A simple model for doublet bands in doubly odd nuclei

Abstract

Abstract. Nuclear structure of doublet bands in doubly odd nuclei with mass A ∼ 130 is investigated within the framework of a simple model where the even-even core couples with a neutron and a proton in intruder orbitals through a quadrupole-quadrupole interaction. The model reproduces quite well the energy levels of doublet bands and electromagnetic transitions. The staggering of the ratios B(M 1; I → I − 1)/B(E2; I → I − 2) of the yrast bands turns out to be described by the chopsticks-like motion of two angular momenta of the unpaired neutron and the unpaired proton when they are weakly coupled with the core. One of the most intriguing phenomena discussed in medium and heavy nuclei is the appearance of the nearly degenerate doublet bands in doubly odd nuclei. Such pairs of bands built on the νh 11/2 ⊗ πh 11/2 configuration have been experimentally found in many doubly odd nuclei in the mass A ∼ 130 region [1][2][3][4][5][6]. Previously these bands were interpreted as a manifestation of the chiral doublet bands [7]. However, many of recent experiments and analyses do not support this interpretation [8][9][10][11][12]. Recently, we have proposed a pair truncated shell model (PTSM) where the even-even core made of the collective pairs couples with a neutron and a proton in high-j intruder orbitals [13][14][15]. The PTSM successfully describes the properties of doubly odd nuclei in the mass A ∼ 130 region, i.e., both energy spectra and features of electromagnetic transitions. Now the band structure of the doublet bands is well explained by the chopsticks-like motion of two angular momenta of the odd neutron and the odd proton, weakly coupled with the core. Since the PTSM results are rather complicated to analyze, we need a further simplified model to pinpoint the essential mechanism more closely.In this letter we propose a quadrupole coupling model (QCM) where the even-even collective core couples with a neutron and a proton in the high-j intruder orbitals through a quadrupole-quadrupole interaction, and we apply this model to the doublet bands in the mass A ∼ 130 region. In the region, several valence proton particles and a e-mail: yoshinaga@phy.saitama-u.ac.jp valence neutron holes are coupled to the doubly magic nucleus 132 Sn. In the QCM, the states of doubly odd nuclei (neutron number N and proton number Z) with the νh 11/2 ⊗ πh 11/2 configuration are assumed to be constructed by a neutron hole, a proton particle in the 0h 11/2 intruder orbitals, and a collective core. The core is assumed to be made of N + 1 neutrons and Z − 1 protons. A system of one neutron hole in the orbital j ν and one proton particle in the orbital j π is specified as the state |j ν j π ; L , where L is the angular momentum of the particle-hole state. The collective-core state is denoted as |R , where R indicates the angular momentum of the core state. In the simplest version of the model we assume that the neutron and the proton outside the core couple only with the yrast states of the core. Then, a total wave function of any doubly o...

The systematic observation of doublet bands and a validity of their interpretation as chiral doublets

“…frame based theories. Theoretical works of the latter category are the quasi-particle core coupling model using Kerman-Klein method [40], variations of particle-hole plus triaxial rotor model [28,36,41,42], Pair Truncated Shell Model (PTSM) [43], quadrupole coupling model [44], Interacting Boson Fermion Fermion Model (IBFFM) [45] and Interacting Vector Boson Model (IVBM) [46].…”

Chiral geometry in multiple chiral doublet bands

“…Theoretically, many approaches have been come up to investigate nuclear chirality, such as the particle rotor model (PRM) [1,25,30,[58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76], the tilted axis cranking model (TAC) [1,[77][78][79], the tilted axis cranking plus random phase approximation (TAC+RPA) [39,80], the interacting boson fermion-fermion model (IBFFM) [37,40,[81][82][83][84], pair truncated shell model (PTSM) [85][86][87], projected shell model (PSM) [88]. Recently, based on the TAC, a microscopical collective Hamiltonian was constructed and applied to the unified description of chiral vibration and rotation [89].…”

Band structure of doubly-odd nuclei around mass 130

“…In order to investigate such a pair of bands in a simple and unified way, we have recently introduced the quadrupole coupling model (QCM) [10][11][12][13] where the collective core representing the even-even part of the nucleus couples with one neutron and one proton in intruder orbitals through a quadrupole interaction. Theoretical investigations of the doublet bands in the mass A ∼ 130 region were carried out in terms of the QCM [10,11].…”

“…Theoretical investigations of the doublet bands in the mass A ∼ 130 region were carried out in terms of the QCM [10,11]. The model reproduced experimental energy spectra and features of electromagnetic transitions with good accuracy.…”