Rotational bands in the semi-magic nucleus⁵⁷₂₈Ni₂₉

Abstract

Abstract. Two rotational bands have been identified and characterized in the proton-magic N = Z + 1 nucleus 57 Ni. These bands complete the systematics of well-and superdeformed rotational bands in the light nickel isotopes starting from doubly-magic 56 Ni to 60 Ni. High-spin states in 57 Ni have been produced in the fusion-evaporation reaction 28 Si( 32 S,2p1n) 57 Ni and studied with the γ-ray detection array Gammasphere operated in conjunction with detectors for evaporated light charged particles and neutrons. The features of the rotational bands in 57 Ni are compared to those of neighbouring isotopes and interpreted by means of configurationdependent cranked Nilsson-Strutinsky calculations. The two observed high-spin bands are considered signature partners and assigned to configurations with one 1g 9/2 proton and one 1g 9/2 neutron, resulting in an unambiguous understanding of the energetically favoured signature α = −1/2 band but a somewhat less satisfactory description of the signature α = +1/2 band.

Single-particle and collective excitations in63Ni

“…Figure 7(b) illustrates the angular momentum gain I x vs rotational frequency for selected bands in 56 Ni (SD2 in [32,33]), 57 Ni (SD1 in [34,35]), 58 Ni (B3 in [37]), 59 Ni (B2 in [39]), and 60 Ni (W D2 in [41]): all are close to the trajectory of the ν(g 9/2 ) 2 excitation in 60 Fe. In fact, configurations assigned to the respective bands in [57][58][59][60] Ni include at least two particles (protons and/or neutrons) in the g 9/2 orbitals while, for band SD2 in 56 Ni, the configuration involves a single g 9/2 proton.…”

“…From the discussion above, it is clear that an interpretation within the framework adopted for the description of most of the collective bands observed in the Ni [32,33,35,37,39,41] and Zn [52][53][54][55][56] isotopic chains is warranted. Hence, calculations were performed within the configuration-dependent cranked Nilsson-Strutinsky (CNS) model with the formalism described in Refs.…”

“…7. (Color online) Spin along the rotational axis I x vs rotational frequency ω for (a) bands D1, D2, and D3 in 63 Ni and the ground-state band in 60 Fe (GSB in [21]); (b) selected rotational bands in 56 Ni (SD2 in [32,33]), 57 Ni (SD1 in [34,35]), 58 Ni (B3 in [37]), 59 Ni (B2 in [39]), and 60 Ni (W D2 in [41]) together with the trajectory of the yrast band in 60 Fe in the I = 8-20 range, where this sequence is associated with a configuration with two aligned g 9/2 neutrons; (c) same as (b), but for selected bands in 60 Zn (SD in [53]), 61 Zn (SD in [54]), 62 Zn (SD in [55] and SD1 in [56]), and 65 Zn (SD1 in [52]). See text for details.…”

“…Rotational sequences have been reported at moderate and high spin in some of the lighter even-even Ni isotopes: highly deformed and even superdeformed bands, built upon lower-lying single-particle excitations, have been observed in doubly-magic 56 Ni [32,33], as well as in 57 Ni [34,35], 58 Ni [36][37][38], 59 Ni [39], and 60 Ni [40,41]. Remarkably, partial proton and alpha decays out of some of these bands have been reported in 56 Ni and 58 Ni.…”

Single-particle and collective excitations inNi62

“…Studies of high-spin states provide complementary information about the influence of the underlying shell structure on collective excitations. Rotational sequences have been reported at moderate and high spin in some of the Ni isotopes: highly-deformed and even superdeformed bands, built upon lower-lying single-particle excitations, have been observed in doubly-magic 56 Ni [12,13], as well as in 57 Ni [14,15], 58 Ni [16][17][18], 59 Ni [19], 60 Ni [20,21], and 63 Ni [22]. Most of the bands have been associated with configurations involving the alignment of the spin of several particles with the rotational axis.…”