  We present the results of a measurement of isotopic concentrations and atomic
number ratio of a double-sided actinide target with alpha-spectroscopy and mass
spectrometry. The double-sided actinide target, with primarily Pu-239 on one
side and U-235 on the other, was used in the fission Time Projection Chamber
(fissionTPC) for a measurement of the neutron-induced fission cross-section
ratio between the two isotopes. The measured atomic number ratio is intended to
provide an absolute normalization of the measured fission cross-section ratio.
The Pu-239/U-235 atom number ratio was measured with a combination of mass
spectrometry and alpha-spectroscopy with a planar silicon detector with
uncertainties of less than 1%.
