摘要:

Evaporation residue production was investigated at SHIP in cold fusion reactions of Pb- and Bi-target nuclei with projectiles of elements between Ti(Z=22)and Se(Z=34)leading to compound nucleiZCN=104–116.The isotopes269110,271110,272111,and277112of the elementsZ=110,Z=111andZ=112were unambiguously identified for the first time in bombardments of208Pb,209Biwith62,64Niand70Zn.Excitation functions for50Ti+208Pband58Fe+208Pbwere measured with high precision, three new spontaneous fission (sf) activities253104,254104,258106were identified. A small &agr;-decay branch of the even-even nucleus256104(b&agr;≈0.003)was confirmed, allowing to estimate mass excesses&Dgr;mc2forN−Z=48nuclei up to264Hs(Z=108).An analysis of the &agr;-decay chains observed in a bombardment of209Biwith58Feprojectiles showed evidence for an isomeric state in266Mt(Z=109).We further report on an attempt to produce element 116 and a second isotope of element 112 by the reactions82Se+208Pband68Zn+208Pb,respectively. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55134

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The question whether the asymmetric actinide based heavy ion reactions could be used for the synthesis of heavy(Z⩾106)nuclides is essential from the point of view of the study of limitation on fusion, it is also important in such reactions new nuclides close to the magic numberN=162can be produced. Thus as the problem of a hindrance to fusion still remains unsolved the high excitation energy of the compound nucleus looks to be an obvious obstacle to using these reactions. Using the gas-filled recoil separator [1] and electrostatic recoil separator VAS-SILISSA [2] installed at the beam lines of the U-400 heavy ion cyclotron of the FLNR JINR we investigated the fusion reactions leading to 102, 103, 104, 105 and heaviest isotopes of the 106, 108 and 110 elements. The analysis of the measured cross-sections did not reveal any evidence of a hindrance to fusion at the ion bombarding energy close to the Coulomb barrier.48Ca+232Th→280110*,48Ca+238U→286112*,48Ca+244Pu→292114*appear to be the best reactions from the point of view of their cross-sections. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55135

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We first describe briefly a radioactive nuclear beam (RNB) facility based on the isotope separator on-line and post-accelerator scheme planned in Japanese Hadron Project. In this facility, various radioactive nuclear species produced in 3 GeV proton-induced reactions will be accelerated through heavy-ion linacs in three stages, the maximum output energy in each stage being 0.17, 1.05 and 6.5 meV/nucleon, respectively. Secondly, we discuss the feasibility of the use of neutron-rich RNB for experimental study of more neutron-rich superheavy nuclei than those presently known. It is shown that the increase of the survival probability of neutron-rich compound nuclei can possibly compensate for a difficulty arising from expected weak intensities of the secondary-beams. In addition, cold-fusion-like reactions as well as possible enhancement of near-barrier fusion cross sections that can become more prominent by use of neutron-rich beams are discussed. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55157

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The dinuclear system (DNS) concept of formation of compound nuclei has been applied to analysis the conditions necessary to synthesize superheavy elements (SHE). For elements 110–114 the inner fusion barriers have been calculated. Thus, it has become possible to estimate the optimal collision kinetic energy. Using the model of competition between complete fusion and quasi-fission, the formation probability of a compound nucleus in element 110–114 synthesis reactions has been calculated. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55166

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A model based on the dinuclear system concept is suggested for the calculation of the competition between complete fusion and quasifission in reactions with heavy nuclei. The fusion rate through the inner fusion barrier in mass asymmetry is found by using the Kramers-type expression. The calculated cross sections for the heaviest nuclei are in a good agreement with the experimental data. The experimentally observed rapid fall-off of the cross section of the cold fusion with increasing charge numberZof the compound nucleus is explained. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55172

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The fusion-fission process for synthesizing superheavy elements is studied on the basis of the dissipative dynamics. We use a multi-dimensional Langevin equation for the first stage where the reaction system evolves from the contact configuration of two incident nuclei to the later time when the complete dissipation of the initial relative kinetic energy is accomplished, and a two-dimensional Smoluchowski equation for the following stage. The evaporation residue cross sections for superheavy elements have been shown to have an optimum value at a certain initial energy, due to the balance between the diffusibility for fusion at high temperature and the restoration of the shell correction energy against fission at low temperature. The isotope dependence is also discussed. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55180

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Beyond uranium heavy elements rapidly become increasingly unstable with respect to spontaneous fission as the proton numberZincreases, because of the disruptive effect of the long-range Coulomb force. However, in the region just beyondZ=100magic proton and neutron numbers and the associated shell structure enhances nuclear stability sufficiently to allow observation of additional nuclei. Some thirty years ago it was speculated that an island of spherical, relatively stable superheavy nuclei would exist near the next doubly magic proton-neutron combination beyond208Pb,that is, at proton numberZ=114and neutron numberN=184.Theory and experiment now show that there also exists a rock of stability in the vicinity ofZ=110andN=162between the actinide region, which previously was the end of the peninsula of known elements, and the predicted island of spherical superheavy nuclei slightly southwest of the magic numbersZ=114andN=184.We review here the stability properties of the heavy region of nuclei. Just as the decay properties of nuclei in the heavy region depend strongly on shell structure, this structure also dramatically affects the fusion entrance channel. The six most recently discovered new elements were all formed in cold-fusion reactions. We discuss here the effect of the doubly magic structure of the target in cold-fusion reactions on the fusion barrier and on dissipation. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55136

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

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. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55183

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Theoretical results on &agr;-decay energies, &agr;-decay half-lives, dynamical fission barriers, as well as spontaneous-fission half-lives, for both deformed and spherical superheavy atomic nuclei, are presented and discussed. The calculations are based on the macroscopic-microscopic model and are performed in a multidimensional deformation space describing axially-symmetric nuclear shapes. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55137

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Starting from the contact configuration of colliding nuclei, the evolution of the nuclear shape is simulated in two-dimensional deformation space fixing the asymmetry by means of the Langevin equation under the influence of the one body dissipation. It is quantitatively shown that, in heavy mass region, the asymmetry of the entrance channel plays an important role to get an optimum fusion probability in connection with the extra barrier to be overcome. It is necessary to take into account this effect together with the excitation energy at Bass barrier to consider the optimum target-projectile combination for the synthesis of super heavy elements. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55144

出版商:AIP    

年代:1998

数据来源: AIP