Yrast studies ofSe80,82using deep-inelastic reactions

Abstract

We report the results of an experiment in which we studied the near-yrast states in selenium isotopes approaching N = 50 following their population in multinucleon transfer reactions between a 82 Se beam and a 192 Os target. The level schemes for 80,82 Se derived from the current work are compared with restricted-basis shell-model calculations and pair-truncated shell-model calculations. These provide a good description of the yrast sequences in these nuclei using a basis space limited to excitations in the ν(p 3 2 , p 1 2 , g 9 2 ) and π ( The study of neutron-rich nuclei is of significant current interest. Of particular focus is the question of the robustness of magic numbers at N, Z = 28, 40, and 50, and the appearance of subshell closures at nucleon numbers 32 and 34 as a function of neutron/proton number. Single-particle monopole energy shifts between specific orbitals can result in a rearrangement of the traditional ordering of subshells associated with nearspherical nuclei [1,2], which in turn results in the appearance (removal) of new (traditional) magic numbers. Recent reports following initial studies with projectile fragmentation [3][4][5] and deep-inelastic reactions [6][7][8][9] have suggested a possible subshell closure for neutron number N = 32 (and perhaps N = 34), associated with a large single-particle gap between the neutron p 3 2 and p 1 2 orbitals. It has been proposed that a weakening of the proton-neutron π 1f 7 2 → ν1f 5 2 interaction and a significant ν2p 3 2 → ν2p 1 2 spin-orbit splitting result in the appearance of an N = 32 shell closure by lowering the p-shell neutron orbitals in energy with respect to the f 5 2 states. The states are inverted compared to the traditional near-stable ordering in which it is expected that the f 5 2 lies below the p 3 2 and p 1 2 , respectively. Monopole-energy shifts can be inferred from direct measurement of single-particle energies in odd-A nuclei or, alternatively, by identifying configuration-specific decays in the spectral sequences at higher spins [10]. This short article is intended to investigate the proton energy levels above the Z = 28 shell closure for N ∼ 50.The nuclei of interest were populated following heavy-ion, multinucleon transfer reactions with a thick target [8,9,11,12]. The beam of 82 Se ions of energy 460 MeV was provided by the tandem XTU and superconducting LINAC ALPI at the Laboratori Nazionali di Legnaro, Italy. The ions were incident on an isotopically enriched (97.8%) 192 Os target of thickness 50 mg/cm 2 backed with a 0.2 mm layer of Ta, thick enough to stop all the reaction products. Reaction γ rays were measured using the GASP spectrometer [13] consisting of 40 Compton-suppressed, coaxial, hyperpure germanium detectors and an 80 element inner BGO ball for γ -ray multiplicity and calorimetry measurements. Events consisting of at least 3 Compton-suppressed germaniums and 2 BGO elements within an event time of approximately 1 µs were written to tape for off-line analysis. The on-target beam current during the experiment ...

Transition probabilities in neutron-richSe84,86

“…mid-shell isotopes up to the N = 50 shell closure was investigated experimentally and theoretically with great effort [1][2][3][4][5][6]. Recently this work was extended to nuclei with N > 50 [7][8][9].…”

Transition probabilities in neutron-rich Se80,82 and the role of the νg9/2Litzinger1, Blazhev2, Dewald3 et al. 2018Phys. Rev. CSelf Cite5000View full textAdd to dashboardCite

“…[5]. The fact that only a degraded component of the Doppler-shifted 419-keV transition depopulating the excited state at 2784 keV is observed in our data for all distances leads to a lower lifetime limit of τ 105 ps.…”

“…Excitation energies and γ -ray energies are given in keV, taken from NNDC [23] and Ref. [5]. Further details are given in the text.…”

“…In 80 Se, transitions were experimentally identified and assigned as a sideband on top of the yrast 4 + 1 state [5]. In this work, lifetime information is gained for three band members; see 2365-keV, 2784-keV, and 3364-keV levels in Fig.…”

“…and have been investigated with great detail both theoretically and experimentally [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The level schemes of 80,82 Se were investigated and extended recently in multinucleon-transfer and fission experiments [3,9].…”