metrologia, 49 tech. suppl. · 232th, 230th, 228th, 228ra, 137cs, 210pb, 90sr, and 40k) in biota...

Metrologia, 2012, 49 Tech. Suppl. 06014

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Activity measurements of a suite of radionuclides (241

Am, 239,240

Pu, 238

Pu, 238

U, 234

U, 235

U, 232

Th, 230

Th, 228

Th, 228

Ra, 137

Cs, 210

Pb, 90

Sr, and 40

K) in biota reference material (Ocean

Shellfish)

CCRI(II)-S3

S. Nour*, L. R. Karam§, K. G. W. Inn

§

*University of Maryland, USA; §NIST, USA

Abstract

In 2005, the CCRI decided that a comparison undertaken from 2002 to 2008 by the NIST

(under the auspices of the Inter-America Metrology System [SIM]) in the development of

a new biota (Ocean Shellfish) standard reference material (SRM) was sufficiently well

constructed that it could be converted into a supplementary comparison under CCRI(II),

with comparison identifier CCRI(II)-S3. This would enable the comparison to be used to

support calibration and measurement capability (CMC) claims for radionuclide

measurements in reference materials (specifically, animal-based organic materials).

Previous comparisons of radionuclides have been of single or multiple nuclides in non-

complex matrices and results of such could not be extended to support capabilities to

measure the same nuclides in reference materials. The results of this comparison have

been used to determine the certified reference value of the SRM. The key comparison

working group (KCWG) of the CCRI(II) has approved this approach as a mechanism to

link all the results to certified “reference values” in lieu of the key comparison reference

value (KCRV) of these specified radionuclides in this type of matrix (shellfish) so as to

support CMCs of similar materials submitted by the present participants.

1. Introduction

In the field of radionuclide metrology (radioactivity measurements), a particular issue had arisen

with regards to CMCs of reference materials (soils, organic matrices, natural waters, etc.), most

of which had not been subject to either key or supplementary comparisons. While the

measurement of their contributing radionuclides (such as 137

Cs) had been compared, and such

comparisons are used to support the CMCs of a given radionuclide even in a reference material,

the comparison of the reference materials themselves offers very specific and often recalcitrant

difficulties. In addition to the preponderance of a vast variety of reference materials, many of

which are considered by only one laboratory, how such material is to be handled (sampling) and

prepared for analysis (i.e., procedures used to extract the nuclides of interest from the matrix

quantitatively) present potential problems for any kind of comparison.

Biological organisms, including shellfish, are routinely used as indicators for the radionuclide

levels in the marine environment, which is important for environmental monitoring,

oceanography, biological uptake studies, and food composition. An international workshop of

oceanographers, regulators, and metrology laboratory representatives, held at NIST in 1994,

revealed that measurement reference materials needed for studies of radionuclides (including of

Cs, Sr, Pu, Am, and Pb) in oceans included ocean sediment, fish, shellfish, seaweed, and water to

meet the core needs of the oceanographic and monitoring communities. Ocean shellfish was

considered an optimal candidate for an ocean-matrix reference material because of its capacity

for accumulating radionuclides from seawater (bioaccumulating). As a bioaccumulator, shellfish

was already being used as an indicator of a variety of contaminations in ocean environments.


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The material was developed in cooperation with member laboratories of the International

Committee for Radionuclide Metrology (ICRM) and other experienced metrology laboratories,

and was developed to be used in tests of measurements of radioactivity contained in matrices

similar to the sample, for evaluating analytical methods, and as a generally available calibrated

“real” sample matrix for laboratory comparisons.

2. Participants

Four NMIs/designated institutions and two international organizations, and an additional six

laboratories, participated in a comparison of one or more of the nuclides in the Ocean Shellfish

reference material matrix, and provided results in the agreed-upon format. Laboratory details are

given in Table 1. The comparison was piloted by the NIST.

Table 1. Details of participants in the CCRI(II)-S3 supplementary comparison*

Institution Full name Country

Regional

metrology

organization

ANSTO Australian Nuclear Science and Technology

Organization Australia APMP

IAEA International Atomic Energy Agency Marine

Environmental Laboratory Monaco

---

INER Institute of Nuclear Energy Research Chinese Taipei APMP

IPSN lnstitut de Protection et de Surete Nucleaire France EURAMET

IRMM Institute for Reference Material and Measurements Belgium ---

JCAC Japan Chemical Analysis Center Japan APMP

NAREL National Air and Radiation Environmental Laboratory USA SIM

NIRS National Institute of Radiological Sciences Japan APMP

NIST National Institute of Standards and Technology USA SIM

STUK Research and Environmental Surveillance Finland EURAMET

TRMC Taiwan Radiation Monitoring Center Chinese Taipei APMP

Typhoon Scientific Production Association Typhoon Russia COOMET

* Bold indicates signatory to CIPM MRA

3. Material and methods used in comparison

3.1 Material

This Ocean Shellfish is a mixture of Irish Sea mussel (0.1 % w/w), White Sea mussel (12 %

w/w), and Japan Sea oyster (87.9 % w/w). The raw material was dried, blade milled, and

pulverized. The pulverized material was “V-cone” blended to optimize homogeneity, and

bottled in polyethylene bottles in 150 g aliquots. The final bottled material was sterilized with >

50 kGy of 60

Co radiation to satisfy export regulations and to increase shelf-life time.


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Table 2: Semi-quantitative composition (expressed as common oxides %) of ashed ocean

shellfish material based on X-ray fluorescence (XRF) analysis

Element Percent by mass (%) Element Percent by mass (%)

F <0.01 MnO 0.097

Na2O 19.7 Fe2O3 1.2

MgO 6.3 NiO 0.010

Al2O3 2.3 CuO 0.013

SiO2 8.2 ZnO 0.24

P2O5 31.5 Br 0.15

SO3 8.8 SrO 0.053

Cl 6.0 Y2O3 0.002

K2O 7.5 I 0.018

CaO 7.8 BaO 0.022

TiO2 0.11

Cr2O3 0.008 Total 100.01

When nonvolatile radionuclides were to be determined, participants were instructed to dry

samples of the material at 40 oC for 24 hours (cooled at room temperature in a desiccator) prior

to weighing. Laboratories were also advised to determine volatile radionuclides (e.g., 210

Po, 137

Cs, 210

Pb, 212

Pb and 214

Pb) on material as received (with separate samples dried as described to

obtain a correction factor for moisture); correction for moisture content was made to the data for

any volatile radionuclides before comparing with the values given by this report. This approach

limited the loss of these radionuclides during drying [1]. The mass lost on drying is typically

less than 4 percent.

Several (ten) bottles, each containing 150 g of prepared ocean shellfish material, were examined

for gamma-ray heterogeneity through measurement of emission rates by counting in a “5-in”

(12.7 cm) NaI(Tl) detector coupled to a multichannel analyser. The count rates from each

measurement were analysed for statistical differences at ten selected energy regions; no gamma-

ray heterogeneity was observed. Statistical tests for heterogeneity of transuranium radionuclides

were performed based on evaluation of 15 results (three replicates from 5 different bottles) by

alpha spectrometry analyses, which showed a between-bottle heterogeneity for the actinides.

Participants were advised that a within-bottle sample size of 30 g or larger be used for

radiochemical actinide analysis. Statements of uncertainty, tolerance limits, and ranges of

reported results incorporate the effects of heterogeneity.

3.2 Methods

Each laboratory was instructed to use either whole bottle or half-bottle samples for analysis, and

the radiochemical and detection methods of its choice. Participants were asked to provide data

for those nuclides (among 90

Sr, 137

Cs, 210

Pb, 226

Ra, 228

Ra, 237

Np, 234

U, 235

U, 238

U, 238

Pu, 239+240

Pu, 241

Pu,241

Am, 228

Th, 230

Th, and 232

Th) they are experienced in analysing; several laboratories also

analysed radionuclides not included in the original list. The various methods used are indicated

in Table 3. The NIST-calibrated tracer solutions (243

Am, 242

Pu, 232

U and 229

Th), to be used as

internal reference for both internal calibration and extraction efficiency determinations, were

provided by NIST. When in-house tracer solutions were used instead of the NIST-provided

tracers, they were to be cross-checked against the NIST tracer solutions.


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Table 3. Measurement methods of the participants of CCRI(II)-S3

Laboratory Radio-

nuclide Radiochemical Method(s) Detection Method(s)

IPSN, IRMM, STUK,

Typhoon 40

K

Non-destructive Germanium gamma-ray

spectrometry

JCAC, TRMC,

Typhoon 90

Sr

Total decomposition or acid leach

(any combination of the following

HNO3, HCl, HF, HClO4)

Beta-particle counting or Liquid

scintillation counting (total

decomposition only)

IPSN, IRMM, JCAC,

NIRS, TRMC,

STUK, Typhoon

137Cs

Non-destructive

Germanium gamma-ray

spectrometry

IPSN, IRMM, JCAC,

STUK 210

Pb

Non-destructive Germanium gamma-ray

spectrometry

IRMM, JCAC,

Typhoon 228

Ra Non-destructive Germanium gamma-ray

spectrometry

IAEA, INER, IRMM,

JCAC, NAREL,

NIRS, NIST, STUK,

TRMC

228Th




Silicon surface-barrier alpha-

particle spectrometry

IAEA, INER, JCAC,

NAREL, NIRS,

NIST, STUK, TRMC

230Th






ANSTO, IAEA,

INER, JCAC,

NAREL, NIRS,

NIST, STUK, TRMC

232Th





particle spectrometry or

inductively coupled plasma-

mass spectroscopy/atomic mass

spectroscopy

IAEA, INER, JCAC,

NAREL, NIRS,

NIST, STUK, TRMC

234U






IAEA, INER, JCAC,

NAREL, NIRS,

NIST, STUK, TRMC

235U






ANSTO, IAEA,

INER, IRMM, JCAC,

NAREL, NIRS,

NIST, STUK, TRMC

238U





particle spectrometry or

inductively coupled plasma-

mass spectroscopy/atomic mass

spectroscopy

IAEA, INER, IPSN,

JCAC, NIRS, NIST,

TRMC

238Pu






IAEA, INER, IPSN,

JCAC, NAREL,

NIRS, NIST, STUK,

TRMC

239+240Pu

Total decomposition, or acid

leach (any combination of the

following HNO3, HCl, HF,

HClO4)



IAEA, INER, IPSN,

IRMM, NIST, TRMC 241

Am

Non-destructive, total

decomposition, or acid leach (any

combination of the following


Germanium gamma-ray

spectrometry (non-destructive)

or silicon surface-barrier alpha-


(destructive methods)

No laboratory reported results for 237

Np, and there was insufficient data received for 226

Ra to be able to

derive a reference value.


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4. Results

Due to the complex nature of the material compared, and the variability in sample preparation

and analysis among the participating laboratories, the comparison reference values (RVs) are

taken as reference values for each radionuclide individually as long as at least one CIPM MRA

signatory’s results were included. In other words, the RVs are radionuclide-specific. The

determination of the RV of each radionuclide in the Ocean Shellfish material was accomplished

by using the radioanalytical results from each laboratory that measured the specific radionuclide.

Twelve laboratories world-wide participated in this comparison and reported their final results to

NIST, including the six CIPM MRA signatories identified in Table 1. For each laboratory result,

the mean value from replicate measurements was calculated together with its expanded

uncertainty (k = 2), which are shown in Table 4. One laboratory did not report uncertainties for

their mean values and, in this case, uncertainties were calculated by NIST as a standard deviation

from the reported results (2 sigma).

Table 4. Measurement results of radionuclides in Ocean Shellfish from participating

CIPM MRA Signatories (note: No CIPM MRA Signatory laboratory reported a 90

Sr

measurement). †

NMI Nuclide

Reported Value1

Massic Activity

mBq g–1

Expanded Uncertainty (k = 2)

mBq g–1

ANSTO

232Th 0.730 0.071

238U

1.535 0.418

IAEA, Monaco

228Th 1.99 0.06

230Th 0.48 0.02

232Th 0.70 0.02

234U 1.77 0.06

235U 0.072 0.008

238U 1.58 0.06

238Pu 0.010 0.001

239+240Pu 0.061 0.003

241Am 0.101 0.006

INER*

234U 1.542 0.448

235U 0.048 0.010

238U 1.314 0.343

IRMM

40K

171 8

137Cs

0.27 0.04

210Pb 6.6 1.0

228Ra

1.33 0.08

228Th

1.4 0.2

238U

1.6 0.4

241Am

0.12 0.04


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NMI Nuclide

Reported Value1

Massic Activity

mBq g–1

Expanded Uncertainty (k = 2)

mBq g–1

NIST

228Th 1.126 0.224

230Th 0.456 0.056

232Th 0.641 0.048

234U 1.570 0.122

235U 0.063 0.006

238U 1.514 0.064

238Pu 0.0096 0.0018

239+240Pu 0.053 0.002

241Am 0.099 0.011

STUK

40K 153 18

137Cs

0.28 0.10

210Pb 5.5 1.8

228Th 1.18 0.24

230Th 0.36 0.16

232Th 0.59 0.24

234U 1.53 0.40

235U 0.05 0.02

238U 1.31 0.46

239+240Pu

0.06 0.02

*Laboratory did not report expanded uncertainty for the mean. It was calculated by NIST as a standard

deviation from the reported results, 2 sigma. 1 Recommended sample size of at least 30 g for radiochemical analysis.

4.1 Calculation of the Massic Activity Value: the Reference Value

Results for the radionuclides analysed in this comparison are given in Table 5 and Appendix 1.

The massic activity, or RV (reference value), for each nuclide (Table 5) was determined from the

evaluated median of the individual laboratory means. The median was chosen due to its superior

robust statistical properties, especially in light of the observed statistically significant differences

between laboratories, which in turn were due to the variety of measurement and sample

conditions within the participating laboratories.

Table 5. Massic Activity Reference Values for CCRI(II)-S3. Reference date 16 February

1998

Radionuclide Half-life Used* Median ± U (k = 2)

[mBq/g]

95/95 Tolerance

Limits (mBq/g) 40

K

(1.2504 ± 0.0030) 109 a 160 ± 16 75 to 241

137Cs

(22.23 ± 0.12) a 0.25 ± 0.03 0.09 to 0.43

210Pb

(30.05 ± 0.08) a 6.9 ± 1.0 1.18 to 12.2

228Ra** (5.75 ± 0.04) a 1.33 ± 0.34 -1.08 to 3.56

228Th

(698.60 ± 0.23) d 1.35 ± 0.33 0.32 to 2.47

230Th

(7.538 ± 0.030) 10

4 a 0.41 ± 0.09 0.26 to 0.58

232Th

(1.402 ± 0.006) 10

10 a 0.64 ± 0.13 0.44 to 0.85

234U

(2.455 ± 0.006) 10

5 a 1.56 ± 0.16 1.27 to 1.92


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Radionuclide Half-life Used* Median ± U (k = 2)

[mBq/g]

95/95 Tolerance

Limits (mBq/g) 235

U

(7.04 ± 0.01) 108 a 0.061 ± 0.017 0.014 to 0.107

238U

(4.468 ± 0.005) 10

9 a 1.46 ± 0.15 1.06 to 1.83

238Pu (87.7 ± 0.1) a 0.009 ± 0.003 0.006 to 0.013

239+240Pu

(24100 ± 11) a

(6561 ± 7) a 0.055 ± 0.008 0.031 to 0.082

241Am

(432.6 ± 0.6) a 0.101 ± 0.016 0.059 to 0.151

*Half lives taken from Evaluated Nuclear Structure Data File (ENSDF), November 2006. The stated uncertainty is

the combined standard uncertainty

**Radium -228 activity values are based on measurements of its 228

Ac daughter

In addition to the RVs and their respective uncertainty values, Table 5 also provides the 95/95

(normal) tolerance limits. This normal tolerance method is based on the observation that the

individual laboratory means appear to be normally distributed about the RV. Whereas the RV is

an estimate of the middle of the population of laboratory means, and the expanded uncertainty

for the RV is at the 95 percent confidence limit, the tolerance limits are a measure of the spread

of the population of means as a whole across the specific measurand. A 95/95 tolerance limit

means that there is a 95 % confidence that 95 % of the population of laboratories mean values

fall within the specified limits. In Appendix 1, the solid line represents the RV for that

radionuclide, and dashed lines are the associated uncertainty for the median (k = 2).

4.2 Calculation of the Uncertainty of the Reference Values

In addition to a brief description of sample digestion and chemical separation methods used in

radiochemical analysis, chemical yield and determination methods used, sample geometry and

counting system used, sample identification (including dry sample weight and ratio of dry

sample to ash weight), and massic activity at the reference time, participants were asked to

provide an expanded uncertainty (at k = 2). Although all laboratories, save one, provided

uncertainties on their values, not all reported complete uncertainty budgets for all radionuclides.

Since this comparison was made with the objective of reference material certification, and the

reference values were to be based on calculations of central laboratory values, uncertainty

budgets were not requested from the participants. However, for this comparison, an example

uncertainty budget (from the NIST) is shown in Table 6.

Table 6. Uncertainty components for Ocean Shellfish analyses. Relative uncertainty of

output quantities (%) for an individual analysis.

Radio-

nuclide

Calibra-

tion

Sample

Prep

Radio-

chem.

Source

Prep

Coun-

ting

Spectrum

Analysis

Mass Tracer* Blank

228Th

0.1 0.2 0.5 0.2 1 5 0.1 0.3 0.5 230

Th 0.1 0.2 0.5 0.2 1 5 0.1 0.3 0.5

232Th

0.1 0.2 0.5 0.2 1 5 0.1 0.3 0.5 234

U 0.1 0.2 0.5 0.2 1 3 0.1 0.3 0.5

235U

0.1 0.2 0.5 0.2 4 3 0.1 0.3 0.5 238

U 0.1 0.2 0.5 0.2 1 3 0.1 0.3 0.5

238Pu 0.1 0.5 0.5 0.2 1 2 0.1 0.4 0.5

239+240Pu

0.1 0.5 0.5 0.2 1 2 0.1 0.4 0.5 241

Am 0.1 0.5 0.5 0.4 1 6 0.1 0.7 0.5

*An uncertainty component arising from the tracer is relevant for a single analysis, but not for the mean of several

measurements as the same tracer is used.


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Contributions to the uncertainty for measurements of these types of material include: instrument

calibration, weighing (gravimetric), sample dryness, nuclear data (half life, energy), tracer

measurement uncertainties (negligible), chemical yields, and counting statistics. Of all the

potential contributions to the uncertainty, only counting statistics and spectrum analysis methods

are considered to be significant for these types of actinide measurements in reference materials.

The combined standard uncertainties (uc) for each of the reference values (Table 5) were

computed by incorporating components from four sources: 1) the “bootstrapped” estimated

uncertainty of the median of the laboratory mean values as described below, 2) the k = 1

uncertainty associated with the radiochemical tracer SRMs (when used), 3) the uncertainty

related to bottle-to-bottle variation (heterogeneity), and 4) the uncertainty related to within-bottle

variation (heterogeneity). The within and between bottle heterogeneity of transuranics in the

material were estimated based on replicate results from one laboratory, and were incorporated

into the expanded combined uncertainties. The uncertainty components were combined in

quadrature as specified by the GUM [2] and NIST Guidelines [3]. The uncertainty components

of each individual reference value (radionuclide) in this comparison are given in Table 7.

Table 7. Uncertainty components for CCRI(II)-S3 Reference Values

Radio-

nuclide

Relative uncertainty of output quantities (at 2 sigma) in

%

Relative expanded

uncertainty (k = 2)

Bootstrap w/in bottle

heter.

Between

bottle heter.

Tracer % mBq/g

40K

10.0 not detected not detected § 10.0 16.0 137

Cs 13.0 not detected not detected § 13.0 0.033 210

Pb 14.5 not detected not detected § 14.5 1.03 228

Ra 25.6 not detected not detected § 25.6 0.342 228

Th 16.5 8.1 16.6 0.6 24.4 0.334

230Th

8.9 12.3 14.2 0.6 22.0 0.086 232

Th 7.5 14.3 13.0 0.6 20.3 0.133

234U

4.5 4.5 7.8 0.6 10.3 0.157 235

U 19.7 15.8 10.3 0.6 27.9 0.017

238U

8.7 3.1 4.4 0.6 10.3 0.149 238

Pu 8.9 17.8 21.5 1.2 33.3 0.003 239+240

Pu 12.7 4.2 3.6 1.2 14.5 0.008

241Am

10.5 7.0 9.8 1.4 15.8 0.016 § Participants used in-house tracers, the uncertainties of which are contained wholly within the uncertainty of the

median

A general closed-form formula approach does not exist for calculation of the uncertainty for a

median. To circumvent this problem, the "bootstrap" statistical method was utilized. The

bootstrap method is a general, computationally-intensive procedure for estimating and

computing the uncertainty of a statistic whose form is complicated and/or whose underlying

assumptions are non-standard. The virtue of the procedure is that it provides a straightforward,

rigorous methodology for computing uncertainties that would have otherwise been difficult or

impossible to obtain. For general bootstrap information, see reference [4]. The median, A , was

determined through a bootstrap estimate obtained as follows:


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1. From the original sample of n observations (that is, the n laboratory means), compute the

statistic of interest (e.g., the median of the means).

2. Compute a bootstrap sample that is a random sample (with replacement) from the original n

points. The bootstrap sample is constructed to also be of size n. The bootstrap sample will be

similar to – but not identical to – the original sample of n laboratory means.

3. Compute the statistic of interest (e.g., the median) from this bootstrap sample (this will be the

bootstrap statistic).

4. Repeat steps 2 and 3 a large number of times (e.g., 1000 times); the bootstrap statistic will, of

course, change from one bootstrap sample to the next.

5. Compute the standard deviation of the statistic by applying the usual standard deviation

formula to the 1000 bootstrap statistics.

Each laboratory (with one exception, which provided the result of a single measurement)

reported the mean of replicate measurements and the associated propagated uncertainty (or

standard deviation) at 2 sigma. As stated in section 4.1, the data set of laboratory means was not

normally distributed and, in such a case, the median is the most robust method of deriving

reference values. The uncertainty on an individual mean is encompassed wholly in the bootstrap

calculation of the uncertainty of the median of laboratory means, and is not treated separately.

4.3 Degrees of equivalence

In general, the degree of equivalence of a given measurement is the degree to which it is

consistent with the comparison reference value [5], and is indicated for each radionuclide and for

each NMI in Appendix 2. The degree of equivalence of a particular NMI, i, with the reference

value (RV) of a specific radionuclide in this matrix is expressed as the difference (Di) between

the NMI’s result, Ai, and the RV:

Di = Ai – RV (4)

together with the associated expanded uncertainty (k = 2) of Di, Ui, being given by the

expression:

Ui = 2uDi (5)

where uDi is the square root of the quadratic sum of all measurement uncertainty components [6]

for both the NMI’s result and for the RV. Although there is some degree of correlation between

the uncertainty of the NMI result and that of the RV result, the nature of deriving the reference

value as a median of NMI results minimizes the impact of this correlation and renders it as not

significant.

5. Results of comparison

Results for the radionuclides analysed in this comparison are given in Table 5 and Appendix 1.

For each radionuclide, the mean value is calculated for each laboratory together with an

expanded uncertainty (k = 2). In Appendix 1, the solid line represents the median (i.e., the

reference value) for that radionuclide and dotted lines are the associated uncertainty for the


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median (k = 2). All reported values were considered in the determination of the reference value

(no results were considered as outliers). The interest in the user community is exhibited by a

high rate of participation by non-NMIs in the comparison. Nevertheless, the high participation

also by CIPM MRA signatories [ANSTO, IAEA, INER, IRMM, NIST (the pilot laboratory), and

STUK] allows for several degrees of equivalence between individual labs and the comparison

reference value to be presented (Appendix 2). With a single exception (the IAEA’s result for 228

Th), the difference between a laboratory result and the reference value for a given radionuclide

(i.e., Di) was within the associated expanded uncertainty (k = 2), Ui.

6. Conclusions

A supplementary comparison, with comparison identifier CCRI(II)-S3, was undertaken by six

NMIs that analysed a suite of radionuclides in material derived from Ocean Shellfish in the USA,

NIST SRM-4358. Radionuclides included in this comparison were 40

K, 137

Cs, 210

Pb, 228

Ra, 228

Th, 230

Th, 232

Th, 234

U, 235

U, 238

U, 238

Pu, 239+240

Pu, and 241

Am. Some laboratories reported results for

additional radionuclides; however, since certified reference values currently exist for only the

listed radionuclides, these others are not included in these comparison results.

7. References

1 R. Bock, A Handbook of Decomposition Methods in Analytical Chemistry, International

Textbook Company, Limited. T. & A. Constable Ltd., Great Britain, 1979.

2 International Organization for Standardization (ISO), Guide to the Expression of

Uncertainty in Measurement, 1993. Available from the American National Standards

Institute, 11 West 42nd

street, New York, NY 10036, USA. 1-212-642-4900. (Listed

under ISO miscellaneous publications as “ISO Guide to the Expression 1993”).

3 Taylor, B.N. and Kuyatt, C.E., Guidelines for Evaluating and Expressing the Uncertainty

of NIST Measurement Results, NIST Technical Note 1297, 1994. Available from the

Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402,

USA.

4 Efron, B. and Tibshirani, R.J. (1993). An Introduction to the Bootstrap. Monographs on

Statistics & Applied Probability 57, Chapman and Hall, New York.

5 CIPM MRA: Mutual recognition of national measurement standards and of calibration

and measurement certificates issued by national metrology institutes, International

Committee for Weights and Measures, 1999, 45 pp. http://www.bipm.org/pdf/mra.pdf.

6 Ratel, G., Evaluation of the uncertainty of the degree of equivalence, 2005, Metrologia

42, 140-144.

http://www.bipm.org/pdf/mra.pdf

http://iopscience.iop.org/0026-1394/42/2/009/

http://iopscience.iop.org/0026-1394/42/2/009/


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Appendix 1. Comparison results of each nuclide


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Appendix 2. Comparison results for each CIPM MRA signatory participant

Lab, i

↓

40K

137Cs

210Pb

228Ra

228Th

230Th

Di Ui

mBq/g

Di Ui

mBq/g

Di Ui

mBq/g

Di Ui

mBq/g

Di Ui

mBq/g

Di Ui

mBq/g

ANSTO

IAEA 0.64 0.34 0.07 0.11

INER

IRMM 11 18 0.02 0.05 -0.3 1.4 0.00 0.35 0.04 0.39

NIST -0.22 0.56 0.05 0.14

STUK -7 24 0.03 0.10 -1.4 2.1 -0.17 0.41 -0.05 0.18

Lab, i

↓

232Th

234U

235U

238U

238Pu

239+240Pu

241Am

Di Ui

mBq/g

Di Ui

mBq/g

Di Ui

mBq/g

Di Ui

mBq/g

Di Ui

mBq/g

Di Ui

mBq/g

Di Ui

mBq/g

ANSTO 0.09 0.19 0.08 0.17

IAEA 0.06 0.18 0.21 0.29 0.011 0.025 0.11 0.18 0.001 0.006 0.001 0.016 0.001 0.033

INER -0.02 0.91 -0.012 0.029 -0.15 0.37

IRMM 0.14 0.43 0.020 0.045

NIST 0.00 0.16 0.01 0.29 0.003 0.024 0.05 0.20 0.000 0.003 -0.007 0.010 -0.001 0.023

STUK -0.05 0.27 -0.04 0.43 -0.010 0.028 -0.15 0.48 0.000 0.014