Half-Lives of Superheavy Nuclei in Z=113 Alpha Decay Chain

The generalized liquid drop model （GLDM）, including the proximity effects and centrifugal potential, and the cluster model with Cosh potential are used to study the half-lives of some Z = 113 isotopes and their α-decay products. The experimental half-lives of 284^113, 283^113, 282^113 and their α-decay products are well reproduced by the two models when zero angular momenta transfer is assumed. For 278^113 and its α-decay products, both the GLDM and the duster model could provide satisfactory results if we assume the α particle carry five units of angular momenta, which indicates that possible nonzero angular momenta transfer and need further experimental measurements with high precision. Finally, we show that half-lives of α-decay are quite sensitive to the angular momentum transfers, and a formula could be used to describe the correlation between α-decay half-life and angular momentum transfer successfully.     

Systematic Study on Alpha Decay Half-Lives of Superheavy Nuclei

The α-decay half-lives of a set of superheavy nuclear isotope chain from Z = 105 to 120 have been analyzed systematically within the WKB method, and some nuclear structure features are found. The decay barriers have been determined in the quasi-molecular shape path within the Generalized Liquid Drop Model （GLDM） including the proximity effects between nucleons in a neck and the mass and charge asymmetry. The results are in reasonable agreement with the published experimental data for the alpha decay half-llves of isotopes of charge 112, 114, and 116, of the element 294118 and of some decay products. A comparison of present calculations with the results by the DDM3Y effective interaction and by the Viola-Seaborg-Sobiczewski （VSS） formulae is also made. The experimental a decay half lives all stand in between the GLDM calculations and VSS formula results. This demonstrates the possibility of these models to provide reasonable estimates for the half-lives of nuclear decays by a emissions for the domain of SHN. The half-lives of these new nuclei are thus well tested from the reasonable consistence of the macroscopic, the microscopic, the empirical formulae and the experimental data. This also shows that the present data of SHN themselves are consistent. It could suggest that the present experimental claims on the existence of new elements Z =110 - 118 are reliable. It is expected that greater deviations of a few SHN between the data and the model may be eliminated by further improvements on the precision of the measurements.     

Atomic Processes Accompanying Alpha Decay of Superheavy Nuclei

Physics of Atomic Nuclei - Processes involving the ionization of atomic shells and x-ray transitions in daughter nuclei and accompanying alpha decay of superheavy isotopes are considered. The...     

Alpha Decay as a Probe of the Structure of Neutron-deficient Nuclei Around Z =82

In this contribution I would like to review briefly our recent studies on nuclear α formation probabilities in heavy nuclei and their indication on the underlying structure of the nuclei involved. In particular, I will show that the empirical α-formation probabilities, which can be extracted from experimental half-lives, exhibit a rather smooth function with changing proton or neutron numbers. This allows us to distinguish the role played by pairing collectivity in the clustering process. The sudden hindrance of the clustering of the nucleons around the N = 126 shell closure is due to the fact that the configuration space does not allow a proper manifestation of the pairing collectivity. The influence of the Z = 82 shell closure on the α formation properties will also be discussed. Moreover, we have evaluated the α-decay fine structure to excited 0+ states in Hg and Rn isotopes as well as the α-decay from the excited 0+ states in the mother nucleus. It is thus found that the α decay is sensitive to the mixture of configurations corresponding to different nuclear shapes.     

N=Z原子核性质的研究

论述了N=Z核实验和理论研究的历史和现状在,N=Z,是研究T=0对关联最好的核区,实验表明T=0和n-p对关联起着重要的作用,理论研究知心朋友同时包括T=0和T=1的对关联,是研究它们之间竞争及相变。 The history and current status of the study of N=Z nuclei are reviewed. T=0 n p pairing correlation is expected to play an important role in the structure of the nuclei along N=Z line. Both T=0 and T=1 pairing modes should be included in the theoretical models. Phenomena like possible competition and phase transition between different pairing modes are becoming important issues in nuclear structure.     

丰中子轻核新幻数N=16的解释(英文)

基于中子分离能的分析 ,Ozawa等提出丰中子轻核存在新幻数 N=1 6.对 N=1 6同中子素进行了形变和球形的相对论平均场计算 .相对论平均场的数值结果表明N=1 6同中子素有形状相变.这是一些丰中子核新幻数出现的可能原因. Based on the analysis of neutron-separation energies, Ozawa et al proposed a new magic number N =16 in light neutron-rich nuclei. The deformed and spherical relativistic mean-field(RMF) calculations have been carried out for N =16 isotones. The numerical relativistic mean-field results show there is a shape transition in N =16 isotones. This is the possible cause of the appearance of the new magic number in someneutron-rich nuclei.     

Semiempirical Shell Model Masses with Magic Proton Number Z=126 for Translead Elements

A highly extrapolatable semiempirical shell model mass equation applicable to translead elements up to Z=126 is presented. The equation is applied to the recently discovered superheavy nuclei ²⁹³118 and ²⁸⁹114 and their decay products. This revised version was published online in July 2006 with corrections to the Cover Date.     

L-Shell Ionization during the Alpha Decay of Superheavy Nuclei from 117 294 Ts Tennessine Decay Chain and the Alpha Decay of the Polonium Isotope 84 210 Po

Physics of Atomic Nuclei - The probabilities for L-shell ionization following the alpha decay of 117 294 Ts, 113 286 Nh, 109 278 Mt, and 105 270 Db superheavy nuclei from the decay chain of...     

Neutron Drip Line for Nuclei in the Vicinity of the Neutron Magic Number N = 184

Ground-state properties of even-even nuclei were calculated over a broad region of mass numbers, including nuclei that contain a neutron excess in the vicinity of the neutron drip line. The calculation of the properties of such nuclei relied on the method of the relativistic and the nonrelativistic mean field and took into account the axial deformation of nuclei. Particular attention was given to nuclei beyond the theoretical neutron drip line, which form a peninsula of nuclei in the (N, Z) space at N = 184 that are stable against the emission of one or two neutrons.

     

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.     

Probable Decay Modes at Limits of Nuclear Stability of the Superheavy Nuclei

The modes of decay for the even–even isotopes of superheavy nuclei of Z = 118 and 120 with neutron number 160 ≤ N ≤ 204 are investigated in the framework of the axially deformed relativistic mean field model. The asymmetry parameter η and the relative neutron–proton asymmetry of the surface to the center (R _η ) are estimated from the ground state density distributions of the nucleus. We analyze the resulting asymmetry parameter η and the relative neutron–proton asymmetry R _η of the density play a crucial role in the mode(s) of decay and its half-life. Moreover, the excess neutron richness on the surface, facets a superheavy nucleus for β^? decays.     

Decay Mechanism of 290,292114* Superheavy Nuclei Formed in 48Ca-Induced Reactions

We calculate the neutron-evaporation residue cross sections σ _3n , σ _4n , and σ _5n in the hot-fusion reactions ⁴⁸Ca+^242,244Pu →^290,292114 ^? over a wide range of compound-nucleus excitation energies ( $E_{\text{CN}}^{*}$ = 34–53 MeV). We work with the dynamical cluster-decay model (DCM), with a single parameter, the neck-length parameter ΔR. To calculate neutron-evaporation cross sections, we choose the superheavy proton magic Z = 126 and neutron magic N = 184. Among the 3n, 4n, and 5n production cross sections for ^{290, 292}114^?, only the 3n decay cross sections of ²⁹²114^? correspond to spherical fragmentation. The 4n and 5n cross sections of ²⁹²114^? and 3n, 4n, and 5n cross sections of ²⁹⁰114^? could only be fitted after the inclusion of quadrupole deformations β _2i within the optimum orientation approach. Changes in the angular momentum and N/Z ratio do not significantly influence the fragmentation paths of ^{290, 292}114^? superheavy nuclei. Larger barrier modification is required for the lower angular momentum states and lighter neutron clusters. The contribution of the fusion–fission component is also computed for the compound nucleus ²⁹²114^? in the energy range $E_{\text{CN}}^{*}$ = 27–47 MeV.     

Mass Measurements of Exotic Nuclei around N=Z=40 with CSS2

Mass measurements of the N=Z nuclei ⁸⁰Zr, ⁷⁶Sr, ⁶⁸Se were performed for the first time and a new measurement was obtained for ⁸⁰Y, using the second cyclotron CSS2 of GANIL as a high-resolution spectrometer. Ions around N=Z were produced by fusion-evaporation in the inverse ⁵⁸Ni (4.32MeVA) + ²⁴Mg and ¹²C reactions. New masses were measured by a time-of-flight method, with a precision of 2⋅10⁻⁶, by using well-known masses as references. Study of the double binding energy difference δV _np is then performed leading to a strong N=Z Wigner effect around N=Z=40. Knowledge of new masses in this region also plays a crucial role in the modelling of the astrophysical rp process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Shell Evolution Study for New Magic Number N =32 via Isochronous Mass Spectrometry

Recent results and progress of mass measurements of neutron-rich nuclei utilizing Isochronous Mass Spectrometry (IMS) based on the HIRFL-CSR complex at Lanzhou are reported. The nuclei of interest were produced through projectile fragmentation of primary 86Kr ions at a realistic energy of 460.65 MeV/u. After in-flight separation by the fragment separator RIBLL2, the fragments were injected and stored in the experimental storage ring CSRe, and their masses were determined from measurements of their revolution times. The re-determined masses were compared and evaluated with other mass measurements, and the impact of these evaluated masses on the shell evolution study is discussed.     

基于双核模型对Z = 116~ 121 超重核产生截面的研究(英文)

在双核模型的理论框架下系统研究了超重元素Z = 116 ~121 的蒸发剩余截面,计算过程中核子扩散由主方程描述,同时考虑了全熔合与准裂变的竞争。计算基本再现了利用热熔合反应48Ca+245Cm,48Ca+249Cf 和48Ca+249Bk 产生116~118 号同位素的合成截面。同样,分别以249Bk,249Cf 和243Am 为靶,以48Ca,50Ti 和58Fe 为炮弹,计算了Z = 119~ 121 号同位素的生成截面。结果表明,这些超重核的生成截面随着质子数的增大进一步变小。例如,利用58Fe+243Am 反应合成121 号同位素的最大蒸发剩余截面仅在fb 量级。基于对选择的几个反应系统的系统分析,发现双核系统在熔合蒸发过程中偶Z 奇N 和奇Z 偶N 复合核分别有强的3n 和4n 蒸发道。The production cross sections of superheavy elements with Z = 116~121 have been investigated systematically within the dinuclear system (DNS) concept, where the master equation is solved numerically to obtain the fusion probability. The competition between complete fusion and quasifission, which can strongly affect the cross section of the compound nucleus formation, is taken into account. The evaporation residue cross sections ER calculated for the hot fusion actinide-based reactions (48Ca+245Cm, 48Ca+249Cf and 48Ca+249Bk) are basically in agreement with the known experimental data within one order of magnitude. Similar calculations for the synthesis of superheavy elements up to Z = 121 are performed using the available 249Bk, 249Cf and 243Am as targets and 48Ca, 50Ti and 58Fe as projectiles. Their production cross sections are relatively small,especially for the 58Fe+243Am→301121 reaction. A systematic analysis indicates that the 3n and 4n channelsare respectively the most favorable fusion-evaporation channels in the synthesis of even- and odd-Z superheavy elements.     

Decay properties of isomeric states in radium isotopes close to N = 126

Isomeric states in ^210-215Ra have been populated by the decay of the compound nuclei ^216,220Ra produced in irradiations of ^204,208Pb with ¹²C at MeV. Published values for -ray energies and half-lives were confirmed for Ra. Our data for Ra agree with the -energies and the half-life measured at the RITU separator, University of Jyväskylä (Finland). Its decay pattern is complex. Two series of -rays of keV and keV were observed. A half-life of s was measured. The isomeric state is attributed to an 8 ⁺ state at E ^* = 2053.8keV. A previously unknown isomeric state was assigned to Ra. It has a half-life of ( ) and it decays by emission of -rays with energies of 396.1keV and 802.0keV. It is attributed to a 13/2 ⁺ state at E ^* = 1198.1 keV.PACS: 23.60. + e decay - 27.90. + b      

超重核性质与合成机制的理论研究

探索原子核的电荷与质量极限,合成长寿命超重核是当前原子核物理研究的重要前沿问题之一。本文综述了我们近几年在超重原子核结构性质与合成机制方面取得的理论研究进展。在结构性质方面,利用处理对关联的粒子数守恒方法,基于推转壳模型,系统研究了锕系核与超镄核低激发谱,发展了多维形状约束的协变密度泛函理论并用于研究锕系核势能面和裂变位垒以及N=150同中子素中的非轴对称八极关联等。在超重核合成机制方面,系统研究了利用重离子熔合反应合成超重核的三步过程,包括俘获过程——提出了一个位垒穿透概率新公式、熔合过程——提出了一个基于动力学形变势能面的双核模型、存活过程——系统研究了激发态超重复合核存活概率等。系统研究了合成超重核的热熔合反应,得到的熔合蒸发截面与实验符合,并预言了合成119和120号超重元素的生成截面。     

Theoretical Study on N = 126 Shell Evolution

The nuclei around magic number N = 126 are investigated in the deformed relativistic mean field (RMF) model with effective interactions TMA. We focus investigations on the N = 126 isotonic chain. The N = 126 shell evolution is studied by analyzing the variations of two-neutron (proton) separation energies, quadruple deformations, single particle levels etc. The good agreement of two-neutron separation energies between experimental data and calculated values is reached. The RMF theory predicts that the sizes of N = 126 shell become smaller and smaller with the increasing of proton number Z. However, the N = 126 shell exists in our calculated region all along. According to the calculated two-proton separation energies, the RMF theory suggests ²²⁰Pu is a two-proton drip-line nucleus in the N = 126 isotonic chain.     

Theoretical Study on N = 126 Shell Evolution

The nuclei around magic number N = 126 are investigated in the deformed relativistic mean field （RMF） model with effective interactions TMA. We focus investigations on the N = 126 isotonic chain. The N = 126 shell evolution is studied by analyzing the variations of two-neutron （proton） separation energies, quadruple deformations, single particle levels etc. The good agreement of two-neutron separation energies between experimental data and calculated values is reached. The RMF theory predicts that the sizes of N = 126 shell become smaller and smaller with the increasing of proton number Z. However, the N = 126 shell exists in our calculated region all along. According to the calculated two-proton separation energies, the RMF theory suggests ^220Pu is a two-proton drip-line nucleus in the N = 126 isotonic chain.