原子核的结团性质

原子核结团现象是原子核运动中普遍存在的现象。本文评述了原子核结团模型研究的进展和结团思想在核结构性质、核衰变、核反应方面引人注目的发展。     

原子核的结团性质

原子核结团现象是原子核运动中普遍存在的现象,本文评述了原子核结团模型研究的进展和结团思想在核结构性质、核衰变、核反应方面引人注目的发展． Clustering phenomena exist in all the field of the nucleus. In this paper the development of the cluster model and its use in nuclear structure, nuclear radioactivity, and nuclear reactions are described.     

铅以上核结团放射性再研究(英文)

在密度依赖的结团模型下重新研究了铅以上原子核的结团放射性。根据由核电荷半径以及中子皮厚度的实验数据所提炼的子核和结团密度分布，通过双折叠模型得到了关键的结团-核芯作用势。然后结合库仑波函数边界条件求解了结团-子核相对运动的薛定谔方程，以得到衰变宽度。和我们以往没有考虑子核和结团密度具体分布的计算结果相比，现在得到的结团放射性衰变宽度明显增大。另外，随着结团中心越来越高的密度压低，衰变宽度的计算值会减小。We revisit the cluster emission from trans-lead nuclei within the density dependent cluster model. According to the refined density distribution of daughter and cluster via the available experimental data on nuclear charge radii and neutron skin thickness, the crucial cluster-core potential is constructed by the double-folding model. Then the Schrödinger equation of the cluster-core relative motion is solved along the outgoing Coulomb wave function boundary condition to obtain the decay width. The present decay width of cluster radioactivity is clearly augmented as compared to our previous results without the specific concern of the density distribution of daughter and cluster. Moreover, the computed decay width reduces along with the increasingly depressed density in the cluster center.     

原子核结团的非局域化运

原子核中结团的形成是原子核多体动力学的一个重要表现方面,同时它也是核物理中最有 趣的现象之一,对原子核中结团运动和结团结构的研究一直以来就是核物理研究的重要课题。本 文中,我们介绍了原子核结团研究的历史背景和一些重要的结团模型。同时,我们阐述了最近提 出的一个结团物理中的新概念—非局域化结团。我们认为原子核中的结团是非局域化的,它们可 以在整个原子核内做自由的非局域化运动,只是由于泡利阻塞效应而不能靠的太近,这是与传统 的局域化结团概念截然不同的一种观点。非局域化结团的概念使我们加深了对原子核中结团关联 的理解,同时也为探索更为复杂的原子核结团结构提供了一条新的途径。     

密度依赖的结团模型研究原子核的α衰变和结团放射性

讨论了原子核α衰变和结团放射性的一个新的结团模型:密度依赖的结团模型（DDCM）。DDCM基于微观真实的核势和库仑势,可以在统一的框架下计算原子核的各种衰变模式的半衰期。通过对原子核α衰变和结团放射性的系统计算,发现DDCM能够精确给出原子核α衰变和结团放射性的半衰期,理论值和实验值的偏差一般在3倍以内。这表明密度依赖的结团模型具有很好的适用性并可以为将来的实验提供较准确的预言。We have discussed a new cluster model of α-decay and cluster radioactivity: the density-dependent cluster model （DDCM）, which is based on the microscopic nuclear potential and Coulomb potential. DDCM can give accurate theoretical half-lives for various decays of nuclei in a unified framework. Through a systematical calculation of half-lives of α-decay and cluster radioactivity, we find that the deviation between DDCM and experiment is usually less than a factor of 3. This good agreement shows that the density-dependent cluster model can further provide reliable predictions for future experiments.     

基于结团形成模型系统研究Z=82,N=126闭壳附近原子核的α衰变

基于结团形成模型（cluster-formation model,CFM）系统地研究了质子数Z=82,中子数N=126闭壳附近的α衰变母核的α衰变预形成因子P_α。计算结果表明:基于结团形成模型计算得到的P_α线性地依赖于价质子（空穴）N_p和价中子（空穴）N_n的乘积。这与前期工作[SUN X D,et al.Phys Rev C,2016, 94 （2）:024338;DENG J G,et al.Phys Rev C,2017, 96 （2）:024318]得到的结论是一致的,其中,P_α是唯象的且模型依赖的,从α衰变半衰期的理论值和实验值的比值中提取。结合前期工作可以得到这样的结论:对于Z=82,N=126闭壳附近的α衰变母核,其P_α与N_pN_n呈线性关系,且价质子-价中子相互作用在α结团预形成中起了很重要的作用。In the present work, the α decay preformation factors P_α are systematically studied within the cluster-formation model (CFM) for nuclei around Z=82, N=126 closed shells. The calculations show that the P_α calculated by CFM is linearly dependent on the product of valance protons (holes) and valance neutrons (holes) N_p N_n. It is consistent with our previous works[SUN X D, et al. Phys Rev C, 2016, 94 (2):024338; DENG J G, et al. Phys Rev C, 2017, 96 (2):024318], which P_α are model-dependent and extracted from the ratios of calculated α decay half-lives to experimental data. Combining with our previous works, we confirm that the P_α is linearly dependent on the N_pN_n for nuclei around Z=82, N=126 shell closures. In addition, the valance proton-neutron interaction plays a key role in the α preformation.     

重自共轭原子核中α凝聚体物理性质的理论研究(英文)

原子核多体系统中可以存在一类被称为α凝聚体的奇异物理态。该奇异态可以被视为玻色-爱因斯坦凝聚在原子核物理中的推广。一般认为,α凝聚体不仅可以存在于12C中,也可以存在于诸如16O,20Ne,24Mg,28Si等质量更重的自共轭原子核中。重自共轭原子核中的α凝聚体的物理性质是核结构理论重要的研究课题,相关理论计算可以为实验研究提供有益参考。主要介绍了该研究方向的基本理论框架,包括Tohsaki-Horiuchi-Schuck-Röpke波函数方法、Yamada-Schuck模型,以及近期提出的半解析近似方法。还讨论了α粒子间四体相互作用对α凝聚体物理性质的影响,并对α凝聚体破裂和一维α凝聚体等可能的研究方向做了简要论述。α condensates are exotic states in nuclear many-body systems, and can be viewed as the generalization of the Bose-Einstein condensate in nuclear physics. It is widely believed that, α condensates exist not only in 12C, but also in heavier self-conjugate nuclei such as 16O, 20Ne, 24Mg, 28Si, etc. It is important to understand the physical properties of these α condensates in heavy self-conjugate nuclei from the theoretical perspective, and the theoretical results could be a useful reference for the experimental studies. This work reviews the basic frameworks to study α condensates, including the Tohsaki-Horiuchi-Schuck-Röpke wave function, the Yamada-Schuck model, and the recently proposed semi-analytic approximation. The impacts of the four-body interactions of α particles on the physical properties of α condensates are reported. The breakup of α condensates and the one-dimensional α condensates are discussed briefly as the possible future directions in this field.     

奇Z超重核的禁戒α衰变(英文)

采用密度依赖的结团模型研究了奇Z 超重核的禁戒α衰变, 粒子与子核之间的微观核势通过双折叠模型对M3Y 核子-核子相互作用势以及 粒子与子核的密度积分给出。 粒子与子核之间的库仑相互作用也通过 粒子与子核的电荷密度积分给出。计算发现,由于非零角动量带来的禁戒效应和小的α粒子预形成几率,奇Z 超重核的α衰变寿命会明显变长。We investigate the α-transition of odd-Z superheavy nuclei by the density-dependent cluster model (DDCM). The microscopic nuclear potential between the -particle and the daughter nucleus is evaluated numerically from the double-folding model with the standard M3Y nucleon-nucleon interaction. The Coulomb potential is also obtained from the double-folding integral of the proton-proton Coulomb interaction with the charge density distributions of α-particle and daughter nucleus. From our calculations, enhanced stability againstα-decays is found for the odd-Z superheavy nuclei due to the hindrance effect of non-zero angular momentum and the small preformation factor of the -particle.     

原子核的大质量转移反应和丰中子超重核的产生(英文)

迄今为止,人们合成的超重核都是缺中子的,无论是熔合-裂变反应还是碎化过程都无法使产物达到周期表的“东北区域”。而重核之间(如U核之间) 的近垒大质量转移反应则可能是目前生成丰中子超重核和达到未知丰中子重核区域的唯一途径。在改进的量子分子动力学(ImQMD) 模型结合统计模型框架内,研究了U+U等反应体系的大质量转移反应,计算了反应产生的初生态碎片的质量和电荷分布,并成功再现了产物的终态质量和电荷分布。通过比较3 个反应136Xe+248Cm,48Ca+248Cm和238U+248Cm 产生的106号元素的截面大小,揭示了U+U等重核大质量转移反应对产生丰中子超重核是非常有利的。For elements with Z > 100 only neutron deficient isotopes have been synthesized so far. The “northeast area” of the nuclear map can be reached neither in fusion-fission reactions nor in fragmentation processes.The large mass transfer reactions in near barrier collisions of heavy (U-like) ions seem to be the only reaction mechanism allowing us to produce neutron rich heavy nuclei including those located at the superheavy(SH) island of stability and unexplored area of heavy neutron-rich nuclides. This study is extremely important for nuclear astrophysical investigations and, in particular, for the understanding of the r process. In this paper within the Improved Quantum Molecular Dynamics (ImQMD) model combining with the statistical-evaporation model, the large mass transfer reactions, like 238U+238U have been studied. The charge and mass distributions of transiently formed primary fragments are investigated within the ImQMD model and de-excitation processes of those primary fragments are described by the statistical decay model. The mass distribution of the final products in 238U+238U collisions is obtained and compared with the recent experimental data. Through compared the formation cross sections of transfermium element 106 by three reactions of 136Xe+248Cm, 48Ca+248Cm and 238U+248Cm, it is explored that the large mass transfer reactions, like U+U are very benefit for the production of SH nuclei.     

α-结团模型对超重核α衰变寿命的研究

用α-结团模型计算新合成超重元素的半衰期,与已知的实验数据进行对比分析,发现理论和实验数据能够很好地符合,验证了α-结团模型对超重核研究的有效性.同时结合标准的形变Hartree-Fock模型核质量表给出半衰期理论计算结果,可供以后在理论或实验上研究超重核参考,在此基础上进一步分析超重核区域的α衰变能、双中子分离能和双质子分离能,并讨论Z=114和N=184处是否存在壳效应.     

通过破裂反应研究轻丰中子核的集团结构

概括介绍了关于轻丰中子同位素链集团结构的理论模型和通过破裂反应研究该结构的实验方法、 实验装置及物理分析。 The theoretical models of the cluster structures of the light neutron rich nuclei as well as the corresponding physical mechanism and experimental approaches by breakup reaction have been introduced, which may serve as references for possible experimental studies of the cluster structure of light neutron rich nuclei.      

大型壳模型计算中的截断效应对132Sn附近丰中子空穴核能级结构的影响

以双幻核132Sn以及附近的空穴核131Sn,130Sn,131In,130In,130Cd为例,研究了大型壳模型计算中的截断效应对该核区能级结构以及电四极跃迁的影响,其中截断包括了有无中子跨壳激发,以及限制轨道粒子数两种情况。计算结果表明,只有在允许质子跨壳激发的情况下才能给出130In与实验相符的基态能级,而允许两个中子的跨壳激发则会改善132Sn的低激发能级结构。此外中子壳芯激发也会对该核区空穴核的低激发能级有一定的影响,相应低能态之间的电四极跃迁则更加敏感地反映出了空间截断效应的影响。With two different truncations, i.e., neutron core-excitation truncation and orbital particle-number truncation, the research is studied at the truncation effects in shell-model calculations by the hole nuclei of 130Sn, 131Sn, 130In, 130In and 130Cd. We found that the right ground state of 130In needs proton core-excitation in shell model space, and allowing two neutron core-excitations will promote the low-lying states in 132Sn. The neutron core-excitations will also slightly affect the low-lying levels of hole-nuclei close to 132Sn, and the values of BE2 between the corresponded low-lying states reflect more obviously to the neutron core-excitations.     

超重核性质的新观点(英文)

简单回顾了超重核的理论研究现状,讨论了形变对长寿命重核α衰变半衰期的影响。分析了相对论平均场模型的有效范围。强调了α衰变、结团放射性和自发裂变中应保持宇称守恒。提出了一些新观点。Status of theoretical studies on superheavy nuclei is simply reviewed.We investigate the influence of nuclear deformation on half lives of α decay forlong lifetime nuclei beyond 208Pb. The range of the validity of relativistic mean field model is analyzed and discussed. The conservation of parity in α decay, cluster radioactivity, and spontaneous fission of nuclei is stressed. New views on the properties of superheavy nuclei are presented.     

Exotic Isomers in Deformed Atomic Nuclei

Excited states of atomic nuclei can have long half lives, due to the angular-momentum couplings of unpaired nucleons. Such isomeric states provide opportunities for exploring novel nuclear physics, astrophysics and physics at the atomic/nuclear interface. This review focuses on the properties of isomers in deformed nuclei, and emphasises the importance of axial symmetry in preserving the integrity of the K quantum number. A region of neutron-rich nuclei around ¹⁸⁸Hf (Z=72, N=116) is predicted to have exceptional isomer properties, and experimental advances are now opening up this region to detailed investigation. This revised version was published online in July 2006 with corrections to the Cover Date.     

r-过程路径核β——衰变半衰期的估算

分析了20 < A < 190范围内丰中子核β衰变的实验数据,根据半衰期随质子数、中子数以及衰变能变化所呈现的壳效应和对效应等特点,提出了一种有效估算丰中子核β衰变寿命的公式。新的计算公式形式简单包含了较少的参数、计算量小。用该公式能较为准确地再现丰中子核的β衰变半衰期。用RIKEN最新测量丰中子核半衰期检验了该公式的外推能力,本工作可以为r-过程研究提供可靠的输入数据。Experimental data of the β--decay half-lives for the nuclei with atomic number between 20 and 190 are investigated. We have systematically studied the shell effects and pairing effects on β--decay half-lives versus the decay energy Q and nucleon numbers (Z, N). An empirical formula has been proposed to calculate the β--decay half-lives of neutron-rich nuclei. The empirical formula is simple and has relatively few parameters. Experimental β--decay half-lives of the neutron-rich nuclei are well reproduced by the new formula. In addition, the extrapolating capacity of this formula has been checked with the very recent experimental data from RIKEN. The predicted half-lives for r-process relevant nuclei with the current formula can be served as the reliable input of r-process model calculations.     

Neutron Halo and Nuclear Shell Structure in New Nuclide 31Ne

The ground state properties of new nuclide ^31Ne are investigated within the framework of the density-dependent relativistic mean-field theory.One-neutron halo in ^31Ne is predicted.Calculations also show that the ground state of ^31Ne is (3/2)^- and it can be used for the testing of the nuclear shell structure near the neutron-drip line.     

遗传算法研究原子团簇

遗传算法作为一种结构优化方法应用于研究原子团簇的结构和性质,具有高效和全局搜索等特点。本扼要介绍遗传算法基本特征、优化程序和方法。重点讨论我们近年来在应用遗传算法研究碳６０分子聚集超团簇的幻数,金团簇有序和无序结构,双金属团簇的偏析效应以及过渡金属团簇电磁性质的结构关联等方面所取得的一些结果,说明遗传算法与传统优化方法相比确具一定优势,以及需要解决的问题。     

理论预测超重核274-291Cn和266-287Ds的衰变模式

自发裂变和α衰变是影响超重核稳定性的两个主要因素。为了探索270Ds附近的长寿命的超重核,系统地计算了电荷数在104 ≤ Z ≤ 112范围内的α衰变与自发裂变之间的竞争。采用推广的液滴模型和唯象的解析公式计算了α衰变半衰期。基于包括壳效应和同位旋效应的WKB近似方法估算了相同超重核的自发裂变半衰期,进而预测了未知超重核274-276,279Cn与267-269Ds的衰变模式。The stability of superheavy nuclei (SHN) is controlled mainly by spontaneous fission and α decay processes. To investigate whether long lived SHN could really exist around 270Ds, the competition between α decay and spontaneous fission in the region 104 ≤ Z ≤ 112 are studied systematically. The α decay half-lives are investigated by employing a generalized liquid drop model (GLDM) and phenomenological analytical formula. Calculations of spontaneous fission half-lives for the same SHN are carried out based on the Wenzel-Kramers-Brillouin(WKB) approximation with both the shell effect and the isospin effect included. Decay modes are predicted for the unknown nuclei 274-276,279Cn and 267-269Ds.     

原子核中新的有效相互作用、新对称性及奇特核态

总结了近年来对奇特核和极端条件下核物质的研究结果,包括原子核的新有效相互作用、新对称性及奇特性质.在相对论平均场理论中,发现了反核子谱中的自旋对称性,提出了包含微观质心修正的新相互作用PK1,PK1r和PKDD?.这些新相互作用不但可以很好地描述核物质与中子星,还可以很好地给出靠近或远离β稳定线的原子核性质,包括中子滴线核与超核中的晕和巨晕现象.