Examination of Low-Sodium Salts for Radiation Education

Various materials containing the natural radioisotope potassium-40 ( 40 K) are often used for radiation education, but their radioactivity is not usually known. In the present study, low-sodium salts (LS salts) were purchased at several shopping malls in Japan, and the radioactivity of 40 K in the LS salts were calculated from the nutritional tables and cutting down rates (CDR) printed on their packages. CDR is the percentage of sodium chloride (NaCl) in common salts replaced with potassium chloride (KCl). Solid disks were fabricated from the LS salts and KCl reagent, and their radiation count rates (cps/g) were measured by GM survey meter and CsI spectrometer. In these measurements, the KCl disk was used to determine the conversion factors (Bq/cps) for determining radioactivity of 40 K in the LS salts. It was found that the experimentally obtained radioactivity generally coincides with that calculated from the nutritional tables, but it does not always coincide with that calculated from CDR.