Structure of 0+ excitations in the mass A≈100 region: 02+ bands in

W. Urban

¹

,

T. Rza̧ca‐Urban

²

,

Jarosław A. Wiśniewski

³

et al.

Abstract

+ 2 bands in 98 Sr and 100 Zr, populated in spontaneous fission of 248 Cm and 252 Cf have been studied using Eurogam2 and Gammasphere arrays. Phenomenological classification of excited 0 + levels in even-even nuclei of the A∼100 region into four categories is presented and an interpretation for each category is proposed. Highly-deformed, 0 + 1 ground states and low-energy, 0 + 2 levels in both nuclei are probably due to the 2p-2h excitation of two neutrons from the 9/2 − [404] extruder to the low-Ω, prolate and the 11/2 − [505], oblate orbitals originating from the h 11/2 shell, respectively. Candidates for 0 + , β vibrational states in A∼100 region are suggested at N>60.

First observation of γ -soft and triaxial bands in Zr isotopes

“…The ground-state band and bands on top of the 331.32-keV and 2130.6-keV levels are drawn after Ref. [2], where previous studies of 100 Zr [11] are also discussed. Properties of γ lines and excited levels in 100 Zr, new compared to Ref.…”

“…Properties of γ lines and excited levels in 100 Zr, new compared to Ref. [2], are listed in Table I. Intensities of these transitions are in the same relative units as shown in Table II of Ref.…”

“…Intensities of these transitions are in the same relative units as shown in Table II of Ref. [2], with the intensity of the 212.67-keV line normalized to 100. In the scheme we report a new band build on top of the 2244.7-keV level and new levels at 2208.5, 2471.8 and 2776.0 keV with their decays, as shown in Fig.…”

“…Half a century after reporting strong, prolate deformation in even Zr isotopes with N≥60 [1] these nuclei can still surprise. Our recent work [2] indicates that the structure evolution in these nuclei is more complex than just a prolate deformation occurring at N≈60. The nearly spherical 0 + 2 state in 100 Zr corresponds to an oblate configuration with a 2p-2h leading component, where a pair of neutrons is promoted from the 9/2 + [404] "extruder" to the 11/2 − [505] orbital, downsloping on the oblate side.…”

“…The same 9/2 + [404] extruder lends two neutrons to the low-Ω orbital of the νh 11/2 shell, downsloping on the prolate side, producing the 0 + 1 , ground-state configuration with a strong prolate deformation. The local appearance of the 9/2 + [404] orbital at N≈60 [3][4][5][6] explains the local presence of oblate configurations as well as the sudden increase of prolate deformation in 98 Sr and 100 Zr [2]. This local effect is superimposed on the gradual evolution of prolate deformation in the 50<N<66, 36<Z<50 region caused by the interaction of ground-state 0 + levels with collective, excited 0 + levels.…”