Investigation of standard sources for determination of natural radioactivity

Comparative measurements are presented on standard ray volume sources used for the assay of natural radioactivity. The sources compared were made from Canadian and Russian uranium and thorium reference ores as well as from standardized solutions of 226Ra and 228Th. In addition, for 232Th chemically pure thorium compounds were used. Measurements were carried out with three types of detector, hyperpure Ge, Ge(Li) and NaI(Tl). The results of many comparative measurements in two different laboratories are discussed.