The following report summarizes the results obtained in the June 2006 sample distribution for the Tritium/Carbon-14 Intercomparison Program, which is administered by the National Calibration Reference Centre for Bioassay, Radiation Protection Bureau.
Samples were prepared as described in previous reports [1,2] and were spiked with both tritium and carbon-14. The spike levels tested were:
Tritium: 2.52 x 104 Bq/L
Carbon-14: 3.34 x 103 Bq/L
and the date of spiking was May 11, 2006.
Each participant was provided with five aliquots of the dual spiked sample and of the urine blank from which the spiked sample had been prepared. Instructions for sample analysis and reporting of results were enclosed with the samples.
Samples were distributed to eleven laboratories. Nine returned results as requested. These results are presented in Table 1.
The equations used to evaluate the bias and precision of results are given in the appendix. The terms used in the equations and the attached tables and figures are defined as follows:
The Canadian Nuclear Safety Commission (CNSC), formerly the Atomic Energy Control Board, 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. In S-106, the MDA for urinalysis has been set at 70 Bq/L for carbon-14 and at 400 Bq/L for tritium. The known performance of Canadian bioassay laboratories has been taken into consideration in setting these specifications .
The yjkl values and their means are listed in Table 2 in the same format and with the same number of significant figures given in the reports submitted to the Bureau. The yjkl values are also presented graphically in Figures 1 and 2.
The bjkl values are presented in Table 3. Values that exceeded the acceptable relative bias limits are marked with an asterisk in the table.
Table 4 lists the bjk values which are also shown in Figures 3 and 4. All values satisfied the performance criteria for mean relative bias.
The sjk values are presented in Table 5 and Figures 5 and 6. All values were within the acceptable limit for relative precision.
For the participants that followed the recommended protocol (all except Laboratory 7 in this intercomparison) of only one analyst performing measurements for all the blank and spiked samples, the sjk values indicate day-to-day within-analyst variability in addition to intra-laboratory precision.
Nine laboratories participated in this intercomparison. The number of participants that obtained mean relative bias and relative precision values of 5% or less are as follows:
|Mean Relative Bias||Relative Precision|
|Tritium:||2.52 x 104||7||7|
|Carbon-14:||3.34 x 103||7||6|