Development and evaluation of a collection apparatus for recoil products for study of the deexcitation process of U-235m

作者：Shigekawa Y^*; Kasamatsu Y; Shinohara A

来源：Review of Scientific Instruments, 2016, 87(5): 053508.

DOI：10.1063/1.4950900

The nucleus U-235m is an isomer with extremely low excitation energy (76.8 eV) and decays dominantly through the internal conversion (IC) process. Because outer-shell electrons are involved in the IC process, the decay constant of U-235m depends on its chemical environment. We plan to study the deexcitation process of U-235m by measuring the energy spectra of IC electrons in addition to the decay constants for various chemical forms. In this paper, the preparation method of U-235m samples from Pu-239 by using alpha-recoil energy is reported. A Collection Apparatus for Recoil Products was fabricated, and then collection efficiencies under various conditions were determined by collecting Ra-224 recoiling out of Th-228 electrodeposited and precipitated sources. The pressure in the apparatus (vacuum or 1 atm of N-2 gas) affected the variations of the collection efficiencies depending on the negative voltage applied to the collector. The maximum values of the collection efficiencies were mainly affected by the thickness of the Th-228 sources. From these results, the suitable conditions of the Pu-239 sources for preparation of U-235m were determined. In addition, dissolution efficiencies were determined by washing collected Ra-224 with solutions. When Ra-224 was collected in 1 atm of N-2 gas and dissolved with polar solutions such as water, the dissolution efficiencies were nearly 100%. The method of rapid dissolution of recoil products would be applicable to rapid preparation of short-lived U-235m samples for various chemical forms. Published by AIP Publishing.

• 出版日期2016-6