Direct counting of soil wafers: An improved total alpha/beta screening analysis

Although potentially very useful as a screening tool, currently-applied “gross” alpha/beta analyses are often considered unreliable by the environmental monitoring community. We describe here an alternative approach based on direct counting of pressed soil “wafers” to estimate total alpha/beta activities. The system was calibrated using a series of natural soils and sediment standards with total α/β activities estimated by use of a combination of available certified values, equilibrium assumptions, and our own measurements. A set of 10 such standards that span a wide range of activities were prepared by thoroughly mixing several grams of selected NIST and IAEA natural matrix standards together with reagent grade cellulose in a 4∶1 sample-to-binder ratio and pressing in a 40-mm stainles steel die. The resulting wafers, assumed to be at infinite thickness for expected radionuclides, were counted in a gas flow proportional counter set for simultaneous α/β counting. Both the alpha and beta count rates increased in a linear, systematic manner with increasing total estimated activities. This technique should prove to be an inexpensive, simple, and waste-free approach for screening total radioactivity in soil samples.