Insight into nuclear midshell structures by studying K isomers in rare-earth neutron-rich nuclei

Abstract

Inspired by the newly discovered isomeric states in the rare-earth neutron-rich nuclei, high-K isomeric states in neutron-rich samarium and gadolinium isotopes are investigated within the framework of the cranked shell model (CSM) with pairing correlation treated by a particle-numberconserving (PNC) method. The experimental multi-particle state energies and moments of inertia are reproduced quite well by the PNC-CSM calculations. A remarkable effect from the high-order deformation ε6 is demonstrated. Based on the occupation probabilities, the configurations are assigned to the observed high-K isomeric states. The lower 5 − isomeric state in 158 Sm is preferred as the two-proton state with configuration π 5 2 + [413]⊗π 5 2 − [532]. More low-lying two-particle states are predicted. The systematics of the electronic quadrupole transition probabilities, B(E2) values along the neodymium, samarium, gadolinium and dysprosium isotopes and N = 96, 98, 100, 102 isotones chains is investigated to reveal the midshell collectivities. * hext@nuaa.edu.cn arXiv:1808.03945v1 [nucl-th] 12 Aug 2018The rare-earth neutron-rich nuclei lie in the midshell region between the closed shells of proton Z = 50, 82 and neutron N = 82, 126. The high spin spectroscopy of these nuclei can provide important insights into the midshell collectivity, changes in nuclear shape and deformed sub-shells in a less-explored single-particle spectrum region. Furthermore, the pygmy rare-earth peak at A ∼ 160 of the r−process abundance is believed to arise from strong midshell nuclear deformation [1,2]. The nuclear structure inputs of the rare-earth nuclei can lead to an improved understanding of the r−process nucleosynthesis [3]. However, due to their neutron excess, detailed structure informations are very difficult to be revealed by the experiment in these rare-earth neutron-rich nuclei.The recent experimental progresses in the neutron-rich A = 150 − 170 region [4][5][6][7][8][9][10][11][12][13] are attributed to a great extent to the existence of the nuclear isomeric state. A nucleus can be "traped" in an aligned spin orientation relative to its symmetric axis to form the K isomeric state (or K-isomer), where K is a quantum number representing the projection of the total nuclear spin along the symmetry axis of the nucleus. K-isomer arises from the multi-particle state, of which the transition to a lower energy state with a different K value is inhibited by the ∆K ≤ λ selection rule where λ is the multipole order of the transition. However, symmetry-breaking processes make these transitions possible to process with the ∆K − λ related hindrance factor [14,15]. The multi-particle state is formed by breaking pairs of nucleon. The excitation energy and configuration of multi-particle state depend strongly on the position of the specific single-particle orbitals near the Fermi surface and correlations, such as pairing. K-isomer appears only in axially symmetric deformed nuclei well away from the closed shell. This implies that K-isomer cannot be a pure intrinsi...

Configuration and bandhead spin assignments for the two-quasiparticle rotational bands in the neutron-rich nuclei Pm154,156

“…In the present work, the cranked shell model (CSM) with pairing correlations treated by a particle-number conserving (PNC) method [24,25] will be used for investigating the rotational bands in these Pm isotopes, and the configuration and bandhead spin assignments will be made for the three 2-qp bands observed in 154,156 Pm. Note that PNC-CSM has already been used for the systematic investigation of the high-K isomers and high-spin rotational bands in the neighboring neutron rich Nd (Z = 60), Sm (Z = 62) and Gd (Z = 64) isotopes [26,27], in which the experimental data are reproduced quite well. Therefore, the calculations for Pm isotopes by PNC-CSM should be quite reliable.…”

High-K multi-particle bands and pairing reduction in 254No *

“…To investigate the pairing reduction due to rotation and blocking, particle-number conserving method (see Refs. [34][35][36][37][38] for details) is employed to deal with the pairing correlations. The cranked shell model Hamiltonian Eq.…”

Effects of high-$j$ orbitals, pairing and deformed neutron shells on upbendings of ground-state bands in neutron-rich even-even isotopes $^{170-184}$Hf

“…The details of the PNC-CSM method can be found in Refs. [22,[26][27][28][29]. [30] (black squares) and in 2016 [31] (red solid circles) for the even-even isotopes 170−184 Hf.…”