Improved sample preparation procedure for gross alpha counting on gas-flow proportional counter

Sample residue uniformity is crucial for accurate gross alpha counting using a gas-flow proportional counter, however this can be difficult to achieve using conventional procedures. An evaporation method using a 1:1 mixture of deionized water and 2-propanol yielded uniform 230Th and 241Am nitrate salt residues on metal planchets for gross alpha counting. The gross alpha efficiency and alpha:beta crosstalk behavior were studied using the evaporation procedure and a separate barium sulfate/ferric hydroxide coprecipitation method. The gross alpha efficiency data were fitted with empirical power law functions. The alpha:beta crosstalk behavior was different for the two radionuclides studied.