Identification of deformed intruder states in semi-magicNi70

Abstract

The structure of semi-magic 70 28 Ni 42 was investigated following complementary multinucleontransfer and secondary fragmentation reactions. Changes to the higher-spin, presumed negativeparity states based on observed γ-ray coincidence relationships result in better agreement with shell-model calculations using effective interactions in the neutron f 5/2 pg 9/2 model space. The second 2 + and (4 + ) states, however, can only be successfully described when proton excitations across the Z = 28 shell gap are included. Monte-Carlo shell-model calculations suggest that the latter two states are part of a prolate-deformed intruder sequence, establishing an instance of shape coexistence at low excitation energies similar to that observed recently in neighboring 68 Ni.

Enhanced low-energy γ-decay strength of Ni70 and its robustness within the shell model

“…70 Ni exhibits a complex low-energy structure. The second excited state is J π = 0 + at E(0 + 2 ) = 1567 keV [50], and cal-culations indicate it has a very different structure from the ground state [49]. For the CA48MH1 interaction we find good agreement with experiment by increasing the single-particle energy of the νg 9/2 orbital to 1.7 MeV.…”

“…[33]; for the NLD, we make use of known, discrete levels of 70 Ni taken from Refs. [48][49][50]. and Hartree-Fock-Bogoliubov plus combinatorial (HFB-c) calculations taken from Ref.…”

Investigating the γ decay of Ni65 from particle- γ coincidence data

“…Further, the experimental results for 68 Ni indicate the presence of a subshell closure at N = 40 [13][14][15][16], although shell model calculations estimate a rather small (≈2 MeV) gap allowing for cross-shell excitations at low and moderate spins [17]. In addition, recent measurements supported by Monte Carlo shell model calculations suggest a triple-shape coexistence [18,19], also expected for 70 Ni [20,21]. The experimental study of γ decay in the Ni isotopes has been a fundamental tool for the understanding of both singleparticle and collective excitations [6][7][8][9][10][11][12].…”

Neutron single-particle strengths at N=40 , 42: Neutron knockout from Ni68,70 ground and isomeric states

“…219 (1) 6.1(11) 304 (1) 10.8 (22) 379(2) 3.3(13) 594 (1) 100.0 (54) 602.4 (4) 7.5 (26) 1129 (2) 32.4(21) 1196 (2) 15.3 (29) 1319(5) 10.3 (26) 1345(2) 16.0(27) 1545 (4) 17.7 (26) 1582(3) 18.8 (28) 1642(3) 8.3 (10) 1822(2) 61.9 (23) 054324-3 The theoretical partial and inclusive cross-section calculations follow Refs. [38,39].…”

“…This leads to deformation that may enhance specific configurations, for instance, those that are characterized by a higher neutron occupancy of the g 9/2 and d 5/2 orbitals. Recent relevant information on 67−70 Ni stems from a number of measurements using a wide variety of experimental techniques, such as β decay, deep-inelastic reactions, searches for isomeric states, and transfer reactions [1,11,12,[19][20][21][22][23][24][25].…”