Production Of Superheavy Nuclei Research Articles

Production of superheavy nuclei in hot-fusion reactions

Production of superheavy nuclei in hot-fusion reactions

Implication of compact configuration of hexadecapole deformed actinides in the synthesis of superheavy nuclei

The quadrupole (β2) deformed targets in the actinide region are found to be of great relevance in the production of superheavy nuclei (SHN), in the compact fusion mechanism. Recently, the application of “elongated” and “compact” configurations of pear-shape octupole (up to β3) deformed nuclei was found to play a significant role in the fusion-fission dynamics of heavy-ion induced reactions. In the present work, we intend to explore the relevance of higher-order deformed (up to β4) actinides and their compact configuration in the production cross-section as well as de-excitation of SHN (dynamics of 48Ca + 238U →286Cn∗ → A1 + A2 reaction). For the above analysis, we have calculated σER within the framework of dynamical cluster-decay model developed on the basis of quantum mechanical fragmentation theory, which has been extended with the inclusion of deformations up to β4 and corresponding compact optimum orientation. Besides, on the basis of this theory, the fragmentation structure of 286Cn∗ superheavy nucleus is examined in terms of fragmentation potential (Vη) and preformation probability (P0) as a function of fragment mass number.

The Fusion-by-Diffusion model as a tool to calculate cross sections for the production of superheavy nuclei

This article summarizes recent progress in our understanding of the reaction mechanisms leading to the formation of superheavy nuclei in cold and hot fusion reactions. Calculations are done within the Fusion-by-Diffusion (FBD) model using the new nuclear data tables by Jachimowicz et al. (At Data Nucl Data Tables 138, 101393, 2021). The synthesis reaction is treated in a standard way as a three-step process (i.e., capture, fusion, and survival). Each reaction step is analysed separately. Model calculations are compared with selected experimental data on capture, fissionlike and fusion cross sections, fusion probabilities, and evaporation residue excitation functions. The role of the angular momentum in the fusion step is discussed in detail. A set of fusion excitation functions with corresponding fusion probabilities is provided for cold and hot synthesis reactions.

Production of neutron-rich heavy nuclei around $$N = 162$$ in multinucleon transfer reactions

Within the framework of the dinuclear system model, the production mechanism of neutron-rich heavy nuclei around \(N = 162\) has been investigated systematically. The isotopic yields in the multinucleon transfer reaction of \(^{238}\)U + \(^{248}\)Cm are analyzed and compared with the available experimental data at GSI. Systematics on the production of superheavy nuclei via the collisions of \(^{238}\)U on actinide nuclides \(^{252,254}\)Cf, \(^{254}\)Es and \(^{257}\)Fm is investigated thoroughly. It is found that the shell effect is of importance in the formation of neutron-rich nuclei around \(N~=~162\) owing to the enhancement of fission barrier and neutron separation energy. The fragments in the multinucleon transfer reactions manifest the broad isotopic distribution and are dependent on the beam energy. The polar angles of the fragments tend to the forward emission with increasing the beam energy. The production cross sections of new isotopes are estimated and the heavier targets are available for the neutron-rich superheavy nucleus formation. The optimal reaction system and beam energy are proposed for the future experimental measurements.

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.

Systematics on production of superheavy nuclei $$Z = 119-122$$ in fusion-evaporation reactions

The fusion dynamics on the formation of superheavy nuclei is investigated thoroughly within the dinuclear system model. The Monte Carlo approach is implemented into the nucleon transfer process for including all possible orientations, at which the dinuclear system is assumed to be formed at the touching configuration of dinuclear fragments. The production cross sections of superheavy nuclei Cn, Fl, Lv, Ts and Og are calculated and compared with the available data from Dubna. The evaporation residue excitation functions in the channels of pure neutrons and charged particles are analyzed systematically. The combinations with $^{44}$Sc, $^{48,50}$Ti, $^{49,51}$V, $^{52,54}$Cr, $^{58,62}$Fe and $^{62,64}$Ni bombarding the actinide nuclides $^{238}$U, $^{244}$Pu, $^{248}$Cm, $^{247,249}$Bk, $^{249,251}$Cf, $^{252}$Es and $^{243}$Am are calculated for producing the superheavy elements with Z=119-122. It is found that the production cross sections sensitively depend on the neutron richness of reaction system. The structure of evaporation residue excitation function is related to the neutron separation energy and fission barrier of compound nucleus.

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 of direct production of superheavy nuclei with Z=112–118 in different evaporation channels

The production cross sections of heaviest isotopes of superheavy nuclei with charge numbers 112–118 are predicted in the xn–, pxn–, and αxn–evaporation channels of the 48Ca-induced complete fusion reactions for future experiments. The estimates of synthesis capabilities are based on a uniform and consistent set of input nuclear data. Nuclear masses, deformations, shell corrections, fission barriers and decay energies are calculated within the macroscopic-microscopic approach for even-even, odd-Z and odd-N nuclei. For odd systems the blocking procedure is used. To find saddle points, the Imaginary Water Flow technique is used and non-axiallity is taken into account. As shown, our calculations, based on a new set of mass and barriers, agree very well with the experimentally known cross-sections, especially in the 3n–evaporation channel. The dependencies of these predictions on the mass/fission barriers tables, the ratio af/a, and fusion models are discussed. A way is shown to produce directly unknown superheavy isotopes in the 1n– or 2n–evaporation channels. The synthesis of new superheavy isotopes unattainable in reactions with emission of neutrons is proposed in the promising channels with emission of protons (σpxn≃10−200 fb) and alphas (σαxn≃50−500 fb).

Fusion Dynamics of Low-Energy Heavy-Ion Collisions for Production of Superheavy Nuclei

One of the major motivation of low energy heavy-ion collision is the synthesis of superheavy nuclei. Based on the following two main aspects, various theoretical and experimental research have been performed to study the fusion dynamical process of superheavy nuclei production. The first reason is to elucidate and analyze the synthesis mechanism of superheavy nuclei; the other is to search the favorable incident energy and the best combination of projectile and target to produce new superheavy elements and isotopes of superheavy elements.

Possibilities of producing superheavy nuclei in multinucleon transfer reactions based on radioactive targets * * Supported by the National Natural Science Foundation of China (11605296); the Natural Science Foundation of Guangdong Province, China (2016A030310208); and Fundamental Research Funds for the Central Universities (18lgpy87)

The multinucleon transfer (MNT) process has been proposed as a promising approach to produce neutron-rich superheavy nuclei (SHN). MNT reactions based on the radioactive targets 249Cf, 254Es, and 257Fm are investigated within the framework of the improved version of a dinuclear system (DNS-sysu) model. The MNT reaction 238U + 238U was studied extensively as a promising candidate for producing SHN. However, based on the calculated cross-sections, it was found that there is little possibility to produce SHN in the reaction 238U + 238U. In turn, the production of SHN in reactions with radioactive targets is likely.

Simulation of fusion and quasi-fission in nuclear reactions leading to production of superheavy elements using the Constrained Molecular Dynamics model

Fusion dynamics and the onset of quasi-fission in reactions, leading to production of superheavy nuclei are investigated using the constrained molecular dynamics model. Constraints on the parameters of the nuclear equation of state are derived from experimental fusion probabilities. The obtained constraint on the modulus of incompressibility of nuclear matter K0=240−260 MeV is consistent with the results of previous study using the Boltzmann-Uehling-Uhlenbeck equation and also with constraints derived using the recent neutron star binary collision event GW170817. Unlike the modulus of incompressibility of symmetric nuclear matter, the stiffness of the density-dependence of symmetry energy influences the fusion probability only weakly.

The role of the Heisenberg principle in constrained molecular dynamics model

We implement the Heisenberg principle into the Constrained Molecular Dynamics model with a similar approach to the Pauli principle using the one-body occupation probability [Formula: see text]. Results of the modified and the original model with comparisons to data are given. The binding energies and the radii of light nuclei obtained with the modified model are more consistent with the experimental data than the original one. The collision term and the density distribution are tested through a comparison to p+[Formula: see text]C elastic scattering data. Some simulations for fragmentation and superheavy nuclei production are also discussed.

Predictions for production of superheavy nuclei with Z = 105–112 in hot fusion reactions

The effects of mass asymmetry on the production of superheavy nuclei (SHN), within the dinuclear system model, are investigated in this study. It is observed that the fusion probability decreases with decreasing mass asymmetry. A total of 192 possible combinations of projectiles from O to Ti and targets with half-lives longer than 30 days for producing SHN $$^{264}\text {Db}$$ , $$^{265}\text {Db}$$ , $$^{267}\text {Sg}$$ , $$^{268}\text {Bh}$$ , $$^{268}\text {Sg}$$ , $$^{269}\text {Bh}$$ , $$^{271}\text {Hs}$$ , $$^{271}\text {Mt}$$ , $$^{272}\text {Hs}$$ , $$^{272}\text {Mt}$$ , $$^{273}\text {Mt}$$ , $$^{274}\text {Ds}$$ , $$^{275}\text {Ds}$$ , $$^{275}\text {Rg}$$ , $$^{276}\text {Ds}$$ , $$^{276}\text {Rg}$$ , $$^{277}\text {Rg}$$ , $$^{278}\text {Cn}$$ , $$^{279}\text {Cn}$$ , and $$^{280}\text {Cn}$$ are examined. Further, the optimal combinations and incident energies for synthesizing these nuclei are predicted. Most of the cross sections for production of SHN are larger than 10 pb; therefore, the process can be carried out with the available experimental equipment.

Synthesis and decay process of superheavy nuclei with Z=119-122 via hot-fusion reactions

In this research article attempts have been made to calculate the superheavy-nuclei synthesis characteristics including, the potential energy parameters, fusion probability, fusion and evaporation residue (ER) cross sections as well as, decay properties of compound nucleus and the residue nuclei formation probability for elements with Z=119-122 by using the hot-fusion reactions. It is concluded that, although a selection of double magic projectiles such as 48Ca with high binding energy, simplifies the calculations significantly due to spherical symmetric shape of the projectile, resulting in high evaporation residue cross section, unfortunately, nuclei with $ Z > 98$ do not exist in quantities sufficient for constructing targets for the hot-fusion reactions. Therefore, practically our selection is fusion reactions with titanium projectile because the mass production of target nuclei for experimental purposes is more feasible. Based upon our findings, it is necessary, for new superheavy-nuclei production with $ Z > 119$ , to use neutron-rich projectiles and target nuclei. Finally, the maximal evaporation residue cross sections for the synthesis of superheavy elements with Z=119-122 have been calculated and compared with the previously founded ones in the literature.

Description of quasifission reactions in the dinuclear system model

The formation and evolution of dinuclear systems in quasifission reactions are investigated. The process of formation of reaction products is analyzed based on the concept of a dinuclear system. Isotopic trends of cross sections of production of superheavy nuclei in quasifission reactions are discussed. The yields of new neutron-rich isotopes of nuclei with Z = 64–80 in quasifission reactions are predicted. The mechanism of production of complex fragments in complete fusion and quasifission reactions is analyzed.

A novel approach to the island of stability of super-heavy elements search

It is expected that the cross section for super-heavy nuclei production of Z > 118 is dropping into the region of tens of femto barns. This creates a serious limitation for the complete fusion technique that is used so far. Moreover, the available combinations of the neutron to proton ratio of stable projectiles and targets are quite limited and it can be difficult to reach the island of stability of super heavy elements using complete fusion reactions with stable projectiles. In this context, a new experimental investigation of mechanisms other than complete fusion of heavy nuclei and a novel experimental technique are invented for our search of super- and hyper-nuclei. This contribution is focused on that technique.

Cross sections for the production of superheavy nuclei

Production and studying properties of superheavy (SH) nuclei meet significant experimental difficulties owing to extremely low cross sections of their formation in heavy ion fusion or multinucleon transfer reactions. Accurate predictions of these cross sections along with the corresponding excitation functions are quite desirable for planning and performing experiments of such kind. Study of these cross sections (their dependence on projectile–target combination and energy dependence) gives us an opportunity to investigate complicated dynamics of low-energy heavy ion collisions as well as decay properties of excited SH nuclei.

Cold fission from isomeric states of superheavy nuclei

Correlations between the potential energy surface structure and the mass distributions observed in the production of superheavy nuclei are evidenced. The isomeric states are identified by spanning the multidimensional configuration space from the contact point of the colliding nuclei up to the formation of the compound nucleus. The available degrees of freedom are the elongation, the necking, the mass asymmetry, and the deformations of the two colliding nuclei. Using the macroscopic-microscopic model based on the Woods-Saxon two-center shell model, several minima in the potential energy landscape were revealed. The fission process from these isomeric states was investigated and the probabilities of realization of possible partitions were calculated in the WKB approximation. The inertia was computed in the framework of the cranking model. The identified correlations indicate that the mass distribution attributed to quasifission in previous studies can be alternatively explained as a cold-fission process from excited states.

Impact of nuclear structure on production of superheavy nuclei

The calculations performed with the modified two-center shell model reveal quite strong shell effects at Z = 120 – 126 and N = 184 as in the self-consistent mean-field treatments. If our prediction of the structure of heaviest nuclei is correct, than one can expect the production of evaporation residues Z = 120 in the reactions50Ti+249Cf and 54Cr+248Cm in near future. The nuclear level densities were calculated for the nuclei of a-decay chains containing 296,298,300120. The minima of the level density parameter clearly indicate the strong shell effect at Z = 120.

Study of nuclear dynamical deformation in the synthesis of super-heavy nuclei

The nuclear dynamical deformations in the fusion reactions for the production of superheavy nuclei (SHN) are studied within the framework of the di-nuclear system model with dynamical potential energy surface (DNS-DynPES model). The development of the dynamical deformation for the incident channel is investigated and the maximum dynamical deformations for different configurations are also calculated. The influences of the dynamical deformations on the potential energy surface (PES) and the fusion probability are also calculated. The results indicate that the structure of the PES changes significantly and the fusion for synthesizing SHN is also hindered for the inclusion of the nuclear dynamical deformation. The fusion probability as a function of angular momentum is also investigated.