Evidence for age-related performance degradation of ²⁴¹Am foil sources commonly used in UK schools

Abstract

The characteristics of alpha radiation have for decades been demonstrated in UK schools using small sealed (241)Am sources. There is a small but steady number of schools who report a considerable reduction in the alpha count rate detected by an end-window GM detector compared with when the source was new. This cannot be explained by incorrect apparatus or set-up, foil surface contamination, or degradation of the GM detector. The University of Liverpool and CLEAPSS collaborated to research the cause of this performance degradation. The aim was to find what was causing the performance degradation and the ramifications for both the useful and safe service life of the sources. The research shows that these foil sources have greater energy straggling with a corresponding reduction in spectral peak energy. A likely cause for this increase in straggling is a significant diffusion of the metals over time. There was no evidence to suggest the foils have become unsafe, but precautionary checks should be made on old sources.

Surface degradation of laminated metal 226Ra foils used in school sealed sources in the UK

“…The cup-style sources currently sold by UK science equipment suppliers still conform to this original specification. The cup-style design has been detailed by Whitcher et al (2014), but for convenience, the salient points are repeated here. As can be seen in figures 1 and 2, the holder is a metal cylinder that is recessed, external diameter roughly 15 mm, internal diameter a little over 10 mm and recessed by 5 mm.…”