title: The standardisation of 229Th for an environmental yield tracer
abstract: The naturally occurring long-lived nuclides of thorium (228Th, 230Th and 232Th) are all alpha-emitters that are of interest both to the nuclear and non-nuclear industries and levels of these nuclides need to be monitored in both the working and natural environment. In order to do this in a manner where the results of radiochemical analysis are traceable to national standards, a chemical yield tracer has to be employed. 229Th has been identified as a suitable tracer for such purposes and has been used in the past. This paper describes the absolute standardisation of 225Th by 47pi alpha-gamma coincidence counting. The results of this work are presented together with an analysis of the standardisation uncertainties that were achieved in practice.
authors.affiliation: Centre for Ionising Radiation Metrology, National Physical Laboratory, Teddington, Middlesex, UK. piers.de.lavison@npl.co.uk
authors.lastname: de Lavison P
authors.initials: LJ
authors.lastname: Husband
authors.initials: SM
authors.lastname: Jerome
authors.initials: JD
authors.lastname: Keightley
authors.initials: AP
authors.lastname: Woodman
authors.initials: DH
authors.lastname: Woods
authors.initials: SA
authors.lastname: Woods