中重核中单粒子与集体运动的竞争效应（英文）  

Competition Between the Single-particle Seniority Regime and Collective Motion in Intermediate-mass Nuclei

作　　者：亓冲[1] QI Chong(KTH Royal Institute of Technology,SE-10691 Stockholm,Sweden)

机构地区：[1]瑞典皇家工学院物理系

出　　处：《原子核物理评论》2018年第4期420-428,共9页Nuclear Physics Review

基　　金：Swedish Research Council(VR)(621-2012-3805,621-2013-4323);Gran Gustafsson Foundation~~

摘　　要：从原子核的电四极跃迁强度B(E2)中可以提取出原子核集体性和单粒子性质竞争的重要信息,其中一个重要的观测量是B(E2; 4_1^+→2_1^+)/B(E2; 2_1^+→g.s.)的比值(B_(4/2))。B_(4/2)一般要大于1,而且对于原子核转动和振动,我们应有B_(4/2)=1.4和2.0,但球形半满壳核一般会有不一样的性质。这些核的性质主要受对关联效应影响。介绍了几种超出我们一般认识的奇特衰变性质。Te同位素的基态带有鲜明的振动特性,但114Te的E2跃迁性质却更符合转动性。这些性质可以通过大规模壳模型计算来描述。对于填充j=9/2轨道的半满壳核,它们的4+和6+显示出很强的辛若数部分守恒性质。这种奇特的部分守恒可以被解析证明。而且我们的计算表明辛若数部分守恒对相关的E2跃迁影响很大。对于N=90附近具有量子相变行为的核素,其B_(4/2)也会也表现出相似的奇异特性。The E2 transition strength, B(E2), gives particularly precise information on the competition between the collective and single-particle degree of freedom. An important observable to study the development of collectivity is the B(E2;4++1→2+1)/B(E2;21→g.s.)(B4/2). The B4/2 ratio is usually greater than unity. These values are 1.4 and 2.0 for an ideal rotor and a vibrator, respectively. Whereas the seniority scheme usually leads to different behaviours. In this contribution I will show examples that contrast with our standard understanding. The yrast spectra of Te isotopes show a vibrational-like equally-spaced pattern but the few known E2 transitions show anomalous rotational-like behaviour, which cannot be reproduced by collective models. Large-scale shell model calculations reproduce well the equally-spaced spectra of those isotopes as well as the constant behaviour of the B(E2) values in114 Te. For nuclei involving protons or neutrons in j=9/2 orbitals, the partial conservation of seniority can lead to dramatic changes to the E2 decay pattern that have never been seen before. The B4/2 ratios in quantum phase transitional nuclei around N =90 also show a similar exotic feature.

关 键 词：电磁跃迁 壳模型 辛若数 集体性 

分 类 号：O571.6[理学—粒子物理与原子核物理] P142.9[理学—物理]