NBS TECHNICAL NOTE

U.S. DEPARTMENT OF COMMERCE/ National Bureau of Standards

I nterlaboratory I ntercom parisons

of Radioactivity Measurements

Using

National Bureau of Standards

. Mixed Radionuclide Test Solutions
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L 2 5 1975

^

Interlaboratory Intercomparisons of Radioactivity

' 8?5r Measurements Using National Bureau of Standards

Mixed Radionuclide Test Solutions

B. M. Coursey, J. R. Noyce and

J. M. R. Hutchinson

Institute for Basic Standards

U .S . National Bureau of Standards

Washington, D.C. 20234

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U.S. DEPARTMENT OF COMMERCE, Rogers C. B. Morton, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued August 1975
National Bureau of Standards Technical Note 875

Nat. Bur. Stand. (U.S.), Tech. Note 875, 20 pages (Aug. 1975) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1975

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.46:875). Price 65 cents. (Add 25 percent additional for other than U.S. mailing).
INTERLABORATORY INTERCOMPARISONS OF RADIOACTIVITY

MEASUREMENTS USING NATIONAL BUREAU OF STANDARDS

MIXED RADIONUCLIDE TEST SOLUTIONS

B. M. Coursey, J. R. Noyce and J.M. R. Hutchinson*

In 1973 the National Bureau of Standards (NBS) distributed three calibrated

test solutions to interested laboratories. Two of these solutions each

contained nine gamma-ray-emitting radionuclides that the participants

were asked to identify and quantify. The third solution contained ° y Sr and °0Sr-S>0Y, and participants were asked to perform a quantitative

radioactivity analysis of the mixture. The results reported by all

of the participating laboratories are given here. Most of the activity

values reported for the mixed gamma-ray-emitting solutions were within

±20 percent of the corresponding NBS values, but less than half of the

laboratories reported y Sr and ^°Sr-^^Y activity values both of which

were within ±20 percent of the NBS values.

Key words: Environment; intercalibration; intercomparison; radioactivity;

radionuclide; radiostrontium.

This report is divided into two main parts, the first describing the intercomparison

of the two gamma-ray-emitting test solutions, and the second describing the strontiumyttrium radioactivity test solution intercomparison. A final section summarizes the

findings of both intercomparisons.

I. Intercomparisons of Mixed Gamma-Ray-Emitting Test Solutions

Introduction

In 1972 the National Bureau of Standards (NBS) began distributing mixed radionuclide

gamma-ray emission-rate Standard Reference Materials •• ' (SRM's) . These standards have

proven quite useful for calibrating Ge(Li) detector systems used in the analysis of environmental radioactivity.

In January 1973 NBS distributed 60 mixed radionuclide test sources as unknowns through

the Standard Reference Material Program. The two objectives of this distribution were

(1) to provide the participants with an opportunity to test their measurement techniques

using an unknown sample containing nine radionuclides which give rise to 31 gamma-ray

lines, and (2) to allow NBS to evaluate the measurement capabilities of a cross section

of users of gamma-ray-emitting radioactivity standards. After reporting results to NBS,

the users were provided with an SRM certificate (Appendix I).

The fourteen laboratories listed in Table 1 reported results for a total of 19 sources.

1 Figures in brackets indicate the literature references at the end of the paper.

Radioactivity Section, Center for Radiation Research, National Bureau of Standards,

Washington, D. C. 20234
Table 1

List of Participants, Mixed Gamma-Ray Test Solution

1. Allied Chemical Company, Idaho Falls, ID

2. Armed Forces Radiobiology Research Institute, Bethesda, MD

3. Atlantic Richfield Hanford Company, Richland, WA

4. Duke Power Company, Charlotte, NC

5. General Electric Midwest Fuel Recovery Plant, Morris, IL

6. Industrial Bio-Test Laboratories, Inc., Northbrook, IL

7. Maine Yankee Atomic Power Company, Wiscasset, ME

8. Millstone Point Company, Waterford, CT

9. Oak Ridge Associated Universities, Training Division, Oak Ridge, TN

10. Ontario-Hydro, Pickering Operations, Pickering, Ontario, Canada

11. Rochester Gas and Electric Corporation, Rochester, NY

12. State of Florida, Division of Health, Orlando, FL

13. Teledyne Isotopes, Westwood, NJ

14. Westinghouse Advanced Reactors Division, Madison, PA

The order in which participants are listed in this table does not

correspond to the order in which results are listed in Tables 2 and 3.
Experimental Details

The sources consisted of chromium-51, manganese-54, cobalt-58, iron-59, cobalt-60,

zinc-65, cesium-134, cesium-137-barium-137m, and cerium-144-praseodymium-144 in a solution

of approximately 4 N HC1. The solution also contained approximately 15 ug of stable

cation carrier per gram of solution for each of the radionuclides listed above.

The solutions were distributed in flame-sealed borosilicate-glass bottles of standard

dimensions.^] The larger of the two sources, SRM-4252, was contained in a 450-ml

cylinder, which was fabricated from standard borosilicate-glass tubing (75-mm O.D.).

The bottom of the bottle was a 5-mm plate-glass disk. Forty such sources were prepared

within a mass range of 478.5 - 480.0. g.

The smaller of the two sources, SRM-4253, was a 50-ml cylindrical source, with an outer diameter of 38 mm and a bottom thickness of 3 mm. The forty small sources prepared

were within a mass range of 53.4 to 53.7 g. The mass of solution for each SRM-4253 was given on the certificate to the nearest 0.01 g.

The 450-ml source was designed to simulate reactor waste water. For a typical source

the "Ofo activity in January 1973 was 4.5 x 10 uCi/ml. For the 50-ml source, which

simulates reactor primary coolant, the °°Co activity was about 8.2 x lO

-

-* yCi/ml.

The solutions were counted by each participant in the standard-dimension bottles or, usually, transferred to a container of his choice. Two laboratories used Nal(Tl) detectors, while the others used Ge(Li) detectors. It might be noted that laboratory E had a NaI(Tl)-shielded, Ge(Li) detector system.

Results

A reporting form and questionnaire were provided with each source. In most instances,

the activities or activities per gram of solution were reported as of the measurement date.

The reported values for each radionuclide were divided by the NBS values, corrected for

decay, to obtain X/NBS. Values for these ratios are given in Tables 2 and 3 for SRM-4252

and SRM-4253, respectively. Note that the fourteen laboratories were assigned code

letters from A to N. Single and double letters are used to denote 450- and 50-ml sources, respectively.

The results for the individual radionuclides are also shown in Figures 1-3. Each

laboratory reported separately random errors at the 99 percent confidence level and

estimated upper limits for systematic errors. We have used the linear sum of their

reported random and systematic errors in calculating their uncertainty for the ratio X/NBS.

Their uncertainties are represented as error bars on the plotted points in Figures 1-3.

Discussion

Two of the laboratories, I and L, used Nal(Tl) detector systems. Their results are

of particular interest because of the large number of laboratories which still use such

systems for environmental analyses. In Tables 2 and 3 it can be seen that both laboratories failed to identify 51 Cr, 58 Co, 65 Zn, 134 Cs, and 14 ^Ce in the mixture. The

reported value for ^Mn by laboratory L may include contributions from the Co photopeak

at 810 keV and the 134Cs photopeaks at 796 and 802 keV.

Of the other 12 laboratories, all of which used Ge(Li) detectors, laboratory A

evidently had a calibration problem at the time of this test. For the large source their

values were systematically about 25% higher than the NBS values, while for the 50-ml source (AA) they reported only one-half of the NBS value. Their reported values for

-^Cr were high for both sources.
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As is evident from Figures 1-3, the results reported by most laboratories are fairly

evenly distributed around the NBS value (i.e., X/NBS = 1). The shaded and unshaded blocks

on the histograms represent results for the 450- and 50-ml sources, respectively. The

laboratories appear to have measured the 50 ml and 450 ml sources about equally well.

In Figure 3 it can be seen, however, that most of the reported values for zinc-65 are

high. The zinc-65 photopeak at 1115.5 keV falls on the Compton edge of the cobalt-60

1333-keV gamma-ray. Therefore, for this mixture, errors in Compton background subtraction

may be relatively large.

II. Intercomparison of Strontium-89, Strontium-90-Yttrium-90 Radioactivity Test Solution

Introduction

90

Because of the long half life of Sr, and because it is a bone seeker, maximum

permissible radioactive concentrations of this nuclide in air and water 1 J are low compared

to those of most fission and activation products. The principal difficulties encountered

in radiostrontium analyses are (1) Sr and Y are pure beta-particle emitters, and

(2) y Sr, an essentially pure beta-particle emitter, is also often present in the samples.

Over the years, the Radioactivity Section of NBS has produced solution standards of

°"Sr and of y Sr- yuy f° r calibration of detectors and testing of radiochemical procedures.

In November 1973 the Section made available a test solution containing a mixture of these

standards in order to help environmental radioactivity monitoring laboratories evaluate

their radiostrontium analysis capabilities. Twenty-six organizations that included

Federal, State, industrial and educational institution laboratories purchased 30 ampoules,

and 15 purchasers returned results in a test report form. These laboratories were then

sent a Report of Calibration and a letter that stated the ratios of their activity values

to the NBS values as of the date of calibration. The participants are listed alphabetically in Table 4.

Experimental Details

89

The test solution was prepared by mixing calibrated solutions of Sr (SRM 4945-C)

and "0sr_90y (SRM 4919-C) . The initial activity of each radionuclide was chosen to simulate that often found in the primary coolant of water-cooled nuclear-power reactors. The

certified values for the radionuclide concentrations in the test solution and their

uncertainties are given in the Report of Calibration (Appendix II) along with impurity

and half-life information.

Each participant analyzed the test solution by the method (s) of his choice. In general, the methods used by any one laboratory were not necessarily the same as those

employed by other laboratories. However, the analytical methods used can be grouped

into three categories. These and the number of participants using each are as follows:

(a) Counting only the strontium activities after an initial separation

from "0y and precipitation with a strontium carrier, and recounting

after ingrowth of ^0y (4);

(b) Liquid-scintillation counting and Cerenkov radiation counting (2);

(c) Separation of strontium and yttrium activities, and counting each

after precipitations of strontium and yttrium carriers (9).

There were variations within each category, especially the last where several different

separation steps were utilized and several different precipitates were made.
Table 4

89 90 90 Participants in the Intercomparison of the Sr, Sr- Y Test Solution

The order in this table is different from that in Table 5.

1. Atomic Energy of Canada Limited, Commercial Products, Ottawa, Ontario.

2. Baltimore Gas and Electric Company, Calvert Cliffs Nuclear Power Plant, Lusby, MD.

3. E. I. DuPont de Nemours and Company, Savannah River Plant, Aiken, SC.

4. Emory University, Department of Physics, Atlanta, GA.

5. Florida Power and Light Company, Turkey Point Plant, Miami, FL.

6. General Electric Company, Vallecitos Nuclear Center, Pleasanton, CA.

7. Industrial Bio-Test Laboratories, Inc., Northbrook, IL.

8. Michigan Department of Public Health, Division of Radiological Health, Lansing, MI.

9. New York State Department of Health, Radiological Sciences Laboratory, Albany, NY.

10. Northern States Power Company, Monticello Nuclear Generating Plant, Monticello, MN.

11. NUS Corporation, Radiological Monitoring Programs, Rockville, MD.

12. State of Florida, Division of Health, Radiological Health Unit, Orlando, FL.

13. United States Atomic Energy Commission, Health Services laboratory, Idaho Falls, ID.

14. United States Environmental Protection Agency, National Environmental Research Center,

Las Vegas, NV.

15. United States Geological Survey, Denver Analytical Services Unit, Lakewood, CO.

10
The results of each participant were returned to NBS on a test report form that also

asked for information about the counting system and the radiochemical, counting and data

reduction procedures used in the analyses.

Results

The results reported by the 15 participants are given in Table 5 and Figure 4 as ratios of the participants' reported values of activity, corrected for decay to the date

of calibration, to the NBS calibrated activity value, for ° 7 Sr and for ' Sr plus ^ UY. These ratios are denoted as (X/NBS)gg and (X/NBS)g n respectively. Those laboratories

that used NBS radioactivity SRM's or radioactivity standards traceable to NBS to calibrate

their detectors have their code letters underlined. For each X/NBS ratio, Figure 4 shows

the random counting error at the 99 percent confidence level (inner bars), and the random

error plus the linear sum of the estimated upper limits of systematic errors (outer,

larger bars)

.

Discussion

The X/NBS activity ratios have a range from 0.251 to 1. 1.992 for 90 Sr plus 9 Y. The deviations of several of tl

89 c ,543 for u:7 Sr, and from 0.458

to 1.992 for ^ u Sr plus ?U

Y. The deviations of several of the ratios from unity are greater than the reported total uncertainties (Figure 4), and may be indicative of unsuspected systematic error in the analytical procedures of these laboratories. The distributions are not greatly skewed, the averages being 0.928 and 1.031, and the medians being

0.95 and 0.98 for (X/NBS) gn and (X/NBS)

qo respectively.

The agreement of the reported activity values with the calibrated values does not

appear to be strongly influenced by the analytical method used or when the analysis was

performed. Of the two results obtained by using an analytical method in category (b) one was in good agreement with the NBS value, the other was not. In general, activity

values for °°Sr acquired by an analytical method in category (c) were closer to the

NBS value than those obtained through methods in category (a). It should be pointed out,

however, that only four laboratories used an analytical method in category (a). Participants who performed their analyses within a few months after the date of calibration

tended to have results for ° 9 Sr that were more consistent with the NBS value than those

with later dates of analysis. There are no obvious reasons, however, for such correlations.

The seven participants who stated that they had used NBS radioactivity SRM's or other radioactivity standards that are traceable to NBS to calibrate their detectors,

reported, as a group, values in better agreement with NBS for ' u Sr- 90Y than those who

did not. Use of such standards apparently did not significantly help the participants

with their y Sr measurements.

The reported uncertainties varied greatly both in magnitude and in the relative

contributions of the estimated random and systematic errors to the total uncertainties.

It is clear, from Figure 4, that there is no obvious correlation between estimated

on errors and agreement with the NBS value. The uncertainties reported for the *Sr activity

values tended to increase as the time between the date of calibration and the date of

analysis increased, probably because of the decay of ""Sr.

Summary

A total of 14 laboratories, representing power reactors, industry, state health

organization and environmental consultant groups tested their measurement techniques on samples containing a mixture of nine gamma-ray- emit ting activation and fission products.

Seventy-nine percent and 85 percent of the reported results' for SRM 4252 and for SRM 4253,

respectively, fell within ±20 percent of the corresponding NBS values.

11
TABLE 5

Results of Interlaboratory Intercomparison of

89 90 90

Sr, Sr- Y Radioactivity Test Source

Laboratory F did not

89

report Sr

Laboratory- Date of (X/NBS)

89 (X/NBS)

9Q

Code Letter Analysis at date of NBS calibration

A 11-28-73 0.743 0.849

B 1-11-74 0.986 1.142

C 2-6-74 0.997 1.008

D 2-1-74 1.249 1.308

E 1-1-74 0.974 1.088

F 4-18-74 0.526

G 7-9-74 1.543 0.908

H 4-25-74 0.995 0.940

I 12-6-73 0.629 0.458

J 2-15-74 0.813 1.992

K 7-25-74 1.230 1.163

L 8-2-74 0.930 0.827

M 7-17-74 0.835 0.982

N 9-5-74 0.251 1.327

9-24-74 0.822 0.953

Average 0.928 1.031

Median 0.95 0.98

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jG o w — 4-1 _l .-1 < • B co > C O 4-1 O U Q •H M-| 4J 00 UJ

4-J D 4-j a) O H .-1 C Vj CU O <D CO o en u

CL

ai en

4-1 l(H U

10 1*4 CJ

01 -H JD o

Y

radioactivity

t

are,

in

general,

d

ly;

outer,

larger

<a- ON c

CM 1 T3 O

U C

CO (J 10 O ^4 z*-\ CTi -sT O m

UJ M S-J o z> •» 0) 5-4 o

CM _| 1-1 r-J 01 u

c/3 ,o u < ON CO E CD > 00 HOXI CJ CO 01 c c •H ^m x; -h co

4-1 1-1 4J

Ctl 2 XI e \

1-1 0) 0) O 4J l-l

0) u

Ul 4-1 CO CO ffl <M=>

•H

0) H CO en _• _l 4J M < i-l 0) CO X) > 3 U J3 0) en co 4-J Q CU !-i rt UJ U C V

O C H

x) en c 4-1 CD -H M en o 4J 1-1 • CD Q_ l-i co Ul O ft • Ul ft B C 3

01 o o ^H o 03 cj en ft

CD

)-3M

13
89, 90 90 Sr- U Seven of the 15 laboratories that participated in the ~'Sr, Y test solution

intercomparison reported pairs of activity values with both values within ±20 percent

of the NBS calibrated values; nine reported pairs with both values within ±25 percent.

Of all activity values reported, 62 percent were within ±20 percent of the NBS values.

It should be noted that the test solutions used in these intercomparisons contained

stabilizing carriers in acid media and no interfering chemical species. The accuracies

obtainable in routine analyses of radioactivity in environmental samples are not likely

to be better than the agreements of the reported values in this intercomparison with the

NBS values. The conclusions reached by Fukai e_t al . l-^-l in an intercomparison of fissionproduct activities in sea water also seem applicable to these two intercomparisons. They

noted that "only in a few cases was unsatisfactory performance related to the methods

used," and "generally, bad results seem to be related to the lack of 'good housekeeping,'

especially of stringent attention to calibration of counting equipment."

Acknowledgement

The authors gratefully acknowledge the assistance of Miss L. M. Cavallo in the

development of the prototype standards, and Miss P. A. Mullen in the preparation of the test sources. The authors also wish to express their appreciation to Dr. W. B. Mann for

many helpful discussions during the development of these standards.

References

1. Cavallo, L. M. , Coursey, B. M. , Garfinkel, S. B. , Hutchinson, J.M.R. , Mann, W. B.

,

"Needs for Radioactivity Standards and Measurements in Different Fields", Nucl. Instrum. Methods, 112, 5 (1973).

2. "Standards for Protection Against Radiation," Code of Federal Regulations, Title 10,

Ch. 1, Part 20.

3. Fukai, R. , Ballestra, S. and Murray, C. N. , Proc. IAEA Symp. , "Interaction of Radioactive Contaminants with Constituents of the Marine Environment," (Seattle, Washington,

1972), International Atomic Energy Agency, Vienna (1973).

14
U. S. Department of Commerce

Frederick B. Dent

Secretary

National Bureau of Standards

Richard W. Roberta, Director Appendix I

Rational ^Bureau of Standards

Certificate

Standard Reference Material 4252

Mixed Radionuclide Radioactivity Standard

This standard consists of chromium-51, manganese-54, cobalt-58, iron-59,

cobalt-60, zinc-65, cesium-134, cesium-137, and cerium-144 in grams

of approximately 4N HC1 in a flame-sealed borosilicate glass bottle of

standard dimensions. The solution also contains approximately 15 ppm by

weight of stable cation carrier for each of the radionuclides listed above.

This standard was made by weighing an aliquot of a calibrated radionuclide

mixture into the bottle containing the acid. This calibrated mixture was prepared by mixing standardized solutions of the individual radionuclides.

The cerium-144 was calibrated by gamma-ray intercomparison with material

which had previously oaten standardized by 4rrf?-Y coincidence counting. The

radioactivities of X~&e other standardized solutions used were determined

by means of the NBS calibrated 4Try-ionizat ion chamber.

The radioactivities of wfe~constltuents in nuclear transformations per second

at 1200 EST January 15, 1973, a*e shown in the table below.

Radionuclide

51

54.

58

5960

65 134

137 144

CrMn

CoFe

CoZn

CsCsCe

Uncertainty

Systematic

%

Total

4.3

2.6

3.0

2.7

1.4 2.7

2.6

2.1 3.0

* Assuming a gamma-ray intensity of 50.6 ± 0.4% for the 1.115-MeV

gamma ray. ** Assuming a gamma-i/ay intensity of 85.0 ± 0.37o for the 0.662_ MeV

gamma ray. The uncertainties in the radioactivities are the 99-percent- confidence limits

for the random error components, and the linear sums of the estimated upper

limits of conceivable systematic errors. This standard contains cobalt-57 as an impurity. The cobalt-57 activity was

less than 0.1 percent of the total activity on January 15, 1973. The gammaray energy spectrum of the standard was examined with a Ge (Li)-spectrometer

,

and no other impurity was observed.

This standard was prepared in the NBS Center for Radiation Research, Applied

Radiation Division, Radioactivity Section, W. B. Mann, Chief.

Washington, D.C. January 1973

20234 J. Paul Cali, Chief

Office of Standard Reference Materials

4252-1
formnbs-443 Appendix II

(REV. 11-65)

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

WASHINGTON, D.C. 20234

REPORT OF CALIBRATION

STRONTIUM-89, STR0fiTIUR-90-nTRIU^90

Radioactivity Test Solution

89 90 90 This source consists of Sr and Sr- Y in approximately 5 grams of

solution in a flame-sealed, borosilicate glass ampoule. The solution,

in 1 N HC1, contains, per gram, 0.01 mg of stable strontium and 0.011 mg

of stable yttrium as carriers.

89

The Sr activity in nuclear transformations per second per gram of

solution at 1200 EST on November 1, 1973, was

* 90.3, ± 3.5% * . 6

89 The Sr in this test solution came from NBS Standard Reference Material

4945-C that was calibrated by means of 4tt8 proportional counting.

89

The uncertainty in the Sr activity, 3.5 percent, is the linear sum

of 1.3 percent, which is the 99 percent confidence limit of the 4tt8 measurements (9.925 S , where S is the standard error, and 9.925 is

the Student t factor for three sets of measurements), and the estimated

upper limits of conceivable systematic errors.

90 90 The total combined activity of Sr and Y, in equilibrium, in nuclear

transformations per second per gram of solution at 1200 EST on November 1,

1973, was

* 5.13 ± 3% * . 90 90 The Sr - Y in this test solution came from NBS Standard Reference

Material 4919-C that was calibrated by means of 4tt3 proportional counting.

90 90 The uncertainty in the Sr- Y activity, 3 percent, is the linear sum

of 1.3 percent, which is the 99 percent confidence limit of the 4tt6 measurements (4.541 S , where S is the standard error, and 4.541 is

the Student t factor for five sets of measurements) , and the estimated

upper limits of conceivable systematic errors.
The Standard Reference Materials used in preparing this test solution

were examined with a Ge(Li) spectrometer system for gamma-ray-emitting

impurities, and the 89 Sr was found to contain 5°Co, °5zn an(j 85g r#

The activity ratios, 58Co/ 89 Sr, 65 Zn/89sr and 85 Sr/ 89Sr. had upper

limits of approximately 6 x lO"-*, 4 x 10"^, and 6 x 10" , respectively,

as of November 27, 1973.

A half life of 50.60 ± 0.12 days for the 89 Sr in this test solution

was derived from ten sets of 2Tr3-ionization-chamber measurements made

on each of two samples over a period of two months. The uncertainty,

0.25 days, is the 99% confidence limit. A half life of 28.5 ± 0.8

years for 90 Sr is suggested; this is the half life adopted by the com- pilers of the Nuclear Data Tables (Section A, Vol. 8, Nos. 1-2,

Oct., 1970).

For the Director,

W. B. Mann, Chief

Radioactivity Section

Center for Radiation Research
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR RHFORT NO. NBS TN-875

2. Gov't Accession

No.

3. Recipient's Accession Nc

4. TITLE AND SUBTITLE

Interlaboratory Intercomparisons of RadioactivityMeasurements Using National Bureau of Standards

Mixed Radionuclide Test Solutions

5. Publication Date August 1975

6. Performing Organization Code

7. AUTHOR(S)

B. M. Coursey, J. R. Noyce and J. M. R. Hutchinson

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit Nc

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address fStreer, City, State, ZIP)

Same as Item 9

13. Type of Report & Period CoveredFinal

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less (actual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

In 1973 the National Bureau of Standards (NBS) distributed three calibrated

test solutions to interested laboratories. Two of these solutions each

contained nine gamma- ray- emitting radionuclides that the participants

were asked to identify and quantify. The third solution contained °°Sr

and 90Sr-90y, and participants were asked to perform a quantitative

radioactivity analysis of the mixture. The results reported by all of the

participating laboratories are given here. Most of the activity values

reported for the mixed gamma- ray- emitting solutions were within ± ZO

percent of the corresponding NBS values, but less than half of the

laboratories reported 89sr and 90s r -90y activity values both of which

were within ± ZO percent of the NBS values.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Environment; intercalibration; intercomparison; radioactivity; radionuclide;

radio strontium

18. AVAILABILITY f^T Unlimited

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