Alpha / Beta ABA - 005 High Throughput Screening of Samples Containing Alpha & Beta Radionuclides : an Overview of Methods by Jim

The growing need to quantitate alpha emitting radionuclides in the environment and in nuclear fuel processing and disposal has resulted in dramatic increases in gross alpha/gross beta measurements. In fact, gross alpha/gross beta counting has become the most widely used method of monitoring for the presence of radioactivity. Much of the interest is due to the need to address safety, regulatory compliance, and disposal issues for both alpha and beta radionuclides. The potential for litigation has also heightened interest in screening samples for gross alpha/ gross beta activities. Traditionally, gas flow proportional counting has been used for making gross alpha/gross beta measurements. However, gas flow proportional counting has some disadvantages when compared to liquid scintillation counting (LSC). Counting efficiencies for alphas are 30%, or less, compared to nearly 100% for LSC. Alpha particles, and to a lesser extent beta particles, are attenuated by salts and solids dried onto a planchet. In fact, 100 mg of solids will reduce the absolute alpha counting efficiency from 30% to 10%. Attenuation is not a problem with the LSC method because the sample is completely dissolved in the counting cocktail. No energy resolution is possible with gas flow systems. There is also no way to detect tritiated water with gas flow methods since the sample must be evaporated to dryness, thus volatilizing the tritium.