锕系原子核自发裂变性质的理论研究

运用推广的液滴模型（GLDM）来确定锕系原子核的自发裂变势垒, 采用量子力学中的WKB近似方法对相应自发裂变的半衰期进行了研究。 在GLDM中, 首次考虑了微观Strutinsky壳修正对裂变势垒的影响。 理论计算的锕系区重核自发裂变半衰期与实验值符合得很好, 表明包括微观壳修正的GLDM可以成功研究重核的自发裂变性质。 The spontaneous fission half lives of the actinides are calculated by the WKB approximation and the potential barriers are constructed by a General Liquid Drop Model (GLDM) including the proximity energy, the mass and charge asymmetry, and an accurate nucleus radius. The microscopic shell correction which plays a key role for the spontaneous fission barrier is considered for the first time. The two parameter quasi molecular shape and the proximity are described in details within the GLDM. The effects of the microscopic shell correction and proximity energy for fission barrier are discussed separately. The calcula ted spontaneous fission half lives for the actinides reasonably accord with the experimental data, implying the present GLDM combined with the microscopic shell correction can be used to study the spontaneous fission properties of heavy nuclei successfully.     

推广的液滴模型及其应用

简单介绍了近年来在研究重核和超重核衰变性质及熔合反应方面取得的理论成果和面临的挑战,着重阐述推广的液滴模型(GLDM) 理论框架及其应用。基于原子核的质量数、质子数以及反应Q 值,GLDM考虑了质量和电荷的不对称性、形状演化、亲近势和温度等,很好地描述了重核和超重核的质子放射性、 衰变、重离子放射性、自发裂变的半衰期和重离子熔合反应截面,同时也研究了原子核的粒子(质子、 、重离子) 放射性与自发裂变的竞争。Recent theoretical achievements and challenges about the fusion and decay properties of heavy and superheavy nuclei are generally introduced. Especially, the Generalized Liquid Drop Model(GLDM) as well as its application are emphatically described. Based on the mass number, proton number and the reaction Q value, the GLDM has taken the mass and charge asymmetry, the shape evolution, the proximity potential, as well as the temperature of nucleus into account, well described the proton radioactivity, the decay, the heavy particle radioactivity, the half life of spontaneous fission of heavy nuclei and superheavy nuclei, and the cross-sections of heavy ion fusion. The competitions between the spontaneous fission and other decay modes such as proton and heavy particle radioactivity, the alpha decay, and so on are also studied.     

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.     

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.     

Structure and reaction dynamics of SHE Z = 130

This study investigates the structural properties of super-heavy nuclei with Z = 130 by adopting the relativistic mean-field(RMF) theory within an axially deformed oscillator basis with the NL3 force parameter set. We study the binding energies, quadrupole deformation, nuclear radii, neutron separation energies, and other bulk properties.Moreover, we analyze the favorable decay modes for clear cognitive content of nuclei, such as alpha decay, using different formulae including the Viola-Seaberg, analytical formula of Royer, universal curve formula, and universal decay law. We compare these with the corresponding fission process. The spontaneous fission of super-heavy nuclei is studied with Z = 130 within the mass region 310 ≤A≤340. The results exhibit good agreement with finite range droplet model(FRDM) data. This formalism presents a significant step forward in the study of the structure and decay modes of the isotopes of Z = 130. With this appraisal, we investigate the possible shell/sub-shell closure for super-heavy nuclei adjacent by decay chains of alpha and other radioactive decay particles.     

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.     

Alpha Decay,Shell Structure,and New Elements

We systematically analyze the experimental data of alpha decay in even-even heavy nuclei far from stability and find that the Geiger-Nuttall law brea~s for an isotopic chain when its neutron number is across a marc number or there is a deformed subshell. This break can be used to identify new magic numbers of superheavy nuclei. It is also discovered that there is a new linear relation between the logarithm of half-life and the reciprocal of the square root of decay energy for N = 126 and N = 152 isotones. It could be a new law of alpha decay for nuclei with magic neutron numbers but the physics behind it is to be explored. The significance of these researches for the search of new elements is discussed.     

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.     

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-lives 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 α 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 α 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.     

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.     

A systematic study of α-decay in superheavy nuclei using a Hartree-Fock-Bogoliubov model

Predictions on the alpha decay and spontaneous fission of the superheavy nuclei in the range of Z = 106–118 have been systematically done within the Hartree-Fock-Bogoliubov model and different Skyrme type interactions. A comparison of the results of the current study with experimental values showed good agreement. This study was extended to unknown isotopes in the range of Z = 116–118. The calculated alpha decay half-lives are in the range of ${10}^{-5}$ to 10² s which lie within measurable values. To identify the long-lived isotopes in the mass region, spontaneous fission half-lives were performed using a semi-empirical formula. The results revealed that the isotopes ^{276,275,274,272,268}110, ^276,275,273111, ^282,280,279112, ^281,280,279113, ^284,283114, ²⁸⁶115, ²⁸⁹116, ^{296,295,292,291}117, ^297,296118, and ^295,293,292118 survived fission and had alpha decay mode as the predominant mode of decay which could be synthesized in the laboratory.     

Synthesis of superheavy nuclei in 48Ca+244Pu interactions

This article reports the results of experiments aimed at producing hypothetical long-lived superheavy elements located near the spherical-shell closures with Z≥114 and N≥72. For the synthesis of superheavy nuclei, we used a combination of neutron-rich reaction partners, with a ²⁴⁴Pu target and a ⁴⁸Ca projectile. The sensitivity of the present experiment exceeded by more than two orders of magnitude previous attempts at synthesizing superheavy nuclides in reactions of ⁴⁸Ca projectiles with actinide targets. We observed new decay sequences of genetically linked alpha decays terminated by spontaneous fission. The high measured alpha-particle energies, together with the long decay times and spontaneous fission terminating the chains, offer evidence for the decay of nuclei with high atomic numbers. The decay properties of the synthesized nuclei are consistent with the consecutive alpha decays originating from the parent nuclides ^288,289114, produced in the 3n-and 4n-evaporation channels with cross sections of about a picobarn. The present observations can be considered experimental evidence for the existence of the “island of stability” of superheavy elements and are discussed in terms of modern theoretical approaches.     

Proton radioactivity within the generalized liquid drop model with various versions of proximity potentials

In the present work, we systematically investigate the proton radioactivity half-lives of spherical proton emitters adopting a generalized liquid drop model(GLDM) with 16 different proximity potentials, of which the proximity potential Prox.77-13 gives the closest results to the experimental data. Combined with the previous conclusion that the GLDM with proximity potential Prox.77-13 can also best describe α decay half-lives, which makes the model more uniform and consistent.Further, we use the proximity potential Prox.77-13 in GLDM to predict the proton radioactivity half-lives of 14 spherical proton emitters that are allowed energetically but not yet observed experimentally or specifically quantified. Finally, we research the Geiger-Nuttall law for proton radioactivity. The results reveal that the Geiger-Nuttall law can also be well used to study the proton radioactivity half-lives of isotopes with the same orbital angular momentum l.     

Heavy and superheavy nuclei

The new elements 110, 111 and 112 were synthesized and unambiguously identified in experiments at SHIP. Due to strong shell effects the dominant decay mode is not fission, but emission of alpha particles. Theoretical investigations predict that maximum shell effects should exist in nuclei near proton number 114 and neutron number 184. Our measurements give hope that isotopes of element 114 close to the island of spherical Superheavy Elements could be produced by fusion reactions using ²⁰⁸Pb as target. Systematic studies of the reaction cross-sections indicate that transfer of nucleons is the important process to initiate the fusion.     

Spontaneous Fission Barriers Based on a Generalized Liquid Drop Model

The barrier against the spontaneous fission has been determined within the Generalized Liquid Drop Model （GLDM） including the mass and charge asymmetry, and the proximity energy. The shell correction of the spherical parent nucleus is calculated by using the Strutinsky method, and the empirical shape-dependent shell correction is 6mp10yed during the deformation process. A quasi-molecular shape sequence has been defined to describe the whole process from one-body shape to two-body shape system, and a two-touching-ellipsoid is adopted when the superdeformed one-body system reaches the rupture point. On these bases the spontaneous fission barriers are systematically studied for nuclei from 2a~Th to 249 Cm for different possible exiting channels with the different mass and charge asymmetries. The double, and triple bumps are found in the fission potential energy in this region, which roughly agree with the experimental results. It is found that at around Sn-like fragment the outer fission barriers are lower, while the partner of the Sn-like fragment is in the range near l~SRu where the ground-state mass is lowered by allowing axially symmetric shapes. The preferable fission channels are distinctly pronounced, which should be corresponding to the fragment mass distributions.