Superheavy nuclei in deformed mean--field calculations

The ground–state properties of superheavy nuclei are investigated within various parametrisations of relativistic and nonrelativistic nuclear mean–field models. The heaviest known even–even nuclei starting with Z = 98 are used as a benchmark to estimate the predictive power of the models and forces. From that starting point, deformed doubly magic nuclei are searched in the region 100 ≤ Z ≤ 130 and 142 ≤ N ≤ 190. Received: 6 April 1998 / Revised version: 16 June 1998     

Systematics of spontaneous-fission barrier heights

Heights of (static) spontaneous-fission barriers of heaviest nuclei are calculated within a macroscopic—microscopic approach. Even—even nuclei with proton numbers Z = 96–120 are considered.     

Shell energy in the heaviest nuclei using the Green’s function oscillator expansion method

The Greens function oscillator expansion method and the generalized Strutinsky smoothing procedure are applied to shell corrections in the heaviest elements. A macroscopic-microscopic method with a finite deformed Woods-Saxon potential is used. The stability condition for the shell correction is discussed in detail and the parameters defining the smoothing procedure are carefully determined. It is demonstrated that the spurious contribution to the total binding energy due to the unphysical particle gas that appears in the standard method can be as large as 1.5 MeV for weakly bound neutron-rich superheavy nuclei, but the effect on energy differences (e.g., alpha-decay values) is fairly small.     

Nuclear structure in the vicinity of the N = Z line in the A = 90-100 region

Neutron-deficient nuclei in the mass region A≈ 90-100 exhibit a large variety of phenomena. In this region the heaviest N = Z nuclei are identified and enhanced neutron-proton correlations are expected when protons and neutrons occupy identical orbitals. A variety of nuclear shapes are predicted and observed for A? 91, including superdeformed shapes. The nucleus ¹⁰⁰Sn is the heaviest N = Z doubly magic nucleus believed to be bound. Knowledge of the shell structure around ¹⁰⁰Sn is of utmost importance for understanding the nuclear shell model. New results on both the N = Z nucleus ⁸⁸Ru, superdeformed structures in A≈ 90 nuclei as well as the first result on the level structure in ¹⁰³Sn, and an extended level structure in ¹⁰²In are presented. The limitations of using stable beams and targets and the possibilities with new radioactive beams are briefly outlined. Received: 1 May 2001 / Accepted: 4 December 2001     

超重核密度的计算

用Skyrme Hartree Fock模型计算了超重核的密度分布,并讨论了其形状和同位旋相关性。 以292120核为例,计算表明形变对密度分布有相当大的影响。     

Superheavy nuclei in self-consistent models

The shell structure of superheavy nuclei is investigated within various parametrizations of relativistic and nonrelativistic nuclear mean-field models. The heaviest known even-even nuclei are used as a benchmark to estimate the predictive value of the models. From that starting point, spherical and deformed shell closures in the superheavy region are searched.     

Production cross sections for the heaviest nuclei in complete fusion reactions induced by heavy ions

Production of the heaviest nuclei in complete fusion reactions induced by heavy ions has been considered in a systematic way in the framework of the conventional barrier passing model coupled with the statistical model. Available data on excitation functions for fission and production of evaporation residues (ER) in very asymmetric combinations induced by ions lighter than Ne on actinide target nuclei are described rather well in the framework of these models. The data allow one to adjust model parameters and to reveal the quasi-fission effect caused by the interaction with deformed target nuclei, which is manifested in the suppression of the ER production at sub-barrier energies. For reactions induced by Mg and heavier projectiles, quasi-fission is starting to suppress fusion (ER production) at energies above the Coulomb barrier. One has to introduce empirically the quantity of the fusion probability P_fus to reproduce the ER excitation functions in the framework of the conventional approach. The exponential dependence of P_fus on the combined fissility parameter (a similar parameter that was introduced for the extra-push energy scaling) was found in search for scaling for the P_fus values resulting from the data analysis.     

Superheavy nuclei in the RMF framework

The structure of superheavy even even nuclei is investigated using the self-consistent axially-deformed relativistic mean-field model (RMF) with BCS pairing. The isovector properties of the standard RMF ansatz are studied and the new RMF parameterization is tested with a better account for nuclei away of the line of stability. The heaviest even even nuclei are used as a benchmark to estimate the predictive power of the model.     

Fusion cross sections for superheavy nuclei in the dinuclear system concept

Using the dinuclear system concept we present calculations of production cross sections for the heaviest nuclei. The obtained results are in a good agreement with the experimental data. The experimentally observed rapid fall-off of the cross sections of the cold fusion with increasing charge number Z of the compound nucleus is explained. Optimal reactions for the synthesis of the superheavy nuclei are suggested.     

Observables in nuclear fragmentation

We study the method of moments correlations as a tool to discriminate between different fragmentation mechanisms. We show, using simple models, that the variance of the fragment distribution, the size of the heaviest residue and the scaling of these quantities with the size of the fragmenting system give significant insight into the nature of the fragmentation mechanism.Unité de Recherche des Universités Paris XI et Paris VI associée au CNRS     

Calculated masses of heaviest nuclei

Masses of heaviest nuclei are calculated within a macroscopic-microscopic approach. Even-even, odd-A, and odd-odd nuclides are considered. A large region of nuclei with proton and neutron numbers of Z=82–128 and N=126–192, respectively, is analyzed. The results are compared with those of other macroscopic-microscopic and of recent microscopic Hartree-Fock-BCS calculations. Alpha-decay energies are also given.     

Systematic study of decay properties of heaviest elements

Decay properties and stability of heaviest nuclei with Z ?? 132 are studied within the macro-microscopical approach for nuclear ground-state masses. We use phenomenological relations for the half-lives with respect to ??-decay, ??-decay and spontaneous fission. Our calculations demonstrate that the ??-stable isotopes ²⁹¹Cn and ²⁹³Cn with a half-life of about 100 years are the longest-living superheavy nuclei located on the first island of stability. We found the second island of stability of superheavy nuclei in the region of Z ?? 124 and N ?? 198. It is separated from the ??continent?? by the ??gulf?? of short-living nuclei with half-lives shorted than 1 ??s.     

RI Beam Factory project at RIKEN

The RI Beam Factory is being proposed at RIKEN, which is a project to construct two superconducting ring cyclotrons (SRC-4 and SRC-6), experimental storage rings (MUSES) and experimental facilities. Heavy ions are to be accelerated to energies of up to 400 AMeV for light nuclei and 150 AMeV for the heaviest nuclei by the SRC-6 and up to 1400 AMeV in the MUSES. Wide varieties of radioactive nuclear beams are to be supplied as secondary beams. Electrons, stable nuclei, and highly charged ions in addition to radioactive nuclei can be stored in the storage rings. The MUSES provides various collision methods, such as colliding, merging, and internal target modes. A few of the selected new nuclear-physics opportunities are discussed briefly.     

超重核的四面体对称性(英文)

基于反射不对称壳模型的投影位能面计算预言原子核310126 是继208Pb 之后的双幻核,其基态呈现出四面体形状。四面体对称性驱动的量子效应可以使基态的结合能,相较球形而言增加达13 MeV,这反映了在最重核的计算中,考虑四面体自由度的重要性。计算结果还表明,四面体对称性驱动的量子效应能够明显地增加裂变位垒,从而导致超重核合成几率的增加。     

Half lives of heaviest nuclei with Woods-Saxon potential

Adapting the realistic single-particle Woods-Saxon potential the half-lives of elements withZ≧104 are estimated. Spontaneous fission, alpha decay and electron capture processes are treated. Alleven-even, odd-even andodd-odd nuclei are considered. In calculations of spontaneous fission half lives phenomenological mass parameters are applied. The results allow to estimate hindrance factors for odd systems. As compared to calculations with Nilsson model and microscopic mass parameters, present results for spontaneous fission half lives are 3–5 orders of magnitude higher in the case of heaviest nuclei (Z≧107).     

Calculated properties of superheavy nuclei

Ground-state properties of the heaviest nuclei are analyzed within a macroscopic-microscopic approach. The main attention is paid to such properties as deformation, deformation energy, energy of the first rotational state 2⁺ of a nucleus, and the branching ratio of α decay to this 2⁺ state with respect to the decay to the ground state 0⁺. The analysis concerns the problem of experimental confirmation of theoretically predicted deformed shapes of superheavy nuclei situated in the region around the nucleus ²⁷⁰Hs. A large region of even-even nuclei with proton, Z=82–128, and neutron, N=126–190, numbers is considered.     

Decay studies of N ≈ Z nuclei from 75Sr to 102Sn

Neutron deficient nuclei near ¹⁰⁰Sn have been produced by fragmentation of a 1 ^. AGeV ¹¹²Sn beam. The fragments were separated, identified and stopped in a highly segmented silicon strip detector stack. This detector measured the total energy of emitted β⁺-particles. γ-radiation was measured with surrounding detectors. The half-lives for many nuclides have been determined for the first time and give important information for the following topics: For the heaviest particle-stable odd-odd nuclei ⁹⁰Rh, ⁹⁴Ag and ⁹⁸In we observed for the first time fast β-decays, compatible with superallowed Fermi transitions and confirmed such decays for ⁷⁸Y, ⁸²Nb and ⁸⁶Tc. We have also observed long-lived T = 0 states in some of these nuclei. We measured the half-lives of all rp-process waiting-point nuclei from ⁸⁰Zr up to ^{92, 93}Pd. In addition we find the proton drip line nucleus ⁷⁷Y to decay dominantly via β-decay. To study the Gamov-Teller strength in the β-decay near the doubly magic ¹⁰⁰Sn we measured the half-life, β- and γ-spectrum of ¹⁰²Sn. We propose a level scheme for the daughter nuclide ¹⁰²In and deduce the Gamov-Teller strength (B _GT = 4.0±0.6). This is one of the largest values known. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: thomas.faestermann@ph.tum.de     

Universal properties and structure of halo nuclei

The universal properties and structure of halo nuclei composed of two neutrons (2n) and a core are investigated within an effective quantum mechanics framework. We construct an effective interaction potential that exploits the separation of scales in halo nuclei and treat the nucleus as an effective three-body system. The uncertainty from higher orders in the expansion is quantified through theoretical error bands. First, we investigate the possibility to observe excited Efimov states in 2n halo nuclei. Based on the experimental data, ²⁰C is the only halo nucleus candidate to possibly have an Efimov excited state, with an energy less than 7 keV below the scattering threshold. Second, we study the structure of ²⁰C and other 2n halo nuclei. In particular, we calculate their matter form factors, radii, and two-neutron opening angles.     

Synthesis of superheavy elements at the Dubna gas-filled recoil separator

A survey of experiments at the Dubna gas-filled recoil separator (Laboratory of Nuclear Reactions, JINR, Dubna) aimed at the detection and study of the “island of stability” of superheavy nuclei produced in complete fusion reactions of ⁴⁸Са ions and ²³⁸U–²⁴⁹Cf target nuclei is given. The problems of synthesis of superheavy nuclei, methods for their identification, and investigation of their decay properties, including the results of recent experiments at other separators (SHIP, BGS, TASCA) and chemical setups, are discussed. The studied properties of the new nuclei, the isotopes of elements 112–118, as well as the properties of their decay products, indicate substantial growth of stability of the heaviest nuclei with increasing number of neutrons in the nucleus as the magic number of neutrons N = 184 is approached.