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.     

超重核α衰变寿命的理论研究

建立了计算球形核α衰变寿命的新模型——密度依赖的结团模型(DDCM)。在此基础上,通过引入子核的形变自由度,发展了形变的密度依赖的结团模型, 编写了形变的DDCM程序。并系统计算了Z=106—110的超重核α衰变寿命。通过与已有的实验数据的对比分析, 发现理论结果和实验数据符合得很好,验证了DDCM在超重核区域的适用性。We proposed a deformed version of density dependent cluster model (DDCM) by including nuclear deformation of the daughter nucleus. A systematic calculation of α decay half lives of superheavy nuclei (Z=106—110) is carried out by the deformed DDCM. The good agreement between theory and data is obtained. It is shown that the deformed DDCM works well in the superheavy mass region.     

α结团模型在形变核区域的推广

将α结团模型推广至形变核,计算偶偶形变母核α衰变基态到子核基态和子核第一激发态的分支比,显示出α衰变精细结构的测量是提取核形变信息的有效手段.The cluster model of α-decay is extended to deformed nuclei. The branching ratios of α-decays from the ground state of a parent nucleus to the ground state 0~(+) of its deformed daughter nucleus and to the first excited state 2~(+) are calculated in the framework of the cluster model. The results indicate that a measurement of α spectroscopy is a feasible method to extract the information of nuclear deformation.     

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.     

原子核放射性对核对称能的约束（英文）

核对称能的密度依赖性对于原子核物理和天体物理中的许多问题很重要。基于密度依赖的结团模型,奇特的结团放射性被用来约束核对称能及其斜率的大小。在密度依赖的结团模型中,清楚地给出了结团放射性子核208Pb的中子皮大小与对称能的斜率参数L（ρ0） 之间的关联。发现从M3Y核子-核子相互作用得到的结团-208Pb 同位旋矢量势对于对称能的斜率参数L（ρ0） 非常重要。基于结团放射性实验数据和新的208Pb 的中子皮大小实验数据,成功得到对称能的斜率参数L（ρ0） 的大小。也讨论了利用质子放射性数据提取的斜率参数L（ρ0）。The density-dependence of symmetry energy is of particular importance to many problems in nuclear physics and astrophysics. Exotic cluster radioactivity is proposed to constrain the density slope of symmetry energy L(ρ0) by using the density-dependent cluster model (DDCM) where the cluster radioactivity serves as a link between the neutron skin thickness of 208Pb and the density slope L(ρ0). The isovector part of cluster-208Pb potential constructed from the M3Y nucleon-nucleon interaction is found to be very important in determining the density slope parameter L(ρ0). The correlation between the neutron skin thickness of 208Pb and the density slope parameter are obtained from cluster radioactivities around 208Pb with measured data. The constraint of L(ρ0) from proton radioactivity is also discussed.     

基于折叠势的两势方法系统研究质子放射性(英文)

基于两势方法系统地研究了质子数51 ≤ Z ≤ 83质子放射性核素的衰变半衰期。总的质子-子核相互作用势包括:通过单折叠子核密度和DDM3Y有效相互作用得到的微观核势,通过单折叠子核电荷密度和质子-质子库仑相互作用得到的真实库仑势以及离心势。同时,预测了同一区域16个核的质子放射性半衰期,并且预测的质子放射性半衰期在4.11倍的范围内。此外,还研究了质子放射性的Geiger-Nuttall定律。结果表明,Geiger-Nuttall定律可以用来描述角动量相同的同位素的质子放射性。In the present work, we systematically study the half-lives of proton radioactivity for 51 ≤ Z ≤ 83 nuclei within the two-potential approach. The total emitted proton-daughter nucleus interaction potential is composed of the microscopic nuclear potential obtained by single folding the density of the daughter nucleus with the DDM3Y effective interaction, the realistic Coulomb potential obtained by single folding the charge density of the daughter nucleus with the proton-proton Coulomb interaction and the centrifugal potential. We extend our study to predict proton radioactivity half-lives of 16 nuclei in the same region within a factor of 4.11. In addition, the Geiger-Nuttall law for proton radioactivity is researched. The results indicate that the Geiger-Nuttall law can be used to describe the proton radioactivity isotopes with same angular momentum.     

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.     

核物质中△(1 232)粒子的介质效应

利用手征有效场论, 通过对核物质中核子传播子的修正, 研究了核物质中的△(1 232)粒子的有效质量和衰变宽度。 发现△(1 232)粒子的有效质量随核物质密度的增加而减小, 而衰变宽度随核物质密度的增加而增加; △(1 232)粒子衰变宽度的变化主要取决于核子有效质量以及△(1 232)粒子有效质量的变化。 Based on the chiral effective field theory (CHEFT), we study the effective mass and decay width of △(1 232) in the nuclear matter with the modified nucleon propagator. We find that the effective mass of △(1 232) decreases, while the decay width of △(1 232) increases with increasing the density of nuclear matter. And the decay width of △(1 232) mainly depends on the effective masses of nucleon and △(1 232)     

Generalization of α-Decay Cluster-Model to Nuclei Near Spherical and Deformed Shell Closures

The cluster model of α-decay is extended to the regions around doubly magic spherical nucleus 208pb and around deformed shell closure 270Hs, respectively. The effects of spherical shell closures (N = 126 and Z = 82) on α-decay are investigated by introducing an N-dependent α-preformation factor and a Z-dependent one inspired by a microscopic model. Good agreement between the theoretical α-decay half-lives and the measured ones is obtained for the spherical nuclei near the doubly magic nucleus 208 Pb, where the nuclear shell effect is included in the expression of α-preformation factor. The cluster model is also generalized for the decay of deformed nuclei. The branching ratios of a-decays from the ground state of a parent nucleus to the ground state (0 ) of its deformed daughter nucleus and to the first excited state (2 ) are .calculated in the framework of the cluster model. The results indicate that a measurement of c spectroscopy is a feasible method to extract the information of nuclear deformation of superheavy nuclei around the deformed nucleus 270 Hs.     

Critical behavior of a dynamical percolation model

The critical behavior of the dynamical percolation model,which realizes the molecular-aggregation conception and describes the crossover between the hadronic phase and the partonic phase,is studied in detail. The critical percolation distance for this model is obtained by using the probability P∞ of the appearance of an infinite cluster. Utilizing the finite-size scaling method the critical exponents γ/ν and τ are extracted from the distribution of the average cluster size and cluster number density. The influences of two model related factors,i.e. the maximum bond number and the definition of the infinite cluster,on the critical behavior are found to be small.     

Microscopic theory of cluster radioactivity

Recent developments in the dynamical microscopic theories of cluster decay are reviewed with special emphasis on the nuclear structure aspects and physical interpretation of the models. What we call dynamical microscopic theories are those in which the decay width is derived from the nucleonic structures, of the participating nuclei, which are deduced through the solution of their equations of motion. After a brief review of the various expressions for the decay width, we turn to the nuclear-structure aspects of the problem. We thoroughly discuss the treatment of the Pauli effects in models involving macroscopic elements. We settle the long-standing controversy over the cluster-core norm operator that relates microscopic and macroscopic relative-motion wave functions in the transition amplitude. We conclude that the way the norm operator was originally introduced in the mid-1970s is in principle correct. The main part of the paper is a detailed review, in which the approaches considered are categorized according to the structure models used for the parent nucleus. The approaches discussed are the ordinary shell models, the cluster-like shell models and the Bardeen-Cooper-Schrieffer (BCS) approach. By discussing these diverse calculations, it is concluded that the most essential prerequisite for a realistic model of the mother nucleus is that it should correctly describe the cluster correlation in the surface region. This implies that the proton-neutron interaction is indispensable, and the moderate success of ordinary shell models is accounted for by their failure to include both proton-neutron interaction and large enough bases. For the special case of a doubly-closed-shell residual state, cluster-like models are able to cope with this problem, because their bases are more economical, and, for these cases, they provide a fully satisfactory decay theory. The BCS approach, on the other hand, is widely applicable, and is the only one that has been applied to heavy-cluster decay with reasonable success. We point out, however, that the formation amplitude calculated in this model still contains approximations. We explain the success of the BCS theory by showing that, in spite of appearance, it does include proton-neutron interaction, in an effective manner. In discussing the results for the widths, we address the problem of the preformation probability of a cluster-core pair in the parent nucleus. One can be fairly confident that in the ground state of ²¹²Po the amount of core-α-clustering is as high as 20–30%, but, in respect of other cluster-decaying nuclei, the theory is not yet conclusive. We conclude that a satisfactory understanding of heavy-cluster radioactivity requires the application of both more sophisticated cluster models and improved BCS approaches.     

Role of the cluster deformations in explaining the exotic decay half-lives

We investigate the influence of nuclear deformations of the cluster and daughter nuclei on the exotic cluster decay half-lives of $\ensuremath 221\leq A \leq 242$ for the favored cluster decay of the radioactive nuclei by using the semiclassical WKB method and the Bohr-Sommerfeld quantization condition. The results have also been presented for the spherical nuclei case in order to show clearly the effects of the deformations on the exotic decay half-lives. The half-lives become close to the experimental data when both the deformation of daughter and cluster nuclei are taken into account in the calculations. Furthermore, considering cluster deformations together with the orientation angles of daughter and cluster also provides positive contributions to the results.     

Systematic studies on α-decay half-lives for super heavy nuclei

Radioactive decay of super heavy nuclei via the emission of α-particles has been studied theoretically in the preformed cluster model (PCM). The nucleus-nucleus (NN) potential is obtained by double folding the density distributions of the α-particle and the daughter nucleus with a realistic effective interaction. The M3Y effective interaction, supplemented by a zero-range pseudo-potential for exchange term, is used to calculate the NN potential. The α decay half-lives for 317 nuclei at Z=102–120 are performed in the PCM framework with the theoretical Q values extracted from the Mller-Nix-Kratz and Liran-Marinov-Zeldes mass tables and are compared with the experimental data. The calculated results are also compared with those obtained by using Q values from the Muntian-Hofmann-Patyk-Sobiczewski and Myers-Swiatecki mass estimates.     

Calculation of decay half-lives for superheavy elements using the double folding model

α decay half-lives of some new synthesized superheavy elements, possibly synthesized superheavy elements and decay products are calculated theoretically within the WKB approximation by using microscopic m-nucleus interaction potentials. These nuclear potentials between the α particle and daughter nuclei are obtained by using the double folding integral of the matter density distribution of the α particle and daughter nuclei with a density-dependent effective nucleon-nucleon interaction, in which the zero-range exchange term is supplemented. The calculated α decay half-lives are compared with those of the different models and experimental data. It is shown that the present calculation successfully provides the half-lives of the observed αdecays for some new superheavy elements and therefore gives reliable predictions for α decay of possibly synthesized superheavy elements in future experiments.     

Alpha-decay fine structures of U isotopes and systematics for isotopic chains of Po and Rn

A model of the cluster radioactivity of even-even nuclei is presented. In this model, the zero-point vibrations in the charge-asymmetry coordinate determine the cluster formation (spectroscopic factor), while the tunneling in the coordinate of the relative separation of the centers of mass of the cluster and the daughter nucleus determines the penetrability of the barrier of the nucleus-nucleus potential. The quality of the model is demonstrated for describing cluster decay half-lives and the fine structure in alpha decays of even-even U isotopes. The model is applied to describe the alpha decays in the isotopic chains of Po, Rn, and U. The correspondence of the calculated half-lives to the Geiger-Nuttall law is discussed.     

On a new mechanism of excitation of the absolute parametric decay instability of an electromagnetic wave in experiments on electron cyclotron resonance heating in toroidal devices

Experimental conditions under which the low-threshold absolute parametric decay instability of an electromagnetic wave with extraordinary polarization at the electron cyclotron resonance heating of a plasma at the second harmonic resonance in toroidal devices are analyzed. A new mechanism is proposed for the localization of a daughter electrostatic wave in the toroidal direction in the region of a high-power pump beam. This mechanism, along with the two-dimensional localization of the daughter wave because of a nonmonotonic radial profile of the plasma density and the poloidal inhomogeneity of the magnetic field, can be responsible for the parametric excitation of a three-dimensional cavity for this wave and, as a result, low-threshold absolute decay instability of the pump wave.     

Nuclear Energy Density Functional and the Nuclear α Decay

We study the nuclear α decay of heavy nuclei using nuclear energy density functionals. This allows us to write the structure of the nuclear α potential inside the parent nucleus in terms of the proton and neutron density profile of the daughter nucleus with ad hoc parameters which control the strength of the potential. We adopt the Skyrme force model, Gogny force model, and relativistic mean field model to get the nucleon density profiles inside heavy nuclei. This approach is then applied to get predictions for unknown decay halflives of heavy nuclei and our results are compared with other model predictions.     

Spectroscopic factors within the dinuclear-system model

A model of the cluster radioactivity of even—even nuclei is presented. In this model, zero-point vibrations in the charge-asymmetry coordinate determine spectroscopic factors, while tunneling in the coordinate of the relative separation of the centers of mass of the cluster and the daughter nucleus determine the penetrability of the barrier of the nucleus-nucleus potential. The conservation of the total spin and energy in the decay process is taken into account. The potential of the model for describing experimental half-lives is demonstrated. A number of predictions for possible cluster-emission reactions in the regions of lead and tin radioactivities are made.