Characterization of 233U alpha recoil sources for 229(m)Th beam production

Abstract Radioactive 233 U alpha recoil sources are being considered for the production of a thorium ion source to study the low-energy isomer in 229 Th with high-resolution collinear laser spectroscopy at the IGISOL facility of the University of Jyvaskyla. In this work two different 233 U sources have been characterized via alpha and gamma spectroscopy of the decay radiation obtained directly from the sources and from alpha-recoils embedded in implantation foils. These measurements revealed rather low 229 Th recoil efficiencies of only a few percent. Although the low efficiency of one of the two sources can be attributed to its inherent thickness, the low recoil efficiency of the second, thinner source, was unexpected. Rutherford backscattering spectrometry (RBS) was performed to investigate the elemental composition as a function of depth revealing a contamination layer on top of the thin source. The combination of spectroscopic methods proves to be a useful approach in the assessment of alpha recoil source performance in general.