Alpha Decay Half-Lives of New Superheavy Elements through Quasimolecular Shapes

The lifetimes of a decays of the recently produced isotopes of the elements 112, 114, 116 and the element ^294118 and of some decay products have been calculated theoretically within the Wentzel-Kramers-Brillouin approximation. The a decay barriers have been determined in the quasimolecular shape path within a generalized liquid drop model including the proximity effects between nuclei in a neck, the mass and charge asymmetry and the precise nuclear radius. These calculations provide reasonable estimates for the observed a decay lifetimes. The calculated results have been compared with the results of the density-dependent M3Y effective interaction and the experimental data. It is indicated that the theoretical foundation of the generalized liquid drop model is as good as that of the microscopic DDM3Y model, at least in the sense of predicting the T1/2 values as long as one uses a correct a decay energy. The half lives of these new nuclei are well tested from the consistence of the macroscopic, the microscopic and the experimental data.     

金红石相纳米块材TiO2的介电特性

研究了不同制备压力下成型的以金红石相为主的纳米二氧化钛介电常数的频率谱和温度谱。在频率谱上发现,当频率ω<0.1kHz时,随着测量频率的下降,介电常数迅速升高,低频下的介电常数比高频区的介电常数高1—2个数量级。并且随着样品加压压力的提高,介电常数升高,在与之相对应的介电损耗谱上,随着样品加压压力的提高,损耗值下降,损耗峰向低频区位移。对1.0GPa压力下成型的样品,其介电常数随测量温度的升高,分别在50℃和300℃出现两个峰值。经分析得出,影响金红石相纳米二氧化钛介电行为的微观机制主要为晶粒内部的电子松弛极化和界面中的电偶极矩的转向极化,50℃峰对应于电于松弛极化,而300℃峰则对应于电偶极矩的转向极化。 关键词：     

α particle preformation and shell effect for heavy and superheavy nuclei

The α particle preformation factor is extracted within a generalized liquid drop model for Z = 84-92 isotopes and N = 126,128,152,162,176,184 isotones.The calculated results show clearly that the shell effects play a key role in α particle preformation.The closer the proton and neutron numbers are to the magic numbers,the more difficult the formation of the α cluster inside the mother nucleus is.The preformation factors of the isotopes reflect that N = 126 is a magic number for Po,Rn,Ra,and Th isotopes,but for U isotopes the weakening of the influence of the N =126 shell closure is evident.The trend of the factors for N = 126 and N = 128 isotones also support this conclusion.We extend the calculations for N = 152,162,176,184 isotones to explore the magic numbers for heavy and superheavy nuclei,which are probably present near Z = 108 to N = 152,162 isotones and Z = 116 to N = 176,184 isotones.The results also show that another subshell closure may exist after Z = 124 in the superheavy nuclei.This is useful for future experiments.     

Unified fission model for proton emission

The unified fission model （UFM） combining with the phenomenological assault frequency has been carried out to investigate the proton-radioactivity half-lives of spherical proton emitters. The results are in good agreement with the experimental data and other theoretical values, and newly observed spherical proton emitters have been analyzed. Finally, the effect of angular momentum transfer on half-life of proton emission has been discussed in detail and a formula can be used to describe this relationship.     

Bi同位素链上原子核α衰变性质的理论研究

采用结团模型(clustermodel)计算了从10752Te到292116共443个核素α衰变的半衰期,所得结果与实验值符合得很好,显示了结团模型可以成功地应用于研究原子核α衰变的性质。同时研究了Bi同位素链上奇A核α衰变的半衰期,计算结果与已有的实验值的偏差一般在3倍以内,进而对实验上未知α衰变半衰期的原子核的性质进行了预言。这有助于将来在实验室探测与鉴别这些原子核以及研究它们的α衰变性质。理论与实验的比较将加深人们对原子核结构的认识。     

超重核294118和291116及其α衰变链上各核素半衰期的研究

运用推广的液滴模型（GLDM）确定了超重核294118和291116及其α衰变链上各核素的衰变势垒, 采用量子力学中的WKB方法计算α衰变中的势垒穿透几率, 对该链上各原子核的α衰变半衰期进行了研究。 此外, 还利用Royer公式对该链上各原子核的α衰变半衰期进行了计算。 结果表明, GLDM 考虑亲和能与Royer公式给出的α衰变半衰期与超重核区的实验值符合很好, 验证了GLDM和Royer公式在超重核区的适用性,可以用来预测超重核的半衰期。 最后, 预言了Z=118 和116 同位素链上各核素的半衰期, 结果表明, 在Z=118和116中存在α衰变长寿命同位素, 这需要实验上的检验。The α decay potential barrier of the newly synthesized superheavy nuclei starting from 294118 and 291116 have been determined and their half lives have been studied with the Generalized Liquid Drop Model(GLDM) connected with WKB approximation and Royer’s formulae．The α decay half lives of the nuclei belonging to the superheavy nuclei starting from 294118 and 291116 have been calculated．The calculated results are in agreement with the experimental data, which show that the α decay half lives of superheavy nuclei with the GLDM and Royer’s formulae can be applied in the studying on superheavy nuclei successfully．Finally, the half lives of Z=118 and 116 isotopes have been predicted, and the results suggest there may be some long lived superheavy nuclei for α decay in those isotopes.     

Properties and structure of N=Z nuclei within relativistic mean field theory

The axially deformed relativistic mean field theory with the force NLSH has been performed in the blocked BCS approximation to investigate the properties and structure of N=Z nuclei from Z=20 to Z=48. Some ground state quantities such as binding energies, quadrupole deformations, one/two-nucleon separation energies, root-mean-square （rms） radii of charge and neutron, and shell gaps have been calculated. The results suggest that large deformations can be found in medium-heavy nuclei with N=Z=38-42. The charge and neutron rms radii increase rapidly beyond the magic number N=Z=28 until Z=42 with increasing nucleon number, which is similar to isotope shift, yet beyond Z=42, they decrease dramatically as the structure changes greatly from Z=42 to Z=43. The evolution of shell gaps with proton number Z can be clearly observed. Besides the appearance of possible new shell closures, some conventional shell closures have been found to disappear in some region. In addition, we found that the Coulomb interaction is not strong enough to breakdown the shell structure of protons in the current region.     

Anomaly in the Charge Radii and Nuclear Structure

The axially deformed relativistic mean field theory is applied to study the isotope shift of charge distributions of odd-Z Pr isotope chain. The nuclear structure associated with the shell and the isotope effect is investigated. The mechanism of the kink in the isotope shift at the neutron magic number N = 82 is revealed to be dependent on the neutron energy level structure at the Fermi energy, demonstrating that the spin-orbit coupling interaction and p-n attraction are well described by the relativistic mean field theory.     

Odd-Even Effects of the Survival Probability for Superheavy Compound Nuclei

The survival probability of the superheavy compound nuclei with Z=114 is studied with the statistical model. It is found that the survival probability shows drastic odd-even effects. The odd-A compound nuclei have higher survival probability by evaporating three neutrons as compared with their neigbouring even-A compound nuclei.     

对超重核基态性质的系统性研究

对有限力程小液滴模型计算的质子数z=101—130超重核同位素链核的基态性质进行了系统的分析，通过对这些同位素链中处于裂变稳定线上核的平均结合能、四极形变、单质子分离能、双质子分离能和a衰变能等性质的系统研究，显示了质子数Z=108，114，126和中子数N=162，180，196时壳幻数的存在，同时可以看到Z=127之后超重核的基态性质还需要进一步研究。The calculated data by the Finite Range Droplet Model (FRDM) for the ground state properties of super-heavy nuclear isotope chains from Z=101 to Z=130 are analyzed in a global systematic way. Some quantities of the super-heavy nuclei which lie on the line of stability agains fission, such as the mean binding energy, deformation, single and double proton separation energy, as well as the α decay energy indicate the existence of the shell closure positions at Z=108, 114 and 126 and N=162...