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:
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". 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. 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.
The bjkl values are presented in Table 3. Table 4 lists the bjk 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 bjkl and bjk satisfied the performance criteria for relative bias.
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 sjk values indicate within-analyst repeatability, in addition to inter-laboratory precision.