125Ba高自旋态的测量

通过¹⁰⁹Ag(¹⁹F,3n)核反应布局了¹²⁵Ba核的激发态.使用带BGO康普顿抑制的高纯锗探测器阵列和常规在束γ实验技术,测量了它的高自旋态.建立在h_11/2中子支壳上的负宇称带和建立在g_7/2中子支壳上的正宇称带分别被延伸到了35/2^－和23/2⁺态.负宇称带显示出明显的正负Signature劈裂,而正宇称带则几乎没有这种劈裂.负宇称正负Signature带均出现反弯,其反弯处转动频率与¹²⁴Ba晕带反弯频率相近.正宇称带出开始出现反弯迹象.     

超越平均场模型对Ba同位素链八极形状演化研究

本文采用超越平均场模型研究了缺中子Ba同位素链114-124Ba的八极形变及其演化规律。计算了Ba链的位能曲面、低能激发谱、电四极跃迁几率、电八极跃迁几率及集体波函数的几率密度分布,并与实验相比较。理论计算较好地再现了Ba核的低能激发结构。位能曲面、低能的负宇称带、较大的B（E3;3₁- → 0₁+）和展宽的几率密度分布表明,114Ba中存在较强的八极关联。116,118Ba具有过渡核特征,而120-124Ba则为典型的四极形变原子核。     

集体运动态中的辛弱数混合

在由S和D核子关联对构成的原子核集体运动态中,存在由辛弱数混合造成的伪态成份. 给出了计算这种伪态成份的公式,并进行计算和讨论.     

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.     

A≈80区奇–奇核80,82Rb的晕带能谱计算

在A≈80区奇-奇核旋称反转问题上已提出几种机制,但没有一种理论推断是结论性的.在本工作中将角动量投影壳模型应用到^80,82Rb核,对组态为πg_9/2⊙νg_9/2的正宇称晕带和组态为π(p_1/2,p_3/2,f_5/2)⊙νg_9/2 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反转机制进行了探讨.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变到高自旋的扁椭球.此外,还确定了此两带的原子核形状     

α结团和集体低位态

核内α结团和集体低位负宇称态早就发现了,但理论上未能很好解释。本文介绍了最近一些典型实验所给出的新信息,老理论似乎更不能完满的解释。人们正在发展老的理论或寻找新的途径,现在α结团问题正在和集体低位态(特别是低位负宇称态)沟通起来,α回弯现象也可将二者联系起来。其结果,可能导至对一些问题的重新认识或甚至解决。所以,这个课题是远离β稳定性核性质和高自旋态的新课题,也是核表面结构的一个大课题。     

原子核的配对壳模型及数值计算(I)

原子核配对壳模型用“真实”的价质子对和价中子对构造组态空间的波函数,包含了单粒子能量项的贡献.在配对壳模型内,费米子运力学对称模型(FDSM)和相互作用玻色子模型(IBM)可以作为它的特殊情况.本文报道这一模型的思想、框架及其数值计算程序.     

1p壳层核的α折合宽度

利用谐振子壳模型波函数,计算了1p壳层核的α折合宽度。计算结果发现,正常宇称能级的理论值与实验值大致相符,反常宇称能级的理论值则比实验值小得多。这表明至少对于反常宇称能级,通常的单量子激发壳模型波函数还不能正确反映原子核的结团现象,它们与原子核真实状态的差别还是很大的。     

转动核的EMC效应

我们讨论了原子核的集体转动对EMS效应的影响,并由此提出了测量核的集体转动流的一种方法.     

关于原子核独立粒子结构的力学基础

本文讨论了原子核独立粒子结构的力学基础问题,指出独立粒子运动的基本因素是体积效应。满壳层附近的每一个核子因为和满壳层内其他核子相互作用的结果,将使周围核物质极化,而在它自己周围形成核子云,因而这个核子的磁矩,有效电荷等将发生一定的变化。但是因为角动量和宇称守恒的关系,这个带有极化核子云的核子的角动量和宇称将不会改变。在原子核内两个核子发生碰撞的几率与原子核体积Ω成反比,三个核子发生碰撞的几率与Ω²成反比,依次类推。这样我们就证明了为什么利用耦合理论计算原子核能级是正确的。并且也证明了壳模型指出的每个核子的角动量和宇称也是正确的。但是我们不能用壳模型波函数来计算原子核的磁矩和跃迁几率。     

Nucleon-pair approximation with uncoupled representation

In this paper, we propose an approach to nucleon-pair approximation(NPA) with m-scheme bases, in which the collective nucleon pairs are represented in terms of antisymmetric matrices, and commutations between nucleon pairs are given using a matrix multiplication that avoids angular-momentum couplings and recouplings.Therefore the present approach significantly simplifies the NPA computation. Furthermore, it is formulated on the same footing with and without isospin.     

Nuclear Shape Transitions and Some Properties of Aligned-Particle Configurations at Very High Spin in Some Rare-Earth Nuclei

We will present results on an collective ΔI = 2 ground band level sequence in the spherical six-valence-particle nucleus ¹⁵²Dy and the variation of shapes for nuclei in the N = 88 to 92 transitional region. Finally, we will present results for some even-even nuclei without any backbending behaviour, showed a clear backbending in the diagram of 2??/?² versus (?ω)².     

Low-lying levels, γ-ray transitions,and vibrational structure in 198Pt from (n,n'γ) reaction spectroscopy

Low-lying states in ¹⁹⁸Pt have been studied by (n, n'γ) reaction spectroscopy at incident neutron energies below 2.5 MeV. Using detailed γ-ray excitation functions and angular distribution measurements, we have established a level scheme which includes 16 excited levels and is believed to include all levels below an excitation energy of 1.5 MeV. The positive-parity structure is similar to that expected for an anharmonic vibrator; however, difficulties in asserting that the first 0⁺ excited level is a collective excitation are encountered. Only two negative-parity states are observed, and they are adequately described in the semi-decoupled model.     

Collective Dand Structures in Doubly Odd 136La Nucleus

Using heavy-ion nuclear reaction and in-beam γ-ray spectroscopy technique,high spin states of ¹³⁶La have been studied. The nuclear reaction used is ¹³⁰Te(¹¹B,5n) with a beam energy 60MeV. The level scheme with three collective band structures has been updated with spin up to 20h. The collective backbending has been observed in $\uppi h_{11/2}\otimes \upnu h_{11/2}$ band. According to the TRS calculations,this backbending is due to the alignment of a pair of h_11/2 neutrons. The signature splitting and inversion for the $\uppi h_{11/2}\otimes \upnu h_{11/2}$ band were also discussed. Other two bands based on $12^-$ and $16^+$ levels were proposed as oblate deformation with $\gamma\approx -60^\circ$. They most probably originate from four- and six- quasiparticle configurations, that is,$\uppi h_{11/2}\otimes\upnu g_{7/2} h_{11/2}^2$ and $\uppi g_{7/2}\otimes\upnu g_{7/2}^2 d_{5/2}h_{11/2}^2$ respectively.     

Backbending in theN=96 isotones

The backbending in the even-even,N=96 isotones can be quantitatively accounted for by the rotation-alignment of the spins of neutrons in i 13/2 orbits, as shown by comparing the aligned angular momentum and relative Routhian for thes-bands in these isotones and for the i 13/2 bands in the corresponding isotopes withN=91. The influence of protons on this backbending situation is shown to be indirect, acting through a change of the nuclear deformation, which yields a change of the moment of inertia of the g.s. band and of the non-rigid character of the rotation. The experimental data on theN=96 and 97 isotones are in reasonable agreement with cranking model calculations. Possible reasons for the inhibition of backbending in the h 9/2 proton bands in the odd-Z, N=96 isotones, all related to a change of deformation, are presented.     

Experimental evidence for low-spin members of “upper” bands in156Dy

Study of the energy levels of¹⁵⁶Dy through the¹⁵⁹Tb(p, 4n)¹⁵⁶Dy reaction has revealed the existence of six states with excitation energies between 1.8 and 2.8 MeV and spins between 6 and 12. Some of them can tentatively be assigned as low-spin members of “upper” bands which are thought to be responsible for the backbending phenomenon experimentally observed in the ground-state andβ-vibrational bands of this nucleus. Others could be levels of a negative-parity octupole band.     

E2 transitions between positive- and negative-parity states of the ground-state alternating-parity bands

Experimental transition probabilities between states of the ground-state alternating-parity bands of ¹⁴⁴Ba and their theoretical analysis are presented. Lifetimes of states in ¹⁴⁴Ba have been measured using the recoil distance method following spontaneous fission of ²⁵²Cf. The experiment was performed at the Lawrence Berkeley National Laboratory employing the Gammasphere array and the New Yale Plunger Device. The experimental data show a significantly larger value of the E2 transition probability between the negative-parity states compared to the positive-parity ones. It is shown that this effect can be explained by a higher weight of the deformed component in the wave functions of the odd-I states. In the framework of the cluster approach it is explained by a higher weight of the alpha-cluster component in the wave function of the negative-parity states compared to the positive-parity ones. In the framework of the traditional collective model with the quadrupole and octupole degrees of freedom the same effect is explained by a higher value of the quadrupole deformation at the minima of the potential energy as a function of β₂₀ and β₃₀ compared to its value at the top of the barrier separating two physically equivalent minima, having opposite signs of the octupole deformation. Additionally, the dependence on parity of the E2 transition probability is analyzed qualitatively in nuclei with a minimum at β₃₀ = 0 in the collective potential energy and compared to experimental data for ¹⁴⁸Nd.     

Coulomb energy differences in t = 1 mirror rotational bands in (50)Fe and (50)Cr

Gamma rays from the N = Z-2 nucleus (50)Fe have been observed, establishing the rotational ground state band up to the state J(pi) = 11+ at 6.994 MeV excitation energy. The experimental Coulomb energy differences, obtained by comparison with the isobaric analog states in its mirror (50)Cr, confirm the qualitative interpretation of the backbending patterns in terms of successive alignments of proton and neutron pairs. A quantitative agreement with experiment has been achieved by exact shell model calculations, incorporating the differences in radii along the yrast bands, and properly renormalizing the Coulomb matrix elements in the pf model space.