摘要:

The formation of evaporation residues from compound nuclei is ultimately limited by the competition of fission and particle evaporation. In the super‐heavy elements (SHE) nuclear structure effects play a paramount role in the stabilization against spontaneous fission, e.g. the fission barrier consists entirely of the ground‐state shell effect. This work investigates the influence of this stabilization on the formation of SHE. This shell stabilization against fission for the predicted SHE island around N=184 cannot be investigated directly. The best probing ground reachable is the transition region from spherical to deformed actinides around N=126. There, the liquid‐drop part of the fission barrier and shell‐effects are of comparable magnitude. The production of these nuclei has been thoroughly investigated at GSI in fusion‐evaporation reactions of different projectile‐target combinations leading to thorium isotopes, in projectile fragmentation of uranium, and in electromagnetic‐induced fission of proton‐deficient actinides between astatine and uranium. In all these experiments the expected stabilization against fission through the spherical 126‐neutron shell is not found. Collective effects in the level density tend to cancel the shell stabilization. We conclude that spherical SHE loose at least great part of their stability against fission at rather low excitation energies and angular momenta. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737101

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Multi‐modal fission of the uranium nucleus at the low excitation energy has been dynamically investigated. The multi‐dimensional Langevin equation is used for the dynamical calculation. We used the potential energy taking account of the microscopic energy which depends on the excitation energy. We obtained the peaks of the mass distribution and the total kinetic energy (TKE) distribution. The former is consistent with experimental results and the latter is consistent with experimental systematics. We study the evolution of the mass‐asymmetry of the fragments in the dynamical process from the second saddle to the scission. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737102

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We study the collective motion of iso‐scalar type at finite excitations and concentrate on slow motion, due to the presence of a strong friction force. In the present talk the extension of approach to the case of low excitation energies, where shell effects and pairing correlation are important, is reviewed. The the case of rotating nuclei is also included. As an application of the theory, the numerical results are presented for the transport coefficients for few composite systems formed in the so called warm fusion reactions used for the synthesis of the super heavy systems. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737103

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A model of induced nuclear fission is developed with consideration of thermodynamically fluctuating orientational degree of freedom of deformed nuclei. This model was applied in analysis of the experimental angular anisotropy of fission fragments in the16O +232Th,238U and248Cm reactions at the oxygen energies from 90 to 160 MeV. Information on the equlibrating time of the orientational mode was obtained. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737104

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Nuclear dissipation in capture reactions is investigated using backtracing. Combining the analysis procedure with dynamical models, the difficult and long‐standing problem of competition and mixing of quasi‐fission and fusion‐fission is solved for the first time. At low excitation energy a new protocol able to handle low statistics data gives access to the prescission neutron multiplicity in two different systems48Ca +208Pb, Pu. The results are in agreement with a domination of fusion‐fission in the case of256No and an equal mixing of quasi‐fission and fusion‐fission in the case of Z = 114. The nature of the relevant dissipation is determined as one‐body dissipation. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737105

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The fusion‐fission process for the synthesis of superheavy elements is discussed on the basis of the fluctuation‐dissipation model. Recently the experiments at Dubna on fission of superheavy nuclei were carried out, and the mass and total kinetic energy distributions of fission fragments were measured. By analyzing the mass distribution of fission fragments, we can distinguish between fusion‐fission process and quasi‐fission process. We employ three‐dimensional Langevin equation. We find almost all of the mass symmetric fission events come from the quasi‐fission process in the superheavy mass region. In order to classify the fusion‐fission paths and compare with the experimental data directly, we analyze the pre‐scission neutron emission in the correlation with fission fragments. The neutron multiplicity depends on the travelling time of the trajectory. It is useful to investigate the fusion‐fission process. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737106

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In recent experiments at GANIL and GSI, we studied the decay of45Fe, according to theoretical predictions one of the most promissing cases for 2p radioactivity. Our results show for the first time clear evidence of this new radioactivity. In another experiment at GANIL, 2p emission was observed from excited states in17Ne. In these complete kinematics measurements performed at the SPEG facility of GANIL, the angle between the two protons has been measured evidencing a2He emission pattern. Both results will be presented and future studies are discussed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737107

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The long debate on the possible existence of neutral nuclei has been recently revived by the application of a new experimental approach, which lead to the observation of few events consistent with the formation of a bound4n in the breakup of14Be. The description of these events by a resonant (low‐energy)4n state is discussed. Finally, the preliminary results of an experiment measuring the breakup reaction (12Be, 2&agr;4n) are presented. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737108

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The decays of the neutron deficient nuclei94,95Ag,100,102In and102Sn were investigated at the GSI on‐line mass separator. The Gamow‐Teller decay of100,102In and102Sn was studied by using an array of germanium detectors and a total absorption spectrometer. In94Ag and95Ag, spin‐gap isomers were identified and their decays were investigated. Results obtained in these studies are discussed and compared to predictions of shell model calculations. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737109

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Transfer reactions offer the possibility to study single‐particle structure in exotic nuclei, including the structure of ground states, the structure of excited states, and the location and distribution of single particle strength. The last of these means that the evolution of single particle orbitals away from stability, and the consequent changes in shell structure and collectivity, can be studied in detail. The kinematics of transfer reactions initiated by protons and deuterons, in inverse kinematics, have characteristic features that mean a general‐purpose design of array can be applied to a wide range of experiments. Due to resolution considerations, coincident gamma‐ray detection is highly desirable or even essential. A new silicon detector array called TIARA has been designed so that it can be used together with the segmented germanium detectors of the EXOGAM array. The setup for TIARA is now complete, having been built by several UK groups, and it was recently commissioned by the extended UK‐France‐Spain collaboration at GANIL. The EXOGAM gamma‐ray detectors can be placed as close as 50mm to the target, covering 2/3 of 4&pgr;, so as to give the maximum detection efficiency. Simultaneously, the VAMOS magnetic spectrometer can be coupled to the system at zero degrees, to separate the beam from reaction products and give precise energy and angle measurements. The features of TIARA, as presently installed, are described. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1737110

出版商:AIP    

年代:1904

数据来源: AIP