摘要:

The damping mechanism of the damped collective motion is studied microscopically on the basis of the linear response theory. As for isovector modes the giant dipole resonance built on highly excited states in208Pbis considered. The width due to the two-body collisional damping is found to be able to reproduce well the temperature dependence of the observed width. As for isoscalar modes, the slow collective motion like fission is studied. The transport coefficients, friction &ggr;, inertiaMand local stiffnessCare computed along a fission path of224Th.The calculated effective damping rate&eegr;=&ggr;/(2M|C|)at the saddle is in qualitative agreement with the observed one which increases markedly with temperature. More realistic description of solving the transport equation is necessary to get the quantitative agreement. The approximate functional form of the friction is provided for that. Moreover, it is noticed that the effect of shell structure on the friction should be taken into account as well as the shell correction energy in the theoretical estimate of the production of super heavy elements based on the transport equation. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1372816

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The dynamical process of synthesizing superheavy elements is studied on the basis of the fluctuation-dissipative dynamics. The whole process is divided into three stages, i.e., the approaching stage, the formation stage, and the surviving stage. For the study of the formation stage, a three-dimensional Langevin equation is used from the contact of two nuclei to calculate the competition between the complete fusion and the quasi-fission. We estimate the effects of the nuclear deformation on the fusion probability. The results are consistent with the experimental results. For the description of the surviving stage, a statistical model is used to estimate the competition between the fission and the evaporation process. In this stage, it is very important to include the temperature-dependent shell correction to the fission barrier and the collective enhancement of the level density. From the study of the isotope dependence of the production cross section, the survival probability is found to be very sensitive to the separation energy of neutron. The results show the importance of the use of neutron-rich beams and targets. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1372817

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

It is shown that the compound nucleus is formed by a transfer of nucleons (dinuclear system concept) and not by a melting of the nuclei. The experimental evaporation residue cross sections and the mass distributions of quasifission products in fusion reactions leading to the production of heavy and superheavy nuclei are well reproduced in the dinuclear system model. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1372818

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The cold fusion reactions leading to superheavy elements withZ=104–116has been discussed in our model recently [5]. Presently we shortly discuss our model and extend our consideration to fusion reactions(86Kr,&hthinsp;87Rb,&hthinsp;88Sr)+208Pband86Kr+209Bileading to elements withZ=118–120.The available experimental cross-section data for the reactions are well described. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1372819

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The degrees of the deformation of nuclei at the scission points in the symmetric and asymmetric fission are experimentally determined. They are found to be constant, respectively, in a wide range ofAfamong the asymmetric fission and among the asymmetric fission of highly excited nuclei although in the latter for the spontaneous fission and low energy induced fission, the degree of deformation decreases gradually forAf>245untilAf∼260.The constancy of the degree of the scission deformation in each fission mode leads to a TKE systematic formula for each fission mode which is comparable to Viola’s TKE formula. Based on the new TKE formulas derived from the deformation parameter of the fissioning nucleus, the extension of the present knowledge to predict the fission properties of the superheavy elements is addressed. It is pointed out that the symmetric and asymmetric fission valleys may merge into one for the superheavy elements around theA=280–290region. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1372820

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We calculate complete fission potential-energy surfaces versus five shape coordinates: elongation, neck diameter, light-fragment deformation, heavy-fragment deformation, and mass asymmetry for even nuclei in the range82⩽Z⩽100.The potential energy is calculated in terms of the macroscopic-microscopic model with a folded-Yukawa single-particle potential and a Yukawa-plus-exponential macroscopic model in the three-quadratic-surface parameterization. The structure of the calculated energy landscapes exhibits multiple valleys leading to different scission configurations. The properties of these valleys and the saddle-points at the beginning of these valleys can be directly related to bimodal fission properties observed in the radium region, in the light-actinide region, and in the fermium region). The rms deviation between calculated and experimental fission-barrier heights is only 1.08 MeV for 31 nuclei from70Seto252Cf.©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1372821

出版商:AIP    

年代:1901

数据来源: AIP