Standardisation of low-activity actinide solutions by alpha-particle counting at a defined solid angle

In the frame of an IAEA co-ordinated research project 232U, 236Pu and 229Th tracers were standardised by alpha-particle counting at a defined solid angle. The aim of this project was to assign property values that are traceable to the International System of Units (SI). This article depicts the standardisation of the tracers, elaborating on problems related to low activity and interference from daughter nuclides. The activity concentrations of 232U, 236Pu and 229Th were found to be, respectively (734±4), (142.0±0.9) and (528.2±2.6) Bq g−1, at reference date (1 January 2003).