pCi/1 of 3M.
82
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II. CALIBRATION
A. Primary Calibration; Gamma Spectrometers
The primary system set up at the laboratory for the calibration of
gamma sources is a 4-inch well crystal with a 1-inch bore detector
system connected to a TMC 400 channel analyzer. On this system gamma
efficiency versus energy curves have been established using AQCS and
NBS standards. The best standards for this curve have been found to
be single peak nuclides, or at least nuclides where coincident gamma
emissions and sum peaks are absent. The calibration procedure utilizes
a "manual limits" program devised specifically for the purpose of
obtaining efficiencies rapidly by hand or on the computer. In this
x ',• manner, one, can calibrate nuclides whose decay schemes are accurately
known and do not have coincident gammas. Or, one can check standards'
purchased from commercial suppliers to.see if the activity statement
. on the certificate is correct.
B. Procurement of Standards
Two classes of radionuclides are utilized; standards and sources.
The standards are nuclides which have undergone some sort of primary
standardization. Standards are obtained from. NERHL (AQCS), National
Bureau of'Standards, Radiochemical Centre (Amersham), and from other
suppliers in special instances. The standards are always checked on
our calibration well crystal. The accuracy of the quoted disintegration
rate on the standard certificates varies from about 1 percent to 5
percent, usually 2 percent or 3 percent. Sources, i.e., uncalibrated
radionuclides, are bought from any supplier that sells radionuclides.
These sources are calibrated on the well crystal. For nuclides for
83
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which there is no previous calibration and whose decay schemes do not
exhibit any uncluttered or coincidence free gamma emissions, there will
be some error associated with the calibration that cannot be assessed.
B. Preparation of Counting Geometries
After calibration of a source, or after a standard has been checked for
accuracy, aliquots are taken from the standard and prepared in a selection
of ten geometries. (The geometries counted vary with the program.)
\ .Careful attention is paid to the chemical composition of the original
'radionuclide solution whenever it is necessary to perform dilutions.
When possible, the exact chemical composition (acids, bases, carriers,
complexing agents, reducing or oxidizing agents) is carried through.
The geometries are: two-inch planchet, four-inch planchet, eight- by
ten-inch filter, 250-ml plastic container., 400-ml plastic container,
3.5 liters in a Marinelli beaker, 3.5 liters in a cubitainer, 1-liter
cubitainer, 400-ml soil container, and ion exchange resin. Activity
is pipetted directly onto filters in the two-inch planchet, four-inch
planchet, and the eight- by ten-inch filter. The activity solution is
air dried, if possible, and if heat is necessary, it is kept to a
minimum. The eight- by ten-inch filter, with activity on the sampling
area, is placed in a glassine envelope, folded in thirds and wrapped
around the four by four crystal with a rubber band for counting. The
250-ml and 400-ml geometries are prepared by pipetting activity into
solutions which can contain the same reagents as the original radionuclide
solution, with the exception of certain organic solvents, since the
84
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containers are plastic. Since the Marinelli beakers are aluminum,
one cannot add strong acids or bases without affecting the container
adversely. Plastic liners are added inside the Marinelli beakers
to avoid contamination, and specific beakers are used for standards.
A complete step-by-step procedure for standards preparation is
described under the next two sections.
85
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PROCEDURE FOR
PREPARATION OF GAMMA STANDARDS
PURPOSE:
To prepare a standard of a gamma emitting radioisotope in all geometries,
with enough gamma radiation present to allow the least efficient geometry
to be counted for ten minutes (this quantity is calculated to be 1 x 10s
gamma emissions per minute), providing a spectrum with less than 1% error
due to counting statistics.
Materials and equipment:
1. A standard solution of the gamma emitting isotope to be prepared.
2. Containers for each of the geometries used.
.a. 01 - 2-inch planchet
; '.. b. 02 - 4-inch planchet
c. 03 - 400-^ml plastic container
d. 06 - 3500-ml Marinelli beaker (plastic lined)
e. 12 - 250-ml plastic container
f. 15 - 1000-ml cubitainer
g. 16 - 250-ml resin
h. 17 - Soil sample in 400-ml plastic container
3. Filter papers to fit 2-inch and 4-inch planchets.
4. Carrier solution of the same concentration and chemical form
as that of the radioactive standard to be used.
5.. Glass Lambda pipettes for direct dilution of the concentrated
standards.
6. Eppendorf pipettes for quantities taken from diluted standard
solutions.
86
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7. Spray adhesive for spraying planchets to make filter paper
adhere.
8. Distilled water.
Procedure:
1. Calculate the quantity of a given concentration of standard
needed to provide 100,000 gamma emissions per minute at the time
the standard is preoared.
a. Obtain the calibration date, time and activity of the standard
to be used. If the time is not stated, assume it to be
1200 hours,
b. If the activity is given in microcuries, convert the
value to disintegrations per minute. (lyCi = 2.22xl06
dpm).
c. Consult the book of radioactive decay correction factors
to find the half-life of the isotope to be used, and the
unit time interval (hours, days, months, etc.) used in
the table.
d. Calculate the time lapse, in terms of the units used in
the decay chart, between the date of calibration and the
time the standard is prepared.
e. Find the correction factor in the table under the time
interval calculated from step d.
f. Obtain the gamma factor from the radioisotope manual.
The gamma factor is the number of gamma photons emitted
87
-------
per disintegration.
g. Multiply the activity in dpm per ml times the decay factor
times the gamma factor in gammas per disintegration to give
the activity of the standard in gammas per minute per ml at
the time the standard is prepared.
h. Calculate any dilution of the standard (if necessary) to
provide approximately 1 x 105 to 1 x 10° gammas per minute
per ml and make necessary dilution. If the dilution is
made from'the original stock, use a glass lambda pipette;
if it is made from previously diluted stock, use an Eppendorf
pipette and allow for the bias marked on the pipette. Use
the same carrier to make dilute standards as geometries,
(see preparation of carrier for geometries, parts a and b
of next section).
2. Preparation of the standard in each geometry.
a. The chemical form of the isotope to be used is on the
standard certificate. (Most are in the form of a chloride
salt of the metal isotope in a dilute HCL solution.)
Example:: 106Ru; 95 ug/g sol. in a 1 N_ HCL.
b. Use the appropriate stock carrier solution diluted
1 to 100 and a quantity of acid (if needed) necessary
to give a final dilute concentration as specified on the
standard certificate.
c. Add the prepared dilute carrier solution (using graduated
cylinder) to each of the geometries 03, 06, 12, and 15,
-------
to the volume specified.
d. Add the previously calculated quantity of standard to each
of the geometries listed in part c., using a glass lambda,
or Eppendorf pipette as needed, and seal with a cap or lid.
e. Spray adhesive on the inside of each planchet, let dry
about two minutes, then place a filter paper disk in each.
f. Deliver the standard directly to the filter paper in a
uniform pattern over the entire surface of the paper and
let dry in air.
g. Use the same procedure for the 17 geometry as the planchets
(01 and 02), delivering the activity directly to the surface
of the soil. Be sure not to invert or shake the soil after
preparation.
h. Place the dried planchets in plastic petri dishes with lids,
and seal with tape. Also seal the lids on the plastic con-
tainers.
89
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PROCEDURE FOR
PREPARATION OF BETA COUNTING STANDARDS
PURPOSE:
To prepare standard solutions of known activity of ,90Sr - 90Y in
equilibrium, 10,000 dpm/ml as 9°'Sr; and known activity of standard
solution of 89Sr, 200,000 dpm/ml. Solutions will contain varying
amount of solids using stock solution of Sr(N03)2.
Standard Preparation:
a. Pipette known amount of Sr(N03)2 (see charts) into 50-ml
centrifuge tube.
b. Add known amount of activity to same 50-ml tube (see charts).
c. Add 10 ml of distilled or deionized H20.
d. Add 2 ml of concentrated NH^OH and swirl to mix well.
e. Add magnetic stir bar and while stirring, slowly add 10 ml
of 3N. Na2C03 to precipitate the Sr as SrC03, and stir well
for 5-10 minutes to insure complete precipitation of the Sr.
f. Centrifuge the sample and discard the supernate.
g. Wash the precipitate with 10-15 ml of distilled H20, stir
well to insure complete washing, then centrifuge sample and
discard supernate.
h. Repeat step (g) and save the precipitate.
i. If the sample is to be counted as SrC03, transfer the precipitate
to previously weighed planchet. Evaporate to dryness slowly on
low heat to prevent spattering and loss of sample.
j. When sample is dry, cool, weigh, and submit for beta counting.
90
-------
90 Sr -90Y Separation:
a. If the separation step is necessary, ta,ke the precipitate from
step (h) in standard preparation and proceed as follows;
b. Dissolve the SrC03 precipitate with. 5.0 ml of 3N. HN03 in the
50-ml centrifuge tube.
c. Add 30 ml of fuming HN03 and, while stirring with magnetic
stir bars, cool in ice bath until very cold.
d. When cold, centrifuge sample and decant supernate into 250-ml
beaker (.supernate contains90Y) and save.
e. Dissolve precipitate with 5.0 ml H20 and repeat steps (c) 'and
(d), combining the supernates in the 250-ml beaker; record time
of decantation as beginning of Y-ingrowth.
f. Evaporate the combined supernates to small volume and transfer
to planchet with 3N_ HN03. Evaporate to dryness, slowly to pre-
vent spattering and loss of sample, and count for 90Y. (May
be necessary to flame planchet to insure complete dryness.)
g. Transfer the precipitate from the centrifuge tube to a weighed
planchet with h^O, evaporate to dryness, slowly to prevent loss
of sample through spattering, and submit for Sr count.
NOTE: The SrC03 is better to work with on the planchet than Sr(.N03)2
as you can distribute the sample more uniformly and get better
counting statistics. The Sr(N03)2 is more apt to spit small bits
out of the planchet.
Magnetic stir bars are small, 3/8 or 1/3 inch, Teflon-coated
rod-shaped magnets.
91
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CHART A
(SR-Y)90 IN EQUILIBRIUM FOR GROSS BETA EFFICIENCIES
1.0 ml per sample at 10,000 dpm/ml
as Sr90
SAMPLE
NO.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
mq Sr
ADDED
0
20
40
60
80
100
120
140
160
180
200
220
240
260
280
300
ml of Sr
(20 mg. Sr/ml.)
ADDED
0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
ADDED
ACTIVITY
(Sr-Y)90
mg SrC03
RECOVERED
92
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CHART B
89Sr 'EFFICIENCY STANDARDS
1.0 ml per sample at 200,000 dpm/ml
SAMPLE
NO.
1
2
3
4
5
mg Sr
ADDED
0
20
40
60
80
1 i
•
ml of Sr
(20 mg Sr/ml )
ADDED
0
1.0
2.0
3.0
4.0
ADDED
ACTIVITY
89-Sr
mq SrCO3
RECOVERED
CHART.C
Sr-Y STANDARDS FOR Sr-Y SEPARATION
SAMPLE
NO.
1
2
3
4
5
mg Sr
ADDED
0
20
40
60
80
ml of Sr
(20 mg. Sr/ml.)
.ADDED
o.
1.0
2.0
3.0
4.0
ADDED
ACTIVITY
89 (Sr-Y)
mg SrCO 3
RECOVERED
93
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APPENDIX D
Calculation Procedures and Methods
in Radiochemical Analysis*
*For greater detail, refer to "Handbook of Radiochemical Analytical
Methods," F. B. Johns, SWRHL-11, March, 1970
94
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RESOLUTION OF STRONTIUM-89 AND STRONTIUM-90
IN ENVIRONMENTAL MEDIA BY AN INSTRUMENTAL TECHNIQUE*
The beta emissions of 89Sr and 90Sr are resolved by observing the
ingrowth of the 90Y and decay of 89Sr. The ratio of count rate of
the 90Sr and the ingrown 90Y to that of the parent 90Sr at any time
is predetermined. Two measurements of the total radiostrontium
fractions are made at an interval of 7 to 14 days. Relating this
ratio and the decay factor for 89Sr with these two measurements,
two equations can be set up and solved simultaneously to express
the individual count rate of the two strontium isotopes. The count
rate of the 90Sr is corrected for self-absorption losses by relating
the overall detection efficiency of 90Sr to that of 90Y an energetic
beta emitter with no sample absorption losses at the thickness studied.
This technique differs from conventional methods in that neither addi-
tional chemistry nor the use of absorbers is required as a differen-
tiating tool.
Principle of Method
The design of this technique is based on the decay characteristics of
the two strontium isotopes, and on the premise that the strontium
fraction produced by the radiochemical method be free of all other
isotopes.
\ • :
Since 28-year 90Sr:decays into 64-hour 90y the relationship of this
*Condensed version of paper of same title by R. J. Velten. NUCL. INSTR.
METHODS, 42, 169 (1966)
95
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parent-daughter combination to the parent at any time is a known
function of time, with a count rate ratio of unity at the time of
purification and gradually approaching 2 plus. Also, since 50-day
89Sr ,has no radioactive daughter, its activity decreases in accordance
with its half-life.
The combined effect of self-absorption and the detection efficiency
of 90Sr for a thickness of less than 5 mg/cm2 is measured in relation
to the detection efficiency of 90Y , an energetic beta emitter with
no self-absorption losses below this thickness. The 90Y efficiency
can be accurately and precisely measured. A calibrated 90Y source
need not be used to determine this relationship. A 90Sr solution is
purified by removing its 90Y daughter by an acceptable radiochemical
procedure. The final time of 90Y separation is noted as the 90Sr
sample is prepared for counting. This preparation is counted repeat-
edly under identical geometrical conditions over a 2-week period,
with more frequent observations taken during the first 4 days. The
observed count rates are plotted against the various time intervals
after the 90Y separation. A curve can then be fitted either by eye
or, more exactly, by the least squares technique.
The count rate of 90Sr fraction at any time after 90Y separation
can be expressed as
ct = fz + gz Cl-e"U)
where: ct = count rate at time t
z = dpm 90Sr
96
-------
f, g = efficiency of 90Sr and 90Y, respectively
A = decay constant of 90Y
t = time interval from 90Y separation to time
of count
From the observed data points, fz and gz can be solved by a linear
least squares technique by expressing 1-e as the abscissa and the
observed count rates as the ordinate.
Dividing both sides of the equation by fz, the count-rate ratio of
90Sr plus 90Y to the parent 90Sr at any time is determined,
£= 1 +9/f (l-e'Xt) = At
and g/f is the ratio of the 90Y to 90Sr efficiencies. In order to
quantitate the 90Sr activity, either f or g must be determined. Of
the two, g is more desirable to measure because of the high beta
energy of 90Y and the negligible self-absorption. The efficiency,
f, can then be calculated from the ratio g/f and the efficiency g.
Knowing the 90Sr-90Y count-rate ratio, ct/fz, at any time, T, and
the decay factors of 89Sr hereafter defined as At and Bt, respectively,
and by counting a total radiostrontium fraction twice at a sufficient
time interval, the count rate of each of the strontium isotopes can be
determined simultaneously.
Cl = Alx + B1Y
C2 = A2x + B2Y
97
-------
where: x = cpm 90Sr
y = cpm 89Sr
A1,A2 = 90Sr decay and ingrowth factors at Tj_ and T2
Bl'B2 = 89sr decay factors at Tj and T2
C1,C2 = observed count rates at 1^ and T2
All terms are known except x and y. Solving simultaneously
D-I Co - BoCn
= cpm
9°S
y = 1 - 1* = 2 - 2* = cpm. 89Sr
Bl B2
The disintegration rate of each isotope is then determined by
dividing its individual count rate by its respective counting
efficiency.
Since the 90Sr beta emissions are seriously affected by sample thick-
ness, the ratio Afc should be determined from a sample weight nearly
equivalent to that produced by the radiochemical procedure.
A computer code, based on the above theory, is used routinely for
solving for the 89Sr and 90Sr concentrations. The two-step equations
on the followina page are used in the computer code.
98
-------
STRONTIUM-90 CALCULATION
STEP 1
pCi 9°Sr/l
or = M_[B] _[C] [DP . x 1
qnc , , [1 + (E)(F)J (A) - D + (G)(H)J (C) (2.22)(I)(J)(K)(L)
pCi 90Sr/gm ash
A = Decay ;of 8'9Sr from the time of collection to the time of the first count.
B:= Net counts per minute of total strontium on second count.
C = Decay of 89Sr from .the time of collection to the time of the second count.
D = Net counts per minute of total strontium on first count.
E =' Ratio of the 90Y/90Sr counting efficiencies on the second count.
F = 90Y: ingrowth from the time of separation to the time of the second count.
6 = Ratio of the<90Y/90Sr counting efficiencies on the. first count.
H = Ingrowth of 90Y from time of separation to time of first count.
I = Counting efficiency of 90 ^r.
J = Chemical yield of strontium.
K = Absorption factor for 90Sr
. L = Sample volume in liters or sample weight in grams.
STEP 2 ' . . .
pCi 89Sr/l
or - (A) - [1 + (B) (C)] (D) 1
E X (FJ (G) (H) (I) (2.22)
i 89Sr/gm ash
A = Net counts per minute of total strontium on the first count.
B = 90Y ingrowth from separation to first count.
C = Ratio of the 90Y/90Sr counting efficiencies on the first count.
D = Net cpm of 90Sr (determined by calculation).
E = Decay of 89Sr from time of collection to the time of first count.
F = Absorption factor for 89Sr.
G = Chemical yield -of strontium.
H = Counting efficiency of 89Sr.
I = Sample volume in liters or sample weight in grams.
99
-------
CALCULATION OF
STRONTIUM-89/STRONTIUM-90 IN LIQUID SAMPLES*
Calculation
where (A)
(B)
(C)
(net cpm)
(A)(.B)(C)(D)(E)(F)
recovery of strontium carrier,
recovery of yttrium
counting efficiency in £^. for yttrium-90 counted
carrier free in a 2-inch^chameter stainless steel
planchet.
(D)
(E)
(F) =
: sample volume in liters
;. correction factor for yttrium-90 ingrowth (1-e" ),
where t is the time from tj to t2
correction factor for yttrium-90 decay (e"A ),
where t is the time from decantation of yttrium-90 supernate
to the time of counting.
Strontium-89: Pci/l =
•where (A)
(A)(B7
counting efficiency in
.
DC]
for strontium-89 as
strontium nitrate mounted in a 2-inch- diameter
stainless steel planchet
(B) =
correction fa.ctor for strontium-89 decay (e~ ),
where t is the time from sample collection to the
time of counting,
*This calculation was used for the nitric acid separation method. It
is still used, although much less frequently than the calculation method
as described by Velten.
100
-------
(C) = net cpm of "total radiostrontium",
(D) = recovery of strontium carrier,
(E) = volume of milk sample in liters,
(F) = self-absorption factor for strontium-90 as
strontium nitrate mounted on 2-inch-diameter
stainless steel planchet,
(G) = strontium-90 concentration in pCi/1,
cpm
(H) = counting efficiency in -^—.for strontium-90 as
pC i
strontium nitrate mounted in a 2-inch-diamater
stainless steel planchet.
(I) = counting efficiency in --^ for yttrium-90 counted
pCi
carrier free in a 2-inch stainless steel planchet,
(J) = correction factor for yttrium=90 ingrowth (l-e"A ),
where t is the time from the last decantation of
HNOs from the strontium nitrate precipitate to
the time of counting.
101
-------
CALCULATION OF
STRONTIUM-89/STRONTIUM-90 IN SOLID SAMPLES
Calculation
Strontium-90:
where (A)
(B)
(C)
pCi/g ash =
(net cpm)
IAKBKCKD7TW7
recovery of strontium carrier,
recovery of yttrium,
counting efficiency in BSUL^ f0r yttrium-90 counted
pCi
carrier free in 2-inch-diameter stainless steel planchet
(D) =
(E) =
(F) =
-At,
weight of ash sample in grams,
correction factor for yttrium-90 decay (e"Al*),
where t is the time for the decantation of the
yttrium-90 supernate to the time of counting,
correction factor for the degree of equilibrium
attained during the yttrium-90 ingrowth period
(1-e ), where t is the time from start of the
ingrowth period until the time of decantation of
yttrium-90 supernate.
1
(C)
Strontium-89: pCi/g ash = /AwB\
where (A) = counting efficiency in ^t^. for strontium-89 as
pCi
strontium nitrate mounted on a 2-inch-diameter stainless
steel planchet
(B) = correction factor for strontium-89 decay (e~ '
whore t is the time from sample collection to the
time of counting,
(C) = net cpm of "total radiostrontium",
102
-------
(D) = recovery of strontium carrier
(E) = weight of ash in grams,
(F) = self-absorption factor for strontium-90 as
strontium nitrate mounted on 2-inch-diameter stainless
steel planchet,
(G) = strontium-90 concentration in pCi/g ash,
(H) = counting efficiency in ^-. for strontium-90 as
pCi
strontium nitrate mounted in a 2-inch-diameter stainless
steel planchet
103
-------
PUNCHED BY.
SYSTEM
1st COUNT
2nd COUNT
PAGE 1 OF 2
RCHEM CODING RECORD - Sr CALCULATIONS (SHEET 1)
i
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
PROGRAM
AND
LOCATION CODES
i
10
11
13
13
U
LAB NO.
15
U
17
11
19
20
COLLECT.
DATE
21
77
21
24
U
M
77
If
19
X
I COMP |
n
LAB NO.
D
0
14
13
It
a
COLLECT.
DATE
M
»
40
41
41
41
44
41
46
47
ASH
WEIGHT
U
49
30
31
32
31
ASHING
ALIO.
34
33
54
37
il
AMOUNT
H20
ADDED
39
60
61
62
61
64
63
66
67
61
69
70
71
72
71
74
73
76
77
71
79
n
-------
o
-Pi
O>
RCHEM CODING RECORD - Sr CALCULATIONS (SHEET 2)
i
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
SAMPLE
SIZE
(1.)
t
ALIO.
(Lorg.)
PLAN.
WT.
(g.)
10
11
n
Sr COUNT (TCA) OR
1st COUNT (IXC RAPID)
DATE
n
14
15
16
17
U
19
X
LGTH
21
22
21
COUNTS
24
25
26
27
21
BG
29
10
Y COUNT (TCA) OR
2nd COUNT (TSC RAPID)
DATE
11
n
a
14
15
M
37
•
LGTH
j>
40
41
COUNTS
41
4]
44
4]
46
BG
17
41
T, BEGIN IGP
BLK. (IXC-RAR)
19
SO
51
57
51
54
55
M
Tz END IGP OR
SER TIME
(IXC-RAP.)
57
51
5»
60
61
62
61
64
ADD
65
66
67
REC
61
69
70
Co
71
72
n
74
73
»
77
71
n
ta
-------
CALCULATION OF LIQUID SCINTILLATION RESULTS
A. Tritium:
Tritium results are reported in units of picocuries per liter of sample
water. The two sigma counting error is also reported for each result
in picocuries per liter.
1. Result
G - B
E x VxDx 2.22
G = sample counts per minute from counter printout
B = counts per minute of blank (bkg.) sample
E = counting efficiency = standard cpm - blank cpm divided
by the known dpm of tritium in the standard
V = volume of sample water, in liters, contained in the
counting solution (usually 0.005 liters)
D = dilution factor = original volume divided by final
total volume. (If sample water was diluted with
distilled water prior to counting.)
2.22 = dpm per picocurie
2. Error Calculation
~\ / 4-
2V Tr + TR
E(pCi/l) C B
E x V x D x 2.22
T« = sample count time
Tg = blank (bkg.) count time
3. Example Calculations
(a) Result
G = 10.08 cpm
B = 6.61 cpm
105
-------
3H =
E = std, cpm - bkg. cpm
std. dpm
E = 3676.6 cpm - 6.61 cpm = 0.222
16.520 dpm
V = .005. liters
D = 1 (water was not diluted)
G - B
E x V x D x 2.22
3u _ 10.08 cpm - 6.61 cpm = 3 47 nr,-
0.222 cpm x .005 liters x 1 x 2.22 dpm .00246 = 141° £kL-
dpm pCi liter
(b) Error
TG = sample count. time-= 100 min.
T = blank count time = 100 min.
B
T T / 10.08 cpm + 6.61 cpm
E = 2V G B = 2^ 100 min. 100 min.
E x V x D x 2.22 0.222 x.005 x 1 x 2.22
E = .815 = 330 pCi
.00246 liter
ANSWER = 1410 ± 330 pCi/liter
4. Standard Decay
Tritium has a half-life of 12.26 years. The decay in activity of the standard
sample must be taken into account when calculating the counting efficiency. To
avoid significant errors, the standard dpm should be recalculated approximately
every 90 days.
106
-------
B. Carbon-14:
The calculation and reporting of carbon-14 results are essentially the same
as for tritium. The only basic differences are: no dilution factor appears
'in the calculation, and the.volume must be determined independently for each
sample. Carbon-14 results are reported in units of picocuries per liter of
carbon dioxide at standard conditions.
1. Result Calculation
= G - B
E x V0 x 2.22
E = efficiency
VQ = volume carbon dioxide counted
2.22 = dpm per picocurie
2. Volume Calculation
For purposes of calculation, it is assumed that carbon dioxide behaves as an
ideal gas. The volume of an ideal gas varies proportionally to the absolute
(Kelvin) temperature and inversely proportional to its pressure in atmospheres.
In carbon-14 analysis a small volume of carbon dioxide gas is trapped in a
bottle and reacted with a solubilizing agent. The temperature, pressure, and
volume of the gas may vary from sample to sample and, therefore, must be
calculated in terms of a standard set of conditions. These standard conditions
are: temperature = 0°C (273° K), and pressure = 1 atmosphere (760 mm). The
107
-------
formula for calculating the carbon dioxide volume at standard conditions
is as follows:
vn = v x P x 273° K x .001
. . 760 mm T
.001 = converts milliliters carbon dioxide to liters carbon dioxide
V0 = liters of carbon dioxide at standard conditions
V = volume of carbon dioxide (in milliliters) trapped in bottle
P = pressure in millimeters of carbon dioxide trapped in bottle
T = Kelvin temperature of carbon dioxide trapped in bottle
273°K = "standard temperature"
760 mm = "standard pressure"
V, P, and T (in C°) are obtained from a data sheet supplied with each
group of samples.
Five milliliters of solubilizing agent, "hyamine 10-X," are placed in each
bottle used to trap carbon dioxide. This amount of "hyamine" will react with
a maximum of 4.5 millimoles of carbon dioxide. At standard conditions, 4.5
millimoles are equivalent to a volume of 0.101 liters. Therefore, V° can
be no greater than 0.101 liters. If the above calculation (formula B., 2)
yields a V0 greater than 0.101, the, 0.101 liter is substituted for the
calculated value.
108
-------
3. ' Example Calculation
(a) Carbon dioxide volume
V = 200 ml
P = 179 mm
T = 24.5°C = 297.5°K
- * -00'
V = .043 liters
0
(b) Result
p oc Q/I c 4772 cpm - 24.96 cpm
G = 26.84 cpm E = - dpm - }L
B = 24.96 cpm V = .043 liters
0
2.22 = dpm/pCi
n»c _ G - B
E x V x 2.22
o
11+f _ 26.84 cpm - 24.96 cpm 1.88 -, pCi
^^ x 043 liter x 2 22 ^M " -0604 " liter C02
dpm ^ pCi
(c) Error
/G _jT
oY T~ + Tn TV = 100 min.
E =
E x V x 2.22 TR = 100 min.
0 D
109
-------
-r/26.84 , 24.96
2 YTOO"
F 00 100 = 1.44 9. pCi
.633 x .043 x 2.22 .0604 " ^ liter C02
ANSWER = 31 pCi/liter ± 24 pCi/liter
= 3.IE01 pCi/liter 2 sigma = 2.4E01
Frequently, several a]iquots of the same carbon-14 sample are analyzed.
If more than one aliquot is counted, the two sigma counting error is
computed using the formula:
E .
- (EX)2
N - 1
where
X = carbon-14 result computed for each aliquot
in pCi/1
N = number of different aliquots
110
-------
LIQUID SCINTILLATION CODING FORM
i
2
3
4
5
t
7
1
1
11
11
12
13
14
IS
U
17
IS
11
20
Location Code
1
0
o
K.
0.
t
G
o
STATE
10
11
REGION
11
UI
f
13
^
14
Log
Number
15
16
17
18
19
JO
Date Collected
MONTH 1
11
11
1
13
24
YEAR
15
M
HOUR
17
18
29
30
Other ID.
31
31
33
34
35
36
37
Event
38
39
40
41
41
U
SAMPLE T>
43
Sample Size
VOLUME
COUNTED
ml
44
45
46
47
48
PRESSURE
mm
or
INITIAL
VOLUME
«
50
51
51
53
TEMP.,°C
or
DILUTED
VOLUME
54
55
56
57
58
Counts per Minute
BACK
GROUND
59
60
61
61
63
STANDARD
64
65
66
67
68
69
70
71
SAMPLE
71
73
74
75
76
77
78
79
1 MULT. ALIQUOT |
80
-------
222
"*Rn CALCULATIONS
1. Total pCi radon determined as follows;
Rnt = (A) x 1 x 1
[B]
A = Total net counts
B = Count time in minutes
C = Cell factor: Total efficiency of gas system plus radon
cell units of cpm/pCi
D = Percentage of Xe carrier placed in cell expressed as
decimal percent
Rnt = Total pCi radon
2. Determine volume of gas sample:
V2 = V x P1 x T2
P2 T]
VT = ml of sample put in gas rig
P-] = Barometric pressure in lab, mm mercury
P2 = Barometric pressure at sampling location
T1 = Lab Temperature (°C + 273.1) coded in °C
T2 = Mean annual T at sampling location (°C + 273.1)
3. Obtain pCi/1 of radon at time of lab analysis:
Rn = Rnt
V2
4. Correction for decay from mid-point of collection to lab analysis
\
Corrected Rn = (Rn) C .693t
3.825
112
-------
PUNCHED BY.
SYSTEM
.TAPE NO.
DATE
RADON 222 ANALYSIS CODING FORM
i
2
3
4
5
6
7
8
9
K>
11
12
13
14
15
16
17
18
19
20
SMPL.
NO.
i
2
1
COLLECTION
DATE 1
IcsEnnaniacznl
10
11
n
13
14
15
M
PRES.
17
It
1*
N
TEMP.
21
22
21
24
25
26
COUNTING DATA
DATE
MO
27
M
DA
»
M
YR
n
12
HR
n
14
MN
15
M
17
PRES.
31
1»
40
41
TEMP.
42
43
44
45
46
17
VOL.
41
4»
50
51
12
/
53
o
54
Ae
55
56
17
COUNT
TIME
51
J9
60
61
a
NET
COUNT
61
64
65
66
67
61
-------
GROSS ALPHA AND BETA CALCULATIONS
1. Alpha or Beta Activity Concentration
(EFF)(2.22)(VOLUME)
2. Counting Efficiency - Alpha
Effa = 0.230, X = 0
Effa = antilog[ -0.4245 log (x) - 0.2896], X>0
where:
Effa = alpha counting efficiency, cpm/dpm
X = sample weight in milligrams
The variation in alpha counting efficiency among the three systems is
assumed to be negligible for gross alpha analysis.
The table below compares the planchet weight, x, in mg. to the observed
alpha counting efficiency, Eo, and the theoretical counting efficiency,
Xmg
0
10.0
18.5
54.5
89.5
181
278
366
622
Eo
0.230
0.197
0.147
0.097
0.080
0.064
0.048
0.042
0.026
Et
0.230
0.193
0.148
0.094
0.076
0.057
0.048
0.042
0.033
114
-------
3. Counting Efficiency - Beta
The following equation describes the average beta counting efficiency
(cpm/dpm) for the three Beckman Widebeta II systems as a function of
sol ids weight:
Eff = (425 - .155x)/1000
where Eff = cpm/dpm
X = net solids wt., mg
The difference in counting efficiency among systems is negligible.
115
-------
GROSS ALPHA AND BETA ANALYSIS CODE RECORD
SYSTEM
1
2
3
4
5
6
7
8
9
10
11
12
13
14
IS
16
17
18
19
20
Program and Location
PROG
1
2
CITY
COUNTY
ST
0
11
R
12
TYPE
13
4
Lab No.
15
6
7
8
9
20
Collection
MO.
21
12
DAY
23
24
YR.
25
26
Date
27
HO
21
UR
79
30
Other 1O
LOC.
31
M
32
33
SAMPLE
34
35
36
37
Event
38
39
40
41
42
Aliq.
m
; 44
45
46
Net Wt
mg
47
48
49
50
Counting Date
MO.
51
52
DAY
53
54
HOUR
5
56
57
58
LENGTH
59
60
61
Beta
Counts
62
63
64
65
66
67
B-BS
cpm
X
68
• X
69
70
Alpha
Counts
71
72
73
74
75
76
A-BG
cpm
•
77
X
78
X
79
80
-------