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

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 2024-06, Vol.1063 (C), p.169234, Article 169234
• Main Authors: Silano, J.A., Malone, R.C., Finch, S.W., Gooden, M.E., Howell, C.R., Ramirez, A.P.D., Thomas, K., Tonchev, A.P., Tornow, W., Wilhelmy, J.B.
• Format: Article
• Language: English
• Subjects: Alpha spectrometry; Fission ionization chambers; Gamma spectrometry
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2024.169234

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