Appendix D Optimizing the CANBERRA iSERIES for Air Sample Counting
Figure 15 1 Hour PTFE Sample 10 Minutes After Collection
Users should be cognizant of the fact that different collection times will yield different
responses due to influences. Longer collection times tend to have a higher ratio of
thoron progeny to radon progeny until the point at which thoron equilibrium is
reached. Radon progeny equilibrium is reached much sooner so that increasing the
sampling time will not yield a higher uncompensated activity due radon. As a general
rule, radon equilibrium is reached in a few hours and thoron equilibrium is reached in a
few days.
Filter Media Selection
The iSERIES is designed to use all standard filter media types. Basic physics dictates
that some filter types work better than others. The primary criterion that improves the
compensation results is the microscopic smoothness of the filter media. The sample
collected on a glass fiber filter in Figure 16 was collected in the same location and
conditions as the PTFE filter collected in Figure 15. Notice how the compensated
results tend to register as positive much more often than shown with the PTFE sample.
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iMatic Automatic Counting System User's Manual - 9239221K
