Appendix D Optimizing the CANBERRA iSERIES for Air Sample Counting
In reviewing a recent user's actual field results using a glass fiber filter, the algorithm
correctly compensated for 95%+ alpha interference and 90%+ beta interference.
Regions
Another way to improve the compensated results is to use the alpha region most
closely resembling nuclides expected to be found in any contaminated sample. There
are three compensated regions in the iSERIES:
Low - Uranium Region 3-5.0 MeV
Mid - Uranium, Americium, Plutonium Region 3-5.6 MeV
Std - Curium Region (3-6.4 MeV)
If uranium is the only element ever to be expected in the sample, the Low region should
be used. The difference in the results for the regions is shown in Table 4. The samples
are the same as discussed in Table 2 and Table 3.
Table 4 Comparison of Std and Low Regions
Alpha 3 - 6.4 MeV Alpha 3 - 5 MeV
Glass Fiber Model LB5211 A-O
170
100
PTFE
16
5
Glass Fiber Model LB5211 A-O
89
53
PTFE
4
2
The more restrictive the compensated region selection, the better the compensation
routine should work. Only use the region tat is necessary for best results.
Uncertainty of the Measurement
Like all measurements, the reported compensated activities have some uncertainty
associated with them. There are many factors that contribute to the uncertainty of a
given measurement. All other things being equal, the more compensation taking place
the higher the uncertainty as a percentage.
Table 6 shows some additional information on the samples displayed in Table 3. The
activity of a sample is reported as an amount, but the uncertainty should be considered
to report a range of values rather than simply a distinct result.
104
iMatic Automatic Counting System User's Manual - 9239221K
