Identification of the(9/2+to(5/2−transition inSe69

Abstract

Gamma rays from ${}_{}{}^{69}{}_{}{}^{}\mathrm{Se}$ have been investigated using the reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ ${(}^{32}$S,2pn γ${)}^{69}$Se between 80 and 110 MeV beam energy. Isotopic identification was based on excitation functions, n-γ and n-γ-γ coincidences, as well as genetic relationships. An isomeric state ($T_{1/2}$=853±78 ns) was found at 575.0±0.4 keV decaying to the first excited state which was located at 40.2±0.3 keV. The isomeric state lifetime reveals the same degree of inhibition as in analogous M2 ${\left(\right(9/2\mathrm{}}^{+}$→${(5/2\mathrm{}}^{\mathrm{-}}$) transitions and the excitation energy displays the systematic trend of the first ${(9/2\mathrm{}}^{+}$ state in the N=35 and N=37 isotones. The observed γ decay properties are consistent with $J^{\pi }$ ${=(3/2\mathrm{}}^{\mathrm{-}}$ for the ${}_{}{}^{69}{}_{}{}^{}\mathrm{Se}$ ground state, in agreement with the indications given by previous beta decay studies. A first level scheme, including four levels in ${}_{}{}^{69}{}_{}{}^{}\mathrm{Se}$, is proposed.