title: Development and evaluation of a collection apparatus for recoil products for study of the deexcitation process of (235m)U.
abstract: The nucleus (235m)U 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 (235m)U depends on its chemical environment. We plan to study the deexcitation process of (235m)U 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 (235m)U samples from (239)Pu 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 (224)Ra recoiling out of (228)Th electrodeposited and precipitated sources. The pressure in the apparatus (vacuum or 1 atm of N2 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 (228)Th sources. From these results, the suitable conditions of the (239)Pu sources for preparation of (235m)U were determined. In addition, dissolution efficiencies were determined by washing collected (224)Ra with solutions. When (224)Ra was collected in 1 atm of N2 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 (235m)U samples for various chemical forms.
authors.affiliation: Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Shigekawa
authors.affiliation: Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kasamatsu
authors.affiliation: Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Shinohara