Excited states in Br87 populated in β decay of Se87

Abstract

Excited levels in 87 Br, populated in β decay of 87 Se, have been studied by means of γ-ray spectroscopy using an array of broad energy Ge detectors. 87 Se nuclei were produced by irradiating a natural Th target with 25-MeV protons. Fission products were extracted from the target chamber using the IGISOL technique, then separated on a dipole magnet and Penning trap (JYFLTRAP) setup. The scheme of excited levels of 87 Br has been significantly extended. 114 new transitions and 51 new levels were established. β feedings and log(f t) values of levels were determined. The upper limit for β feeding to the ground state of 87 Br was determined to be 23(5)%. Ground state spin and parity 5/2 − was confirmed, as suggested by previous studies. We also confirm the low-energy excited state at 6.02 keV. The ground state and two lowest excited states in 87 Br were interpreted as the (π f 5/2) 3 j, j−1, j−2 triplet produced by the so-called anomalous coupling. The 333.61-and 699.26-keV levels were interpreted as π p 3/2 and π p 1/2 single-particle excitations. The 9/2 + level reported previously as corresponding to the π g 9/2 single-particle excitation is proposed to be an isomer with half-life 20 ns. Large-scale shell-model calculations performed in this work are in good agreement with experimental results.

Medium-spin states of the neutron-rich nucleus Br87

“…Our analysis agrees with Ref. [4] and provides unique spin-parity assignments for the 6, 801, 2226, and 3098 keV levels. A I = 2 band based on the π g 9/2 configuration is expected to appear at relatively low energy in 87 Br with a bandhead spin-parity of 9/2 + based on the deformed Nilsson scheme and also on the comparison with the level schemes of the neighboring odd-proton nuclei.…”

“…Preliminary results from our study on the excited states of the odd-proton 87 Br have been reported in a conference proceedings [3]. Several levels and tentative spin-parities of these results have been confirmed by a new study on the lowspin states of 87 Br from β decay of 87 Se, published recently [4]. The ground-state spin-parity has been assigned as 5/2 − in agreement with the tentative assignment of Ref.…”

“…The levels up to the 1464 keV one and the transitions depopulating them have been confirmed by Ref. [4]. The obtained level energies, spin-parities, γ -ray energies and relative intensities, as well as the γ -ray branching ratios are given in Table I.…”

“…Using the multipole character of the transitions in 87 Br derived in this work and the unique spin-parity assignments reported in Ref. [4], together with information on the level schemes of neighboring odd-proton nuclei, we propose spinparity values for levels in 87 Br as shown in Table I and in Fig. 2.…”

“…In this level scheme we extended Bands 1 and 3 by one level each, and adopted the 333 keV level from Ref. [4] compared to the level scheme in Ref. [3].…”