Nuclei In Cold Fusion Reactions Research Articles

Diffusion as a possible mechanism controlling the production of superheavy nuclei in cold fusion reactions

The fusion probability for the production of superheavy nuclei in cold fusion reactions was investigated and compared with recent experimental results for $^{48}$Ca, $^{50}$Ti, and $^{54}$Cr incident on a $^{208}$Pb target. Calculations were performed within the fusion-by-diffusion model (FbD) using new nuclear data tables by Jachimowicz et al. It is shown that the experimental data could be well explained within the framework of the FbD model. The saturation of the fusion probability at bombarding energies above the interaction barrier is reproduced. It emerges naturally from the physical effect of the suppression of contributions of higher partial waves in fusion reactions and is related to the critical angular momentum. The role of the difference in values of the rotational energies in the fusion saddle point and contact (sticking) configuration of the projectile-target system is discussed.

Production of super-heavy nuclei in cold fusion reactions

A model for cold-fusion reactions related to the synthesis of super-heavy nuclei in collisions of heavy projectile-nuclei with a 208Pb target nucleus is discussed. In the framework of this model, the production of the compound nucleus by two paths, the di-nuclear system path and the fusion path, are taken into account simultaneously. The formation of the compound nucleus in the framework of the di-nuclear system is related to the transfer of nucleons from the light nucleus to the heavy one. The fusion path is linked to the sequential evolution of the nuclear shape from the system of contacting nuclei to the compound nucleus. It is shown that the compound nucleus is mainly formed by the fusion path in cold-fusion reactions. The landscape of the potential energy related to the fusion path is discussed in detail. This landscape for very heavy nucleus-nucleus systems has an intermediate state, which is linked to the formation of both the compound nucleus and the quasi-fission fragments. The decay of the intermediate state is taken into account in the calculation of the compound nucleus production cross sections and the quasi-fission cross sections. The values of the cold-fusion cross sections obtained in the model agree well with the experimental data.

Possibilities for synthesis of new isotopes of superheavy nuclei in cold fusion reactions

In order to find a way to produce superheavy nuclei (SHN), which appear in the gap between the SHN synthesized by cold fusion and those by hot fusion, or those so far not yet been produced in the laboratory, we tried to make use of a set of projectile isotopic chains, to use a radioactive beam projectile, and to test symmetric fusion reactions for gaining more neutrons to synthesize neutron-richer SHN based on the dinuclear system (DNS) model via cold fusion reactions. It is found that the nuclei (265)Mt, (268,272)Ds, (273)Rg, and (274,275,276)Cn may be produced with the detectable evaporation residual cross sections. The intensities of radioactive beams are significantly less than those of the stable beams, therefore using a stable beam is predicted to be the most favorable method for producing SHN. From the symmetric reaction system Xe-136 + Xe-136, no fusion event was found.

Synthesis of the heaviest nuclei in cold fusion reactions

Synthesis of the heaviest nuclei in cold fusion reactions

Nucleus-nucleus cold fusion reactions analyzed with thel-dependent “fusion by diffusion” model

We present a modified version of the Fusion by Diffusion (FBD) model aimed at describing the synthesis of superheavy nuclei in cold fusion reactions, in which a low excited compound nucleus emits only one neutron. The modified FBD model accounts for the angular momentum dependence of three basic factors determining the evaporation residue cross section: the capture cross section ${\ensuremath{\sigma}}_{\text{cap}}(l)$, the fusion probability ${P}_{\text{fus}}(l)$, and the survival probability ${P}_{\text{surv}}(l)$. The fusion hindrance factor, the inverse of ${P}_{\text{fus}}(l)$, is treated in terms of thermal fluctuations in the shape degrees of freedom and is expressed as a solution of the Smoluchowski diffusion equation. The $l$ dependence of ${P}_{\text{fus}}(l)$ results from the $l$-dependent potential energy surface of the colliding system. A new parametrization of the distance of starting point of the diffusion process is introduced. An analysis of a complete set of 27 excitation functions for production of superheavy nuclei in cold fusion reactions, studied in experiments at GSI Darmstadt, RIKEN Tokyo, and LBNL Berkeley, is presented. The FBD model satisfactorily reproduces shapes and absolute cross sections of all the cold fusion excitation functions. It is shown that the peak position of the excitation function for a given 1$n$ reaction is determined by the $Q$ value of the reaction and the height of the fission barrier of the final nucleus. This fact could possibly be used in future experiments (with well-defined beam energy) for experimental determination of the fission barrier heights.

Synthesis of transactinide nuclei in cold fusion reactions using radioactive beams

Chances of synthesis of transactinide nuclei in cold fusion reactions (one-neutron-out reactions) using radioactive beams are evaluated. Because in most of the cases intensities of radioactive beams are significantly less than those of the stable beams, reactions with the greatest radioactive-beam intensities for the particular elements are considered. The results are compared with the recent ones obtained by Loveland [Phys. Rev. C 76, 014612 (2007)], who investigated the same nuclei.

Formation of superheavy nuclei in cold fusion reactions

Within the concept of the dinuclear system (DNS), a dynamical model is proposed for describing the formation of superheavy nuclei in complete fusion reactions by incorporating the coupling of the relative motion to the nucleon transfer process. The capture of two heavy colliding nuclei, the formation of the compound nucleus, and the de-excitation process are calculated by using an empirical coupled channel model, solving a master equation numerically and applying statistical theory, respectively. Evaporation residue excitation functions in cold fusion reactions are investigated systematically and compared with available experimental data. Maximal production cross sections of superheavy nuclei in cold fusion reactions with stable neutron-rich projectiles are obtained. Isotopic trends in the production of the superheavy elements $Z=110,$ 112, 114, 116, 118, and 120 are analyzed systematically. Optimal combinations and the corresponding excitation energies are proposed.

Entrance Channel Dependence of Production Cross Sections ofSuperheavy Nuclei in Cold Fusion Reactions

Production cross sections of superheavy nuclei Rf and Hs forasymmetric and nearly symmetric projectile-target combinations aresystematically studied within the framework of the dinuclear systemmodel. The calculated results show that the production crosssections are strongly dependent on the symmetry of reactionsystems. The obtained results are in good agreement with theavailable experimental data for asymmetric reaction systems. Fornearly symmetric systems, the model gives opposite results withcoupled channel model in which surface vibration andnucleon transfer are included.

Cluster expression in fission and fusion in high-dimensional macroscopic–microscopic calculations

We discuss the relation between the fission-fusion potential-energy surfaces of very heavy nuclei and the formation process of these nuclei in cold-fusion reactions. In the potential-energy surfaces, we find a pronounced valley structure, with one valley corresponding to the cold-fusion reaction, the other to fission. As the touching point is approached in the cold-fusion entrance channel, an instability towards dynamical deformation of the projectile occurs, which enhances the fusion cross section. These two 'cluster effects' enhance the production of superheavy nuclei in cold-fusion reactions, in addition to the effect of the low compound-system excitation energy in these reactions. Heavy-ion fusion reactions have been used extensively to synthesize heavy elements beyond actinide nuclei. In order to proceed further in this direction, we need to understand the formation process more precisely, not just the decay process. The dynamics of the formation process are considerably more complex than the dynamics necessary to interpret the spontaneous-fission decay of heavy elements. However, before implementing a full dynamical description it is useful to understand the basic properties of the potential-energy landscape encountered in the initial stages of the collision. The collision process and entrance-channel landscape can conveniently be separated into two parts, namely the early-stage separatedmore » system before touching and the late-stage composite system after touching. The transition between these two stages is particularly important, but not very well understood until now. To understand better the transition between the two stages we analyze here in detail the potential energy landscape or 'collision surface' of the system both outside and inside the touching configuration of the target and projectile. In Sec. 2, we discuss calculated five-dimensional potential-energy landscapes inside touching and identify major features. In Sec. 3, we present calculated 'collision surfaces' for still separated targets and projectiles. Implications for SHE formation are discussed. Section 4 is a short summary of the present analysis.« less

Isotopic trends in the production of superheavy nuclei in cold fusion reactions

In the $^{208}\mathrm{Pb}$-based cold fusion-evaporation reactions the dependence of the yield of heaviest nuclei on the isotopic composition of the projectile nucleus is studied within the dinuclear system model for compound nucleus formation. Projectiles with a larger number of neutrons are not expected to increase always the production cross section of superheavy nuclei. New optimal reactions for the synthesis of superheavy nuclei with $Z=112$ and 114 are suggested.

Cross-section limits for the 208 Pb(86 Kr,n)293118 reaction

In April-May, 2001, the previously reported experiment to synthesize element 118 using the $^{208}$Pb($^{86}$Kr,n)$^{293}$118 reaction was repeated. No events corresponding to the synthesis of element 118 were observed with a total beam dose of 2.6 x 10$^{18}$ ions. The simple upper limit cross sections (1 event) were 0.9 and 0.6 pb for evaporation residue magnetic rigidities of 2.00 $T m$ and 2.12 $T m$, respectively. A more detailed cross section calculation, accounting for an assumed narrow excitation function, the energy loss of the beam in traversing the target and the uncertainty in the magnetic rigidity of the Z=118 recoils is also presented. Re-analysis of the primary data files from the 1999 experiment showed the reported element 118 events are not in the original data. The current results put constraints on the production cross section for synthesis of very heavy nuclei in cold fusion reactions.

Production of Even-Even Superheavy Nuclei in Cold Fusion Reactions

Production of Even-Even Superheavy Nuclei in Cold Fusion Reactions

Excitation functions for the production of superheavy nuclei in cold fusion reactions

Excitation energy dependence of the cross sections of the reactions ${}^{208}{\mathrm{Pb}}_{126}{(}^{50}{\mathrm{Ti}}_{28}{,1n)}^{257}{\mathrm{Rf}}_{153}$ and ${}^{208}{\mathrm{Pb}}_{126}{(}^{58}{\mathrm{Fe}}_{32}{,1n)}^{265}{\mathrm{Hs}}_{157}$ is calculated and compared with the experimental data measured at GSI-Darmstadt. Such a dependence is also calculated for the reaction ${}^{208}{\mathrm{Pb}}_{126}{(}^{86}{\mathrm{Kr}}_{50}{,1n)}^{293}{118}_{175}$ reported recently by the Berkeley group, and for reactions which may lead to the synthesis of element 119 and production of its odd-$Z$ descendants. Recommendations for future experiments based on the present study are presented.

Production mechanism of superheavy nuclei in cold fusion reactions

A relatively simple model which reproduces the measured formation cross sections of deformed superheavy nuclei synthesized in cold fusion reactions is proposed. Within this model, optimal bombarding energies and formation cross sections of the hypothetical spherical superheavy nuclei are predicted.