Determination of 227Ac by α-particle spectrometry

A method is described for the determination of 227Ac concentrations in environmental samples. Actinium is separated from the sample digest by co-precipitation with lead sulphate, purified using anion and cation exchange techniques, and electrodeposited onto a stainless-steel disc. The chemical yield is monitored by addition of a 229Th/225Ra/225Ac tracer before sample dissolution. 225Ac recovery is determined from an initial count by measurement of its α-emitting daughter, 217At. The disc is then stored for 2–3 months and recounted. The 227Ac activity is obtained by measurement of the ingrown 227Th and 223Ra activities in the 5.38–6.10 MeV region. Co-precipitation with lead sulphate enables the convenient determination of actinium, thorium and radium on the same sample digest.