稀土区高自旋三轴超形变及其形成机制

通过¹⁵²Sm(¹⁹F,4n)¹⁶⁷Lu反应观测到¹⁶⁷Lu的一个新的转动带.发现其高自旋γ跃迁能量与¹⁶³Lu和¹⁶⁵Lu三轴超形变的十分相近.按基于推转壳模型的总转动位能面计算,¹⁶⁷Lu和前人工作中的¹⁷¹Ta[660]1/2转动带被指定为三轴超形变带.讨论了该核区三轴超形变的形成机制.     

三轴超形变核态的研究

首次利用粒子-转子模型描述了¹⁶³Lu、¹⁶⁵Lu和¹⁶⁷Lu三轴超形变带.γ跃迁能量、运动学和动力学转动惯量以及¹⁶³Lu的跃迁四极矩理论值和实验值较好地符合.     

粒子–转子模型分析超形变转动带

利用三轴粒子-转子模型计算了¹⁹³Tl超形变带γ跃迁能量,运动学转动惯量J⁽¹⁾和动力学转动惯量J⁽²⁾,并与实验值进行比较得到了满意的结果;预言了B(M1)值以及动力学电四极矩Q⁽¹⁾和Q⁽²⁾指出在超形变带的分析中粒子-转子模型是一种可以采用的方法.     

168Hf三轴超形变核态的研究

采用TRS方法研究了¹⁶⁸Hf核的三轴超形变核态. 通过位能面计算给出了平衡形变参数, 证实了高自旋态下该核存在三轴不对称性. 通过分析各部分修正能量, 研究了其三轴超形变形成的机制: 主要原因是中子壳修正, 同时高j闯入轨道πi_13/2的形变驱动效应和转动能也起到重要作用.     

偶偶核超形变带唯象分析

利用宏观模型对¹⁹²Hg,¹⁹⁴Hg三条超形变带进行唯象分析,提出了从现有实验数据精确决定超形变带自旋的方法.     

A～190区超形变带能谱分析和自旋的决定

利用宏观模型系统地分析了A～190区七个超形变核十五条超形变带的能谱,决定了超形变带的自旋值,用三参数公式计算了能谱,运动学转动惯量J⁽¹⁾和动力学转动惯量J⁽²⁾,并与实验进行了比较,得到了较满意的结果.     

奇A核超形变全同带分析

利用三轴粒子-转子模型研究了A～190区奇A核超形变全同带,采用标准的BCS方法处理对关联,分析了(¹⁹¹Au,¹⁹¹Hg(b1)),(¹⁹¹Hg(b2),¹⁹³Hg(b2))和(¹⁹¹Hg(b3),¹⁹³Hg(b3))三对全同带,指出特定轨道的填充是造成全同带的重要原因.     

164Lu的三轴超形变核态的研究

利用TRS方法对双奇核¹⁶⁴Lu的位能面进行了计算,确认了¹⁶⁴Lu核的一条三轴超形变带,结果与实验较好地符合,同时指出了三轴超形变带的一个具体的组态     

A=40核区超形变转动带终止

用组态相关推转Nilsson-Strutinsky模型研究了³⁸K, ³⁶Ar, ^32,34S和³⁵Cl的超形变转动带结构性质. 对一些特殊的近转晕线组态的性质做了较为详细的探讨并预言了其带终止态的自旋值, 尤其是预言了³⁸K有利于实验测量到超形变带终止态的自旋值为19h, 而其四极形变值达ε₂～0.50. ³⁶Ar的理论计算与实验结果较好的一致表明这些预言结果是较可靠的.     

175Hf原子核的三轴超形变的探寻

通过采用TRS方法对实验上新发现的¹⁷⁵Hf原子核的两条高自旋转动带进行了研究, 以证明是否具有三轴超形变, 并且为了使结果能够更准确可靠, 选取了最靠近费米面的5个准粒子的组态进行了计算, 但是在这个组态上最后得出的总位能面上并没有发现能表明三轴超形变的明显的第二极小点的存在.     

原子核的三轴超形变

利用粒子 -转子模型研究三轴超形变核态,讨论了区别轴对称超形变和三轴超形变可能的实验信息.为了直接从实验上识别三轴超形变带,必须同时测量能谱和电磁跃迁几率. Current developments in triaxial superdeformed states in nuclei are discussed from a theoretical perspective. A detailed analysis of superdeformed triaxial bands is made with particle-rotor model. Experimental information which may differentiate triaxial superdeformation from axially-symmetric superdeformation is disussed. In order to identify the superdeformed triaxial bands both the energy spectra and electromagnetic transition.     

Study of Triaxial Superdeformation in 162Lu

The triaxially superdeformed states in 162Lu are investigated using the three-dimensional total routhian surface calculation, and the deformation parameters and the likely configuration are given. The shell and pairing correction energies are considered respectively, and the formation mechanism of triaxial superdeformation is investigated.     

Study of Triaxial Superdeformation in ^162Lu

The triaxially superdeformed states in ^162Lu are investigated using the three-dimensional total routhian surface calculation, and the deformation parameters and the likely configuration are given. The shell and pairing correction energies are considered respectively, and the formation mechanism of triaxial superdeformation is investigated.     

Electromagnetic moments of nuclei at high-spin

Choosing some of the current topics in the field of high-spin nuclear physics, I discuss what we learn from the study of electromagnetic moments of the high-spin states. Chosen topics are triaxial shape, superdeformed band, high-spin states with oblate shape, and g-factor before and after band-crossings.     

Searching Triaxial Superdeformation in 175Hf

A two-dimensional Total Routhian Surface(TRS) calculation is carried out in order to ascertain if there is triaxial superdeformation in ¹⁷⁵Hf. A five quasi-particle configuration is chosen in the calculation. Unfortunately, the TRS minimum does not show up in the total potential energy surface.     

Rb晕带signature反转的机理

将角动量投影壳模型应用到84Rb核，对组态为πg9/2νg9/2的正宇称晕带和组态为π(p3/2,f5/2)νg9/2的负宇称晕带理论计算和实验结果进行了比较，特别是对正宇称晕带中的signature反转机理进行了探讨.角动量投影壳模型计算显示正宇称晕带中的signature反转是原子核随自旋增加形状发生变化的信号，其间原子核从低自旋的长椭球通过三轴形变变到高自旋的扁椭球.此外，还确定了此两带的原子核形状.     

质子数Z 分别位于Ru 之上和之下的A~(100~126) 丰中子原子核三轴形变在原子核形状变迁和共存中的重要作用(英文)

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 射线-- 三重符合、特别是新建立的--- 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 MeV), 经具有大三轴形变的Rh核γ=28°),到Pd核中的稍小、但稳定于中等自旋到高自旋区的三轴形变(γ~41°,三轴形变极小增益为0.32 MeV),再经Ag核中的软度,最后到具有很小形变、但仍出现集体性质、包括软三轴形变的Cd核的过渡。对于Pd核转动带交叉系统性的研究揭示了其第一带交叉(νh_11/2)2 中子转动顺排的上行驱动,和第二带交叉(πg_9/2)2质子转动顺排的下行驱动效应,成功地解释了114Pd 中的三轴摆动运动,并给出了110-118Pd同位素链中理论早已预言、而比早期理论预言更为完整准确的形状渐进变迁和形状共存的图像。根据该核区的系统研究,发现最大三轴形变出现在112Ru,而在相邻的偶Z(Pd)同位素链,三轴形变极小的中心在114Pd, 两者均为N = 68。上述系统性研究沿相邻的Ru和Pd偶Z同位素链,在N =68同中素中鉴别出最大三轴形变,均比理论预言的108Ru 和110Pd 多4个中子。在Z值位于Ru (Z = 44) 之下的Zr (Z = 40), Nb (Z = 41), Mo (Z = 42) and Tc (Z = 43) 丰中子同位素中,Y和Zr核具有很强的轴对称四极形变,而在较重的Zr同位素中出现了自由度;较重的Nb核(A = 104~106) 基态具有中等程度的软三轴形变和强四极形变,随着自旋和激发能的增加,过渡到接近于轴对称的强四极形变;而较轻的Nb核(A≤103) 基态均接近轴对称形状;在Nb同位素链上基态由球形到强四极形变的形状突变发生在100Nb(N = 59),在100-106Nb同位素链中基态的软三轴形变随中子数增加而增加;在Nb核中还观察到关于软三轴形变的形状共存;Mo核具有大的三轴形变,观察到了振动和手征对称破缺;Tc核具有比最大值稍小的三轴形变,γ=26°,并观察到了手征对称破缺。质子数Z从41到48的A~(100~126)丰中子同位素,特别是Pd和Nb 同位素,呈现出关于三轴形变的过渡特征。This paper reviews the systematic investigations and understanding for the shape transitions and coexistence with regard to triaxial deformations in A s 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-γ and 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, respectively,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 122,124,126Cd in the vicinity of Z =50 and N = 82 closed shells by studies of Coulomb excitations; shape evolutions from maximal triaxial deformations in Ru (γ=30°, with triaxial minimum energy gain of 0.67 MeV), through Rh with large triaxial deformations ( γ=28°), to less pronounced triaxiality in Pd (with triaxial minimum energy gain of 0.32 MeV), then soft triaxiality in Ag, and finally to slightly deformed Cd isotopes but with emergence of collectivity and soft triaxiality were proposed. The systematic studies of the band crossings in Pd revealed up-rising drivings of the first band crossings caused by (νh_11/2)2 and down-sloping drivings of the second band crossings by (πg_9/2)2, explained the onset of wobbling motions in 114Pd,and showed a long-sought picture of shape evolution and coexistence in the Pd isotopic chain which is more complete but complex than earlier predictions. Based on the systematic studies in the mass region,maximal triaxial deformation is found to be reached in 112Ru and less-pronounced triaxiality centered at 114Pd, both for N =68, four neutrons more than predicted in earlier theoretical calculations.In the neutron-rich Zr (Z =40), Nb (Z =41), Mo (Z =42) and Tc (Z =43) isotopes with Z just below Ru, large quadrupole deformations of axially symmetric shapes were deduced in Y and Zr isotopes, with emergence of the degree of freedom having been suggested for heavier Zr isotopes; medium triaxial deformations were deduced for the ground states of heavier (A > 104) Nb isotopes, and, with increasing excitations and spins, evolution from medium triaxial deformations with strong quadrupole deformations at ground states to nearly axially-symmetric shapes were deduced; light Nb isotopes (A6103) have near axially-symmetric shapes with strong quadrupole deformations; combining with the identification of onset of strong quadrupole deformation at 100Nb in the Nb isotopic chain, an increase of soft triaxiality with increasing neutron number was proposed in 100-106Nb. Shape coexistence with regard to soft triaxiality is also proposed in Nb isotopes; large triaxial deformations, vibrations and chiral doublets were proposed in Mo isotopes; chiral doubling and large triaxial deformations (γ ~26°) slightly smaller than the maximal triaxiality were suggested in Tc isotopes.The neutron-rich nuclei with Z ranging from 41 through 48 and A ~100 to 126, especially the Pd and Nb isotopes are thus found to be transitional nuclei with regard to triaxiality.     

Os-Pt区核的基态三轴形状

在偶-偶核基态中寻找稳定的三轴形状,其中最大三轴形变为|γ|≈30°,仍然是核结构的一个主要主题。在本工作中,使用推转Woods-Saxon(WS)壳模型来研究Os-Pt区基态和集体转动态中可能的三轴形状。为寻找核态可能存在的三轴形变,具体用对力-形变-转动频率自洽推转壳模型对偶-偶^176-202Os和^182-204Pt同位素进行了总Routhian面计算。计算是在四极形变(β₂,γ)网格中进行的,而十六极形变β₄可变。事实上,在四极形变(β₂,γ)的每个网格点上,计算的能量相对于十六极形变β₄最小化。发现某些核的基态譬如¹⁹⁶Os和^188-194Pt既非扁椭球亦非长椭球,而是在这些核中基态极小值是形状非轴对称的,即三轴形变。同时,我们把从实验数据提取出的转动惯量与我们的计算结果作比较,显示实验数据不能很好地与转动假定相一致,说明有振动行为。此外,我们使用一种辅助的方法提取了平衡γ₀值,该值...