中文摘要：

基于Ru(Z=44)丰中子同位素中存在最大三轴形变的理论预言和实验证据,综述了近年来Rh(Z=45),Pd(Z=46),Ag(Z=47),Cd(Z=48)(质子数Z位于Ru,Z=44之上)及Zr(Z=40),Nb(Z=41),Mo(Z=42),Tc(Z=43)(质子数Z位于Ru,Z=44之下)的A～(100～126)丰中子同位素中关于三轴形变的形状变迁和形状共存系统性研究的重要进展。252Cf自发裂变瞬发γ射线γ-γ-γ三重符合、特别是新建立的γ-γ-γ-γ四重符合数据的系统观测和研究,在Ru,Pd,Cd和Nb丰中子同位素中显著扩展或首次观测到了一系列能带,为这个核区原子核形状的研究提供了新的、重要的实验数据。联系此前报道的有关进展,使用PES,TRS,PSM,CCCSM和SCTAC理论模型计算拟合新的实验数据,在该核区沿同中素和同位素链,并随自旋和激发能变化各自由度,跟踪原子核形状渐进变化,获得了新的系统性研究成果,显著扩展和深化了人们对原子核形状变迁和形状共存的认知。对于Ru及其上的Rh(Z=45),Pd(Z=46),Ag(Z=47)和Cd(Z=48)丰中子同位素的研究表明:Rh丰中子核具有比最大值稍小的三轴形变,γ=-28°,并在103–106Rh同位素链上鉴别出了手征对称破缺;在三轴形变核112Ru和114Pd(N=68)中发现了三轴原子核的摆动运动,该摆动运动也可能在114Ru(N=70)中存在;观察到了从具有最大三轴形变的110,112Ru中手征破缺到稍小三轴形变的112,114,116Pd中扰动的手征破缺的过渡;在较软的Ag核中观察到了丰富的谱学结构,在104,105Ag中鉴别出了可能的手征对称破缺,在较重的115,117Ag中提出了趋于三轴形变的γ软度;具有小形变的Cd核的能级结构被解释为准粒子耦合、准转动和软三轴形变;最近的库伦激发的研究提供了Z=50,N=82满壳附近122,124,126Cd核中出现核集体性的实验和理论证据;上述研究成果展现出从Ru中的最大三轴形变(γ=-30°,三轴形变极小增益为0.67 Me V),经具有大三轴形变的Rh核(γ=-28°),到Pd核中的稍小、但

英文摘要：

This paper reviews the systematic investigations and understanding for the shape transitions and coexistence with regard to triaxial deformations in A ～100 to 126 neutron-rich Rh (Z=45), Pd (Z=46), Ag (Z=47), Cd (Z=48) and Zr (Z=40), Nb (Z=41), Mo (Z=42), Tc (Z=43) isotopes with Z beyond and below Ru (Z = 44), respectively, in Ru the maximal triaxial deformation having been predicted and deduced. The recent measurements and studies of prompt triple-and four-fold,γ-γ-γand γ-γ-γ-γ, coincidence data from the spontaneous fission of 252Cf using Gammasphere have yielded considerable expansion and extension or first observation of the bands in Ru, Pd, Cd, and Nb isotopes, which provided important data for the studies of nuclear shapes in this region. Combined with previous investigations, recent systematic studies of the new data well reproduced by PES, TRS, PSM, CCCSM and SCTAC model calculations have traced shape changes along the isotonic and isotopic chains, re-spectively, and with changing excitations/spins as well, significantly expanding our knowledge of shape transitions/coexistence in nuclei.
For the neutron-rich Ru and beyond, Rh, Pd, Ag and Cd isotopes, triaxial deformations γ=?28°, slightly smaller than the maximal value, were deduced in Rh (Z =45) isotopes, with chiral symmetry breaking proposed in 103?106Rh;onset of wobbling motions were identified in 112Ru and 114Pd (N=68), and probably also in 114Ru (N=70);evolution from chiral symmetry breaking in 110,112Ru with maximal triaxial deformations to disturbed chirality in 112,114,116Pd with less pronounced triaxial deformations was proposed; rich nuclear structure was proposed in soft Ag isotopes with possible chiral doubling structure suggested in 104,105Ag, and softness towards triaxial deformation proposed in heavier 115,117Ag;quasi-particle couplings, quasi-rotations and soft triaxiality were suggested in Cd (Z=48) isotopes with small deformations;onset of collectivity was recently suggested in 122,124,126 Cd in the vicinity of Z=50