Stage 2 .Level 1, and for higher exposures: Check on significance of new measurement and consistency with previous evaluations
Level 1 refers to cases where it is expected that the dose from the intake is likely to be above 0.1 mSv. At this level the intake or dose from the measured values should be calculated explicitly. Before starting the assessment of intake and dose, however, it is recommended to plot the data and to do some simple hand calculations in order to understand the case (Step 2.0). In addition, the statistical significance of the measured value M should be estimated. This includes the assessment of uncertainty on M (Step 2.1) as well as the calculation of the contributions from previous intakes to M (Step 2.2) in order to decide whether M is:
due to a previous intake, or
Step 2.0: Understanding the case. Plot the data (including those from previous measurements if available) and do some simple hand calculations.
Step 2.1: Assessment of the uncertainty on M. Realistic estimates of the overall uncertainty on each data point are required. Here they are expressed as a total “scattering factor” (SF) (see how to assess uncertainty on data in Section 4.2.2).
Step 2.2: Calculation of the contributions P from previous intakes. The contributions (P) from all previous intakes of the radionuclide considered are calculated, taking into account all pathways of intake, and all intakes of mixtures where the radionuclide was involved.
Step 2.3: New intake confirmed. If M > SF2 * P, then there is a 95% probability for a new significant intake. Calculate the net value (N = M – P) of the radionuclide by subtracting P from the measured value M and go to Stage 3, in order to check whether the next stage of the task is Level 2 or Level 3
Step 2.4: New intake not confirmed. If P/SF2 < M < P*SF2, then the measured value M is consistent with the intakes assessed previously, and there is most probably no new intake (i.e., there is no evidence for a new intake). The evaluation stops and the measured value M is recorded together with all relevant information (radionuclide, activity, type of measurement, type of monitoring etc).
Step 2.5: Discrepancy with the previous evaluations. If M < P/SF, then there is a discrepancy with the previous assessments. The reason for the discrepancy could be (i) the measured value M is not reliable and/or (ii) the previous assessments are wrong. For example, an intake occurring near the end of the previous monitoring interval is likely to have been overestimated based on an assumed intake at the mid-point.
Step 2.6: Check on the reliability of M. For whole body counting possibilities for errors include: external contamination, mismatching of calibration and actual activity distribution (i.e. lung activity calculated with whole body efficiency, or lung activity calculated in the presence of residual GI tract activity etc.). For excretion measurements possibilities include contamination of the sample, incomplete collection of the sample, etc.).
Step 2.6.1: Reassess previous intakes. If it cannot be demonstrated that M is unreliable, then reassess the previous intake(s), i.e. go to the appropriate “Special procedure” at Stage 4.
Step 2.7: Check the measurement M. If it can be demonstrated that M is wrong, make corrections or repeat the measurement if possible and return to Step 2.0.