High-spin structure in the transitional nucleus Xe131 : Competitive neutron and proton alignment in the vicinity of the N=82 shell closure

Abstract

The transitional nucleus 131 Xe is investigated after multinucleon transfer in the 136 Xe + 208 Pb and 136 Xe + 238 U reactions employing the high-resolution Advanced γ -Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and as an elusive reaction product in the fusion-evaporation reaction 124 Sn( 11 B,p3n) 131 Xe employing the High-efficiency Observatory for γ -Ray Unique Spectroscopy (HORUS) γ -ray array coupled to a double-sided silicon strip detector at the University of Cologne, Germany. The level scheme of 131 Xe is extended to 5 MeV. A pronounced backbending is observed at hω ≈ 0.4 MeV along the negative-parity one-quasiparticle νh 11/2 (α = −1/2) band. The results are compared to the high-spin systematics of the Z = 54 isotopes and the N = 77 isotones. Large-scale shell-model calculations employing the PQM130, SN100PN, GCN50:82, SN100-KTH, and a realistic effective interaction reproduce the experimental findings and provide guidance to elucidate the structure of the high-spin states. Further calculations in 129−132 Xe provide insight into the changing nuclear structure along the Xe chain towards the N = 82 shell

Quadrupole deformation of Xe130 measured in a Coulomb-excitation experiment

“…In particular, the GCN50:82 interaction shows good agreement for the neighboring Xe isotopes 131 Xe [48], 132 Xe [49], and 133 Xe [50].…”

“…The calculations were undertaken using the KSHELL program [47]. Both shell-model approaches have successfully reproduced experimental results for a range of isotopes in this mass region, namely 135,136,137 Ba and 131,132,133,135 Xe [31,44,[48][49][50][51].…”

Isomer spectroscopy in Ba133 and high-spin structure of Ba134

“…A J π = 23/2 + isomers (T 1/2 = 33(3) ns [12]) is known in 129 Te. Adding four protons, the level scheme of 131 Xe was recently extended to approximately 5 MeV [13]. The first J π = 19/2 + state at 1805 keV, decaying via a 189.2-keV γ ray into the J π = 19/2 − state, has been identified as an isomer with an adopted half-life of 14 (3) ns [14].…”

“…However, a precise half-life of the 1942-keV state was not evaluated; the half-life was constrained to be between 2 and 5 ns. Later, the level scheme was significantly extended by Juutinen et al [20], using 13 C-induced reactions and the NORDBALL γ -ray array. In total, nine collective bands up to 7 MeV were observed.…”

“…The only evaluated data on high-spin states [50] refers to a preliminary level scheme from a JYFL (Accelerator Laboratory of the University of Jyväskyl) annual report by Lönnroth et al [51] in 1990. In that study, two parallel cascades on top of the J π = 10 + isomer were identified using a 13 C + 124 Sn reaction inside the NORDBALL γ -ray spectrometer. Besides that result, two high-spin level schemes from works utilizing 14 C + 124 Sn and 9 Be + 130 Te reactions [52,53], respectively, differ significantly from each other as well as from evaluated data [50,51].…”