Determination of radium-228 in foods and water.

A procedure was developed for the rapid determination of 228Ra by measuring its decay product 228Ac. The method is applicable to a variety of types of samples such as food and water. Food samples can be prepared by dry- or wet-ashing techniques. The 228Ac is precipitated with lanthanum carrier, dissolved, purified by solvent extraction, and finally decontaminated on anion and cation exchange resins. The 228Ac is counted in a thin-window, low-level gas flow beta counter. It may be necessary to count the sample several times to follow the 6 h half-life of 228Ac so that its purity is ensured. The method is sensitive to 1 pCi/sample of food ash and to 1 pCi/L of water.