Americium-241 for alpha-irradiations

Abstract

The motivation for the present investigation was provided by the practical difficulties encountered in using a Cm-242 source for alpha-irradiation in fine-grain dating. These are: (a) short half- life (163d), (b) subsequent build up of Pu-238, which has a lower alpha-energy (5.5 MeV instead of 6.1 MeV), (c) source only available with a discreet and fragile window and (d) increasing difficulties in its commercial availability. It was therefore imperative to reconsider the available alpha sources, with the objective of finding a viable alternative. The obvious criterion for a suitable alpha-source is that it has a high alpha-energy, a long half-life and that, it does not give a significant dose rate from any other decay mode. We shall first outline the difficulties (and possible complications) arising from the use of a Cm-242 source and then describe a feasibility study on the use of Am-241 (type AMM3, commercially available from R.C.C., Amersham, Bucks. England HP7 9LL). This is a robust rolled strip in which Am-241 is incorporated in a gold matrix (~ 1 mum thick,) backed with silver. The active surface has a protective coating of a gold-palladium alloy (~ 2 mum thick).