Characterization of 235 U, 238 U and 239 Pu fission ionization chamber foils by a and y-ray spectrometry

The masses of thin, electroplated deposits of 235 U, 238 U and 239 Pu on titanium backings have been determined to better than 1.3% precision by employing three complementary measurement techniques: a spectrometry, 2K gas counting, and y-ray spectrometry. A dedicated a spectrometer was designed and calibrated to allow for repeatable, high-precision measurements of the absolute a activity of a sample. The isotopic composition of the sample was determined by fitting the peaks in the a spectrum, a technique which was demonstrated to be generally consistent with mass spectrometry. Independently, the total activity of the deposits were measured in a 2K gas flow proportional counter. A detailed study of the effects of a particle straggling in the actinide deposit and a particle recoil off the sample backing material was performed. The masses of these actinide deposits were also measured via y-ray spectrometry. We found that all three systematically independent techniques produced consistent results, and could be combined into a weighted average with further reduced uncertainty. The mass ratios of these actinide deposits were determined to better than 1% precision via a spectrometry, enabling high-precision fission cross section ratio measurements.