原子核壳模型发现前后

 大约四十年前,梅耶和詹森分别独立地提出了原子核壳模型,成功地解释了幻数等原子核结构的主要特性.虽然这个模型并未最终解决原子核结构问题,但它应作为研究原子核结构的基础模式已为世人所公认.因此,梅耶、詹森和对群论在核谱学上的应用作出重大贡献的魏格纳一起荣获了1963年度诺贝尔物理学奖金。本文介绍发现原子核壳模型的前后经过.卢瑟福发现原子内有核存在在1906年卢瑟福发现α粒子散射现象以后,盖革和马斯顿做了大量α粒子散射的研究工作.     

基于相对论Hartree-Fock理论的原子核壳结构性质研究

一直以来,原子核壳结构是原子核物理研究的重点关注内容。特别是随着近年来新一代放射性核束装置和探测技术的蓬勃发展,丰中子原子核中新的壳结构及其演化与形成机制等成为核物理关注的热点之一。在基于核力介子交换图像建立的相对论Hartree-Fock 理论框架下,本工作以Ca同位素、双幻核 208Pb、超重核以及极端丰中子核为例,综述丰中子原子核中新的壳结构形成机制,高角动量态赝自旋对称性恢复与介质中核力吸引-排斥平衡,赝自旋对称性恢复/破缺与原子核壳结构、新奇现象等研究工作,并着重关注了与原子核新壳结构形成、赝自旋对称性恢复以及新奇现象等密切相关的交换(Fock)项效应。     

核破裂中的激发能的作用

在晶格气体模型的框架中研究了¹²⁹Xe系统在破裂过程中的热力学性质和轻粒子发射性质随核温度和系统的冻结密度的变化规律.计算发现在不同的冻结密度下,¹²⁹Xe破裂过程的物理观测量呈现了不同的温度相关性.在这种情况下,核物质液气相变发生时的临界温度强烈地依赖于系统的冻结密度.当激发能代替温度作为一个自变量时,临界激发能将不再灵敏地依赖于系统的冻结密度.除此之外,由于不同冻结密度而引起的不同粒子发射产额的温度相关性,也随着激发能的应用,出现了几乎一致的激发能依赖性.从这些结果中可以认为,激发能可以作为一个控制核破裂的基本物理量和标度量.     

原子核集体运动的新模式

 由Z个质子和N个中子(统称核于)构成的原子核,在一些场合下表现出独立粒子运动的特征,在另一些场合下表现出A个核子(A=Z+N)集体运动的特征,这两种运动形态又常常相互影响,相互耦合.本文着重介绍原于核集体运动的若干新模式.首先介绍集体振动的新模式.     

原子核高角动量激发

用推转壳模型计算研究了原子核的高速转动运动及其结构特性.讨论了A～50区核的转动特性;A～80$区(N=Z)核的形状共存问题; A～110$区丰中子核的扁椭球形变的稳定性. 基于壳模型理论, 我们用限制组态绝热堵塞方法计算讨论了A～130, 180和超重核区的高角动量同核异能态,系统预言了高角动量多准粒子态的存在, 并指出这些核态可以有较长的寿命, 这对于不稳定核的研究是很有帮助的. 计算解释了不少典型的实验观测, 一些理论预言已经被最近的实验证实.     

35MeV/u 40Ar+197Au反应中复合核的激发能与温度

利用大面积位置灵敏气体探测器对35MeV/u ⁴⁰Ar+¹⁹⁷Au反应中形成的裂片进行了符合测量,由此得到了裂变复合核的速度分布.在大质量转移假设下扣除前平衡发射粒子的影响,得到复合核的激发能.另外利用望远镜探测器对反应中出射的轻带电粒子也进行了符合测量,并由后角α,p,d,t的能谱提取了复合核的温度.温度与激发能的关系没有表现出理论预言的相变特征.     

原子核145Tb的多准粒子激发

利用能量为165MeV的³²S束流, 通过熔合蒸发反应¹¹⁸Sn(³²S, 1p4n), 布居了¹⁴⁵Tb的高自旋态. 基于标准在束核谱学实验测量结果, 首次建立了¹⁴⁵Tb的高自旋态能级纲图. 根据邻近N=80同中子素能级结构的系统性, 用弱耦合模型对¹⁴⁵Tb的低位能级结构进行了解释. 本工作在多粒子壳模型组态基础上对¹⁴⁵Tb的更高激发态进行了深入讨论. 为了使实验能级的组态指定更为直接方便, 采用了参数无关的半经验壳模型计算. 其结果清楚地揭示了球形核多准粒子的激发特性.     

25MeV/u~(40)Ar ~(93)Nb反应中热核的激发能和核温度

利用半导体望远镜探测器和ＰＰＡＣ对２５ＭｅＶ／ｕ４０Ａｒ＋９３Ｎｂ反应中的带电粒子和余核进行了关联测量，对所得α粒子能谱用三源模型进行了拟合，并由余核飞行时间和粒子多重性得到热核激发能．通过对温度的修正，发现在本实验中有激发能Ｅ＊／Ａ为４．３ＭｅＶ，温度Ｔｉｎｉｔ为６．９ＭｅＶ的热核形成。通过与其它实验结果的对比可以看出核物质在轻系统和重系统中行为的差异。     

同位旋激发能研究

在扩展的Skyrme有效相互作用下,利用Hartree-Fock理论研究了同位旋激发能与温度、密度的关系.结果表明同位旋激发能随密度的降低以及温度的增加而降低.同时研究了对称能与同位旋激发能的关系,指出对称能是同位旋激发能的一部分,且占相当大的比重.最后研究了不同的势参数下,同位旋激发能随相对中子过剩的变化关系,发现同位旋激发能较强地依赖于对称能强度系数,而对不可压缩系数以及有效质量不太敏感.从而为实验上通过研究同位旋激发能来提取核物质状态方程中的对称能部分指出了一条途径.     

随机相互作用的原子核等多体系统的性质

讨论了随机相互作用下原子核等多体系统的基态和低激发态性质研究方面的进展情况。 In this paper it is discussed the regularities of many body systems such as nuclei in the presence of random interaction. In particular,it concentrates on the present status towards understanding of spin zero ground state dominance,energy centroids of certain quantum number(s) such as spin, behavior of low lying states,under random interactions.     

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.     

热核表面能的Thomas－Fermi统计模型理论

用Ｓｅｙｌｅｒ－Ｂｌａｎｃｈａｒｄ动量相关非定域相互作用的含温Ｔｈｏｍａｓ－Ｆｅｒｍｉ统计理论，对半无穷大核物质模型计算了核物质表面能系数σ（Ｔ，δ）随温度Ｔ和不对称度δ的变化，发现在低温Ｔ≤５ＭｅＶ和不对称度δ≤０．２时，可以近似写成σ（Ｔ，δ）＝σ０（Ｔ）［１＋Ｋ（Ｔ）δ２］，其中σ０（Ｔ）和Ｋ（Ｔ）可以拟合成温度Ｔ的二次函数．     

激发能相关的能级密度参数和重核衰变性质(英文)

基于裂变的随机模型,研究了能级密度参数在鞍点与其基态处的比值a_f/a_n在热核衰变过程中的作用。计算表明,a_f/a_n的大小能显著影响蒸发剩余截面及其自旋分布的大小以及裂变过程中热核的耗散行为。发现,能级密度参数对激发能的依赖性a_f/a_n(E*) 能改变断点处的激发能对摩擦强度的敏感性。最后指出了a_f/a_n随E* 的变化对超重核的稳定性和散裂反应退激阶段描述的意义。Based on the stochastic approach to fission, we have demonstrated that the ratio of level-density parameters at saddle to that at ground-state configuration, af/an, plays a significant role in the decay of an excited nucleus. It modifies not only the sensitivity of evaporation residue cross section and its spin distributionsto nuclear friction, but also the dissipation properties of hot nuclei. Furthermore, we find that af/an as a function of excitation energy appreciably affects the evolution of excitation energy at scission with the friction strength. A consequence of a change of af /an with E* on the stability of superheavy nuclei and on modelling de-excitation processes of spallation reactions is indicated.     

中能轻奇异核反应总截面的激发函数测量

通过对中能区和相对论能区反应总截面的比较, 可对了解核中核子密度分布的尾巴分量提供重要的信息, Ｇｌａｕｂｅｒ 模型的计算总是低估中能区的反应总截面, 对中子晕核和中子皮核, 这种低估更为严重． 因此, 基于 Ｇｌａｕｂｅｒ 模型从反应总截面提取核的大小存在着一些问题． 对一些轻的奇异核进行中能区核反应总截面的激发函数测量可能会有助于上述问题的解决.A comparison of interaction cross section at relativistic and intermediate energy provides important information about the existence of tail component in the density distribution. The Glauber model calculation always underestimates the total reaction cross section at intermediate energy. The differences are enhanced for halo and skin nuclei. The method to extract the size of nuclei via Glauber model seems to have some ambiguity. The excitation function of total reaction...     

Energy Radiation of the Active Galactic Nuclei

In the Hellings-Nordtvedt theory, we obtain some expressions of energy radiation and mass defect effect for a kind of the active galactic nuclei, which is meaningful to calculating the energy radiation in the procession of forming this kind of celestial bodies. This calculation can give some interpretation for energy source of the jet from the active galactic nuclei.     

Statistical Behaviors of Quantum Spectra in Superheavy Nuclei

From the point of view of the interplay between order and chaos, the most regular single-particle motion of neutrons has been found in the superheavy system with Z ＝ 120 and N ＝ 184 based on the Skyrme-Hartree-Fock model and in the system with Z ＝ 120 and N ＝ 172 based on the relativistic mean-field model. It has been shown that the statistical analysis of spectra can give valuable information about the stability of suprheavy systems. In addition it may yield deep insight into the single-particle motion in the mean field formed by the superheavy system.     

The Fourth-Order Symmetry Energy of Finite Nuclei

The fourth-order symmetry energy E_sym,4(A) of heavy nuclei is investigated based on the Skyrme energy density functional in combination with a local density approximation. Unlike some previous works, in our method, the interferences from the other energy terms are removed since it is completely isolated from the rest of energy terms. The calculated E_sym,4(A) is much less than that extracted from nuclear masses. The underlying reason for the big difference is discussed. The Brueckner theory also gives a small fourth-order symmetry energy coefficient of nuclear matter, which is also different from recent conclusions with another methods.     

原子核的反常宇称能谱研究

将具有负宇称的 fp 空间扩大到包含1g9/2 轨道, 采用修正的表面相互作用(MSDI), 对64Ge, 66Ge, 68Ge, 70Se, 72Se, 74Se, 76Kr 和 78Kr等偶偶核作了形变Hartree Fock计算, 得到了基态和一些激发态的解. 同时, 还用近似角动量投影形变Hartree Fock（PDHF）方法对偶偶核64Ge, 74Se和奇A核79Kr进行了能谱计算, 得到其正、 负宇称带的解, 计算结果与实验谱基本一致.Using modified surface delta interaction, enlarging the fp configuration space to include the 1g9/2 orbit with the abnormal parity, the deformed Hartree Fock calculations for the eight nuclei: 64Ge, 66Ge, 68Ge, 70Se, 72Se , 74Se, 76Kr and 78Kr are performed. The ground state and some particle hole excited configurations are obtained. The approximate angular momentum projected deformed Hartree Fock (PDHF) method is applied to even even nuclei 64Ge and 74Se and odd A nuclus 79Kr. Both of their normal and abnormal parity bands are obtained. The calculated energy spectra are consistent well with experimental spectra.