Prompt retrospective air sample analysis--a comparison of gross-alpha, beta-to-alpha ratio, and alpha spectroscopy techniques.

The long-standing problem related to prompt analyses in continuous air sampling or monitoring has been the well-known interference of the radon- and thoron-progeny co-deposited on the filtration media with any potential suspect radionuclides. The solutions to this problem have been quite diverse, and have included, for example, simple gross-alpha screening, the use of beta-to-alpha ratios, and/or the use of alpha spectral analyses. In the context of week-long retrospective continuous air sampling, this paper will explain, in detail, the technical basis for the use of the simple gross-alpha screening, beta-to-alpha ratio, and alpha spectrometry techniques and demonstrate the efficacy (or lack thereof) of these methods with simple examples. Although the most sensitive analysis technique for week-long retrospective continuous air samples is no doubt a long-lived count performed typically after at least a four-day decay period, when necessary, certain prompt and semi-prompt techniques discussed here can approach a sensitivity that is within about an order of magnitude of the long-lived count.