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Fission/Activation Products Urinalysis Intercomparison October - 2006

Table of Contents

Results

Samples were distributed to nine laboratories. Nine laboratories submitted results for gamma spectrometry and four for gross beta screening. In this report, performance criteria will be applied only to results submitted for the measurement of Cs-137, Co-60 and Ba-133. The results submitted for these analyses are listed in Table 1. The equations used for evaluating bias and precision are given in Appendix A.

The graph and tables on the gross beta results are provided in Appendix B for information purposes only and were included primarily for the benefit of those participants who use this technique as a screening procedure.

The terms used in the equations and the attached tables and figures are defined as follows:

y_jkl

the result obtained by correcting the measurement for a spiked sample by the value obtained for the appropriate urine blank.

b_jkl

the relative bias of the result obtained for each aliquot of a particular spiked sample. It represents the difference between the measurement and the true value, normalized by the true value.

b_jk

the mean relative bias, i.e. the mean of the bjkl values for a particular spiked sample.

s_jk

relative precision, calculated as the standard deviation of the relative bias of measurements of aliquots of the same spiked sample.

MDA

Minimum detectable activity. This is an indication of the detection capability of a participant's analytical method.

MTL

Minimum testing level. The minimum amount of radioactive material at which a dosimetry service should be tested for it to be in compliance with the Canadian Nuclear Safety Commission (CNSC) license requirements for performance in an independent testing exercise.

The CNSC has set its performance criteria for bioassay measurements in Regulatory Standard S-106, "Technical and Quality Assurance Standards for Dosimetry Services in Canada"[2]. At levels equal to or greater than the MTL, the limits for acceptable bias and precision are:

-0.25 ≤ Mean relative bias ≤ +0.50

Relative precision ≤ 0.40

Note that the MTL is set at five or more times the MDA. The MDA values used for this intercomparison were based on values given in S-106 or cited in ICRP[3]. These values are:

I-131: 20 Bq/L (N.B. Ba-133 was used as surrogate)
Cs-137: 20 Bq/L
Co-60: 25 Bq/L

The known performance of Canadian bioassay laboratories was taken into consideration in setting these MDA values.

Relative Bias:

The y_jkl values and their means for the gamma spectrometry analytical results are in Table 2. The y_jkl values are also presented graphically in Figures 1, 2 and 3.

The b_jkl values are presented in Table 3. Table 4 lists the b_jk values which are also shown graphically in Figures 4, 5, and 6. With the exception of Laboratory 8 values for Ba-133 and Co-60, all values of b_jkl and b_jk satisfied the performance criteria for relative bias.

Relative Precision:

The s_jk values are presented in Table 5, and Figures 7, 8, and 9. All values were within theacceptable relative precision limit.

For the participants who followed the recommended protocol (all except Laboratory 2) of only one analyst performing measurements for all blank and spiked samples, the s_jkvalues indicate within-analyst repeatability, in addition to inter-laboratory precision.