The assay of 228Ra in biological material

Some aspects of possible interference in the assay of 228Ra in biological samples were investigated. 228Ra is determined, after coprecipitation with BaSO4, by counting its daughter 228Ac carried on LaF3, due corrections being made for Ba and La recoveries. Tracer studies with 133Ba, 45Ca, 89Sr, 91Y and 234Th, under assay conditions, showed that (i) the small amount (5 mg) of Ba carrier is recovered nearly quantitatively after complete separation from large amounts of Ca (30-480 mg) which if precipitated with Ba would distort the results by falsely high Ba recoveries, (ii) fall-out Sr and Y, as well as natural Th, would not interfere in the assay and (iii) LaF3, in the amounts involved in the assay, produces negligible self-absorption but would enhance the 228Ac activity by as much as about 18% due to scattering.