Structure of Be Hyper Isotopes

The low-lying level structure of ${^{10}_\Lambda{\rm Be}}$ and ${^{12}_\Lambda{\rm Be}}$ has been studied by using the antisymmetrized molecular dynamics for hypernuclei (HyperAMD). In these hypernuclei, it is interesting to reveal the changes of excitation spectra by adding Λ hyperon, because the ground and low-lying states with different deformation coexist in ⁹Be and ¹¹Be. Based on the HyperAMD calculation, it is found that the first excited state 1/2⁺ of ⁹Be is shifted up by about 700 keV in ${^{10}_\Lambda{\rm Be}}$ . In ${^{12}_\Lambda{\rm Be}}$ , the parity-inverted ground state of ¹¹Be is reverted by adding Λ hyperon. In this article, we discuss the reason for these structure changes related to the coexistence of ground and low-lying states with different deformation.     

The Structure of the Neutron-Rich Nd Isotopes in the IBM

The spectra and E2 transition properties of ^146-156Nd isotopes are studied in the interacting boson model in the light of new experimental data. It is found that ^146-150Nd are in the transition from the vibrational limit to the rotational limit. From ¹⁵²Nd onward, the isotopes are nearly perfect rotors. Possible deformation saturation is discussed in the interacting boson model.     

Triaxiality in Neutron-Rich As Isotopes with Covariant Density Functional Theory

The relativistic mean-field model with density-dependent DD-ME2 and DD-PC1 interactions has been used for the investigation of the ground-state shape evolution of neutron-rich ^83–91 As isotopes. For this purpose, the potential energy curve and the potential energy surface of each nucleus of interest have been examined. From analyzing the potential energy surfaces of the neutron-rich ^83–91 As isotopic chain, ⁸⁷ As is suggested to be a possible candidate for triaxial nucleus. Furthermore, studies of some ground-state nuclear properties of As isotopes such as energy, size and deformation have been obtained.

     

Impact of Tensor Interaction on Beta-Delayed Neutron Emission from Neutron-Rich Nickel Isotopes

The Skyrme energy density functional including tensor interaction is used to describe microscopically multineutron delayed-neutron emission accompanying beta decay of even–even neutron-rich nickel isotopes of mass number in the range of A = 74?80. The respective calculations are performed in the quasiparticle random-phase approximation with allowance for the two-phonon components of the wave function for states of the daughter nucleus. The properties of the lowest quadrupole excitation of ^74,76,78,80Ni are also studied. It is shown that a decrease in the strength of neutron–proton tensor interaction leads to a substantial hindrance of beta decay and to an increase in the probability for delayedneutron emission.     

丰中子Zn核素奇特核结构讨论和展望

不稳定核结构是当前核物理研究的前沿热点问题之一,尤其是针对丰中子幻数核附近的区域。中子数N=40, 50附近镍区域核素展现出丰富的结构特征,激励了众多理论和实验研究。原子核的基本性质与核的结构密切相关,这里我们选择分析丰中子Zn(Z=30)同位素的基本性质来进一步了解这一核区的核结构特征。本文回顾了在欧洲核子中心(CERN)的ISOLDE测量Zn 同位素的实验,基于62–80Zn 核素基态和长寿命同核异能态的自旋、磁矩、电四极矩以及电荷均方根半径等基本性质,并结合各种大规模壳模型计算结果,系统地讨论了这一核区的壳结构演化、幻数特征、奇特形变和形状共存,以及核子间关联激发等物理现象。最后,基于已有的实验数据和物理现象,以及理论预言的 N=50以上镍核区的能级演化特征,我们提出在ISOLDE的共线共振电离谱装置上测量更加丰中子的81,82Zn 核素基本性质的实验设想。     

Ground State Structure of Hs Super-heavy Isotopes

The ground state properties of Hs nuclei studied in the framework of the relativistic mean field theory revealed that more stable isotopes are located on the proton abundant side of the chain.The last stable nucleus to the proton drip line is ~(256)Hs.The most stable unknown Hs nucleus may be ~(268)Hs.The density dependent delta interaction pairing is used to improve the BCS pairing correction,which results in more reasonable single-particle energy level distributions and nucleon occupation,and it is shown to be available to describe the properties of nuclei in the superheavy region.     

Pb核性质和残余相互作用

在壳模型的框架中,用MSDI和K-H相互作用作为中子空穴间的残余相互作用.计算和讨论了Pb(A=204,205,206)的结构性质;对MSDI和K-H相互作用的结果作了较全面的比较,比较结果表明,MSDI也是一种很好的残余相互作用,可以很好地应用于描述铅区核的性质.另外,还讨论了直接从实验值来检验和判定两体矩阵元的方法.     

Intermediate Energy Coulomb Excitation of Neutron-Rich Nuclei

We reinvestigate the collective effects of the retardation as well as the bending on the Coulomb excitation cross sections and also on the B（E2） strengths of some neutron-rich isotopes using the intermediate energy Coulomb excitation theory. It is found that the B（E2） strengths extracted from the experimental Coulomb excitation cross section data get suppressed approximately by 6%. Furthermore, the obtained B（E2） strengths in the energy range 30-100 MeV/A are found to be in better agreement with the corresponding values known from other sources, than those obtained by using the recoil-corrected relativistic Coulomb excitation theory.     

Cross Section Measurements of Neutron-Rich Hg Isotopes in Reaction of 28MeV/u 18O with Thick Natural Lead Target

By using 28MeV/u ¹⁸O beam,an on-line melting lead target equipment and 4π-ΔEβ-γcoincident technique,the relative cross section ratios and absolute cross sections of neutron-rich nuclides ^205—208Hg have been measured. The production cross section of ²⁰⁹Hg is extrapolated.The cross section of ²⁰⁷Hg produced by-2p +1n from target decreases suddenly,which may be explained by change of reaction Q value.     

Three-Body Forces and Neutron-Rich Exotic Nuclei

Physics of three-body forces in connection to exotic nuclei will be discussed. Three-nucleon forces (3NF), especially Fujita–Miyazawa 3NF, are shown to be the key for the solution to the long-standing problem of oxygen drip line, which deviates from basic trend towards the stability line. Three-body forces produce repulsive modifications to effective interaction between valence neutrons, and make the ground states less bound. The oxygen drip line is then located at the right place. The relation to the neutron matter is presented. Applications to Ca isotopes will be presented. The shell evolution due to the 3NF depicts the raising of single-particle energies and the widening of splitting among the orbits. This is in contrast to the so-called shell quenching. The 2⁺ levels are calculated for Ca isotopes, suggesting about the same sub-magic structure for N = 32 and 34.     

轻丰中子核的壳模型计算

对9≤A≤14,3≤Z≤5的核进行了壳模型计算.以⁸He作为core,选用修正的表面δ相互作用(MSDI)作为残余相互作用,挑选了24个实验能谱数据,定出了MSDI的参数和单粒子能量,并计算了结合能、低激发谱、电磁性质等,得到与实验较符合的结果.并着重讨论了¹¹Be的宇称反转和halo结构的物理机理.计算程序为OXBASH.     

Inelastic proton scattering on Neutron-Rich sulphur isotopes

The proton scattering on unstable³⁸S nuclei has been measured in inverse kinematics by using a³⁸S secondary beam at 39 MeV/nucleon. The first 2⁺ state is seen at 1.2 MeV excitation energy and its angular distribution is extracted. Optical and folding model calculations are compared with the elastic and the 2 ₁ ⁺ angular distributions and the β₂ value is determined to be 0.35±0.04. This value is compared with the corresponding result from a Coulomb excitation measurement and theM _n/M_p value is extracted.     

丰中子核145,147La的八极形变

通过对²⁵²Cf自发裂变产生的瞬发γ谱的实验研究,建立与扩展了丰中子核^145,147La的高自旋态能级图,最高自旋态达到(41/2⁺)与(43/2^－).测得的交叉相联的相反宇称带及带间的强化E1跃迁说明在^145,147La中形成强的八极形变.对¹⁴⁵La的研究表明,具有轴对称形状的四极形变与具有反演不对称形状的八极形变在同一核中产生共存与竞争.在πh_11/2带中观测到的带交叉位于ω≈0.26—0.30MeV附近,由推转壳模型计算表明,它是由一对i_13/2中子的顺排所引起的.     

丰中子核107Ru的集体转动带

通过对²⁵²Cf自发裂变产生的瞬发γ谱的测量,对丰中子奇A核¹⁰⁷Ru的高自旋态集体转动带重新进行了研究,建立了新的能级纲图.将基带转动带的自旋态扩展到27 2h,证实并扩展了以前发表的基于中子h_11/2激发产生的集体转动带,并新观测到一个基于(9/2^－)能级的集体转动带.研究结果澄清了早期发表的结果与近来别人发表的结果之间的矛盾,对新建立的¹⁰⁷Ru能级结构的某些重要特征进行了讨论.