  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 Jyv\"askyl\"a. 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.
