Spectroscopy of neutron deficient 65Ge

Abstract

Excited states of 65 Ge were populated via the 12 C + 58 Ni (261 MeV) reaction using the NORDBALL detector array equipped with charged-particle and neutron detector systems for reaction channel separation. On the basis of γγ-coincidence relations and angular distribution ratios a significantly extended level scheme was constructed up to E x = 9 MeV and J π = (33/2 − ). The low-energy states of the nucleus are discussed in the framework of the interacting boson-fermion model. : 21.10.Hv; 23.20.Lv; 21.60.Fw; 27.50.+e Using the 12 C( 58 Ni,αn) 65 Ge reaction excited states in 65 Ge were studied. Previously only 10 γ rays were assigned to this nucleus, forming a high energy cascade with some branchings at low energy [1]. In the present work a 1.5 mg/cm 2 thick 12 C target was bombarded with a beam of 261 MeV 58 Ni provided by the tandem accelerator facility of Niels Bohr Institute, Denmark. The emitted γ rays were detected in the NORDBALL detector system, which consisted of 15 BGOshielded Ge detectors, a 30-element γ-ray calorimeter of BaF 2 crystals, 11 neutron detectors covering a solid angle of about 1π in the forward direction and a 4π charged-particle detector array consisting of 21 ∆E type Si detectors [2]. A total of 120 million γγ-charged particle-neutron coincidence events were collected, from which γγ matrices were created by applying different gating conditions set on the number of detected protons, α particles and neutrons. PACSThe level scheme of 65 Ge was established mainly on the basis of coincidence relations. The order of the transitions in the γ-ray sequences was deduced from the intensity relations.The level scheme obtained is shown in Fig. 1. The main branch of γ rays in the level scheme is in agreement with the previous study [1] but the 462 keV transition was relocated. Several weaker branches were found between the known levels, and short cascades of γ rays feeding both the low-and the highlying states were added.The spins were determined from the angular distribution ratios, I γ (143 o )/[I γ (79 o ) + I γ (101 o )], and from the known 3/2 − spin-parity value of the ground state [1] assuming that the γ rays take away the maximum possible angular momenta. Definite parities were assigned to the excited states, if one of their deexciting transitions were stretched E2 or mixed M1/E2 transitions, while in the case of pure dipole transitions only tentative parities were ascribed. The 1105 keV stretched quadrupole transition, decaying from the 1215 keV isomeric state, was accepted to have M2 multipolarity on the basis of the recommended upper limits for the transition strength in agreement with [1].The states below 3 MeV were described in the interacting boson-fermion model (IBFM) [3]. The interacting boson model (IBM) [4] parameters of the 64 Ge core were fitted to the energies of its excited states. The parameters obtained are h 1 = 0.87, h 2 = −0.1, h 3 = 0, h 40 = 0.1, h 42 = −0.25, h 44 = 0.35 (all in MeV). The total boson number was N = 4, which is equal to the number of nucleon pairs in the...