Synthesis Of Superheavy Nuclei Research Articles

Phosphate Glass Detectors for Heavy Ion Identification

The problem of the boundaries of the Mendeleev table of chemical elements is closely related to the understanding of the properties of nuclear matter. In this regard, the synthesis of superheavy nuclei on accelerators and the registration of their decay products are of fundamental scientific interest. The Joint Institute of Nuclear Research in Dubna (JINR) conducts research on the synthesis of superheavy nuclei on the new DC-280 cyclotron (the Factory of Superheavy Elements). As part of the development of this experiment, the possibility of using phosphate glass as a material for detectors of heavy and superheavy nuclei is being considered. This issue requires test experiments to study the recording properties of the glass at different irradiation and treatment conditions. The article presents a method for identifying heavy ions in phosphate glass detectors under various conditions by the geometric characteristics of ion tracks. The results obtained indicate the possibility of using the KNFS-3 phosphate glass detectors for registration and identification of accelerated superheavy nuclei.

Competition between weak and α -decay modes in superheavy nuclei

The competition between $\ensuremath{\alpha}$- and ${\ensuremath{\beta}}^{+}/\text{EC}$-decay modes is studied systematically in nuclei along the $\ensuremath{\alpha}$-decay chains following the synthesis of superheavy nuclei with $Z=119$ and $Z=120$. A microscopic approach based on deformed self-consistent Hartree-Fock mean-field calculations with Skyrme forces and pairing correlations is used to describe the ${\ensuremath{\beta}}^{+}$ and electron capture weak decays, whereas the $\ensuremath{\alpha}$ decay is estimated from existing phenomenological expressions. It is shown that $\ensuremath{\alpha}$ decay is in most cases the dominant decay mode, but interesting instances are identified where the half-lives are comparable, opening the possibility of new pathways towards more neutron-rich nuclei in this region.

Study of the Synthesis of Super Heavy Nuclei Based on Dinuclear System

Study of the Synthesis of Super Heavy Nuclei Based on Dinuclear System

Effects of beam wobbling and target rotation on the target temperature in experiments with intense heavy ion beams

Effects of beam wobbling and target rotation on reducing target temperature are quantitatively considered with simulations and calculations. These manipulations with the beam and target reduce sharpness in the beam-density distribution, making it quasiuniform on the target surface. A uniform beam density is essential in prolonged experiments on the synthesis of superheavy nuclei using intense heavy-ion beams and actinide targets. The heavy-ion beam energy partially absorbed by the target and target backing heats them and transfers warmth to the surrounding by different means. The target temperature was initially considered for a stationary target using notions of heat transfer due to the thermal conductivity, radiation emission, and heat removal to dilute gas surrounding the target. The effects of the beam width, the amplitude of the wobbler, and the rotating target velocity on the beam-density distribution across the target surface and, consequently, on its temperature are further estimated with the same notions.

Radioactive ion beam physics related to HIAF

This article aims to describe the key scientific problems, historical developments and prospects of the radioactive ion beam (RIB) physics. There exist only less than 300 stable nuclides in the universe, whereas the the number of unstable nuclei can be as high as 10000. The production and study of such radioactive nuclides (RIB physics) are an exploration of an undiscoveredarea, which necessities new experimental tools and theoretical models. Numerous new findings have been reported at the initial stage ofRIB physics research based on new observations. Typical examples include the halo and cluster structures, new magic numbers, shellevolution and soft dipole resonances. The study of unstable nuclei is also closely related to that of nuclear astrophysics processes as well as the synthesis of superheavy nuclei, which are belonging to the most important interdisciplinary problems worldwide. Investigations on unstable nucleus provide experimental data for nuclear energy systems; thus, they have strategic application value. The advantages of HIAF are associated with high beam intensity. When combined with advanced technologies for RIB separation and experimental detection, HIAF would play certain leading roles in the international community.

Investigations on the study of entrance channel effects in synthesis of superheavy elements using Cr-induced fusion reactions

We have investigated the synthesis of superheavy elements using Cr-induced fusion reactions. We have studied all possible Cr-induced fusion reactions for the synthesis of super heavy nuclei [Formula: see text]. We have achieved the semi-empirical formula for fusion barrier heights ([Formula: see text]), positions ([Formula: see text]), curvature of the inverted parabola ([Formula: see text]) of Cr-induced fusion reactions for the synthesis of superheavy nuclei with atomic number range [Formula: see text]. The proposed formula produces fusion barriers of Cr-induced fusion reactions for the synthesis of super heavy nuclei with the simple inputs of mass number ([Formula: see text]) and atomic number ([Formula: see text]) of projectile-targets. We have also identified the targets for Cr-induced fusion reactions to synthesis superheavy elements of [Formula: see text]. We have also studied the entrance channel parameters such as mass asymmetry ([Formula: see text]), charge asymmetry ([Formula: see text]), coulomb interaction parameter ([Formula: see text]’), Businaro–Gallone mass asymmetry parameter ([Formula: see text]) and Isospin asymmetry parameter [[Formula: see text]]. We hope that our predictions may be the guide for the future experiments in the synthesis of more superheavy elements using [Formula: see text]Cr-induced fusion reactions.

Modification of Ti foils irradiated by intense heavy ion beams

ABSTRACT Modification of Ti foils irradiated by intense energetic heavy ion (HI) beams in long-term experiments has been considered. The experiments on the synthesis of superheavy nuclei, which are carried out in Dubna with a gas-filled recoil separator (DGFRS), determine the conditions of such experiments. High intensities of HIs passing through a relatively small area and thickness of the foils, as well as their heating by a beam, are inherent in such experiments. The ability of the foils to withstand radiation damages, sputtering, and evaporation of atoms becomes questionable. All the processes seem to be dependent on temperature, and none of them is independent of the others, but they can be considered separately. In this work, sputtering yields are estimated on the grounds of available models and experimental data and compared with the results of measurements carried out to verify the estimates. The foil temperature, in turn, can be estimated in the conditions of pulse heating followed by subsequent cooling with radiation emitted from their surfaces. These conditions correspond to the rotating Ti entrance window irradiated by a continuous HI beam in the DGFRS experiments.

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.

Evaporation residue cross section to synthesize superheavy element Z=119

The evaporation-residue cross section σEVR of fusion reactions depend on the projectile-target combinations and the incident energy. A detail theoretical study is useful before the synthesis of more isotopes of super heavy nuclei Z=119. We have studied the evaporation-residue cross sections for possible projectile-target combinations to synthesis the superheavy nuclei with Z=119. We have studied the dependence of evaporation residue cross section with that of mass number of the target, product of atomic numbers of projectile and target (Z1Z2), fusion barrier height (Vb) and fusion barrier width (Rb). After the detailed analysis, we have identified the most probable projectile-target combinations. The identified projectile-target combinations to synthesis superheavy nuclei 295-296119 are 45Sc+250,251Cf. We hope that our predictions guide the future experiments in the synthesis of super heavy nuclei 295-296119.

Competition between binary fission, ternary fission, cluster radioactivity and alpha decay of 281Ds

The competition between different decay modes such as binary fission, ternary fission, cluster and alpha decay modes finds an important role in the synthesis of superheavy nuclei. The nuclei 281Ds is the most stable among the isotopes of Ds. We have studied the different decay modes in superheavy nuclei 281Ds. It is observed that alpha decay half-lives are smaller compared to other modes. The alpha decay mode of 281Ds is observed with greater probability compared to binary fission.

Improved evaluation of nuclear charge radii for superheavy nuclei

Although significant progress has been made in the synthesis of superheavy nuclei, the experimental knowledge of them is still very limited while the alpha decay chain is the main tool used to identify newly produced superheavy nuclei. Previously, we have extracted nuclear charge radii of superheavy nuclei via the experimental alpha decay data. As a further step, the density dependent cluster model is improved by introducing the difference between the density distributions of protons and neutrons. Besides, the important quantity, i.e., the alpha preformation factor, is connected with the microscopic correction of nuclear mass during this procedure, to perform a more reasonable description of the alpha decay process. It is found that the present deduced nuclear charge radii of heavy nuclei are in a better agreement with the measured values as compared to those in our previous evaluations. Subsequently, the nuclear radii of heavier even–even isotopes with Z = 98–116 are probed, accompanied by the consistency with the empirical evaluations. Moreover, the effect of the depressed density at the center of superheavy nucleus on the final extracted nuclear radius plus the decay lifetime is discussed, which appears to be different from the case of lighter nuclide.

A probability of synthesis of the superheavy element Z=124

We have studied the fusion cross section, evaporation residue cross secion, compound nucleus formation probability ( $P_{CN}$ ) and survival probability ( $P_{sur}$ ) of different projectile target combinations to synthesize the superheavy element Z=124. Hence, we have identified the most probable projectile-target combination to synthesize the superheavy element Z = 124 . To synthesize the superheavy element Z=124, the most probable projectile target combinations are Kr+Ra, Ni+Cm, Se+Th, Ge+U and Zn+Pu. We hope that our predictions may be a guide for the future experiments in the synthesis of superheavy nuclei Z=124.

Durability of targets and foils irradiated by intense heavy ion beams in experiments on synthesis of superheavy nuclei

Durability of targets and window foils irradiated by intense heavy ion (HI) beams in the experiments on synthesis of superheavy nuclei, which are carried out in Dubna with Gas-Filled Recoil Separator (DGFRS), has been viewed in various ways. High fluxes of HI and heat generations, which are realized within relatively small areas and thicknesses of these elements of DGFRS, are inherent in such experiments. The lifetimes of the targets and window foils are estimated as the result of HI beam actions such as radiation damages, sputtering and evaporation of atoms. The most critical processes determining the durability of the targets and window foils are discussed. The processes of heat transfer due to thermal conductivity, convection and radiation are also considered from the point of view of possible ways of cooling of the elements irradiated by an intense HI beam. Temperatures of the targets and window foils as functions of time are calculated in the conditions of their pulse heating by the beam followed by radiative cooling of their surfaces. Such pulsing mode is realized in the DGFRS operation with the rotation of target and window foils irradiated by a continuous HI beam. Estimates show that radiative cooling in such conditions can be the most effective way of heat removal at the temperature of several hundred degrees. Such temperature can be reached on the surfaces of the target and window foils irradiated by HI beams at the intensity ~1013 s–1.

Projectile target combination to synthesis superheavy nuclei Z = 126

We have studied the fusion cross section, survival cross section, fission cross section, compound nucleus formation probability (PCN) and survival probability (PSurv) of superheavy nuclei 126307, 126318, 126319, and 126320. Hence, we have identified the most probable projectile–target combination to synthesis these superheavy nuclei. From the detail study of these parameters, it is clear that for the superheavy nuclei 126307, the projectile target combinations such as 54Fe + 253Fm and 58Ni + 249Cf are most probable projectile target combination for synthesis. The projectile target combinations such as 64Ni + 254Cf and 80Se + 238U are most probable projectile target combination for the synthesis of 126318. The projectile target combinations such as 72Zn + 247Cm and 66Ni + 253Cf are most probable projectile target combination for synthesis the superheavy nuclei 126319. The projectile target combinations such as 66Ni + 254Cf and 82Se + 238U are most probable projectile target combination for synthesis the superheavy nuclei 126320. Thus, we hope that our predictions may be guide for the future experiments in the synthesis of superheavy nuclei Z=126.

Systematic study of the heavy-ion fusion dynamics at near-barrier energies

In recent decades, the study of capture and fusion dynamics in heavy-ion collisions has been a subject of intense experimental and theoretical interests because the heavy-ion capture not only is of central importance for nucleosynthesis but also can reveal rich interplay between nuclear structure and reaction dynamics. Theoretically, the heavy-ion capture and fusion processes at energies near the Coulomb barrier can be treated as a multidimensional barrier penetration problem. The multidimensional barrier penetration process can be described by solving the coupled-channel equations, i.e., the coupled-channel (CC) model. However, for heavy reaction systems, it is necessary to take into account a large number of channels which is not easy to realize in the CC model. Moreover, the structure information of the interacting nuclei are needed as inputs. Therefore, full CC calculations become intractable in many cases including many fusion reactions leading to superheavy nuclei. On the other hand, in the eigenchannel framework, the couplings to other channels split the single potential barrier into a set of discrete barriers. Based on the concept of the barrier distribution, several empirical CC approaches have been developed. Recently, we have developed an empirical coupled-channel (ECC) model and performed a systematic study of capture excitation functions for 220 reaction systems. In this ECC model, an asymmetric Gaussian-form barrier distribution function was used to take effectively into account the effects of inelastic excitation couplings and neutron transfer coupling. Based on the interaction potential between the projectile and the target, empirical formulas were proposed for the parameters of the barrier distribution according to the static and dynamical deformations of the two colliding nuclei. For the vibrational coupling effect and the rotational coupling effect, the parameters of the empirical formulas were given, respectively. For spherical reaction systems (vibrational coupling effect), the width of the barrier distribution increases with the charge product of the reaction system, while for the deformed reaction systems (rotational coupling effect), besides the charge product of the reaction system, the width of the barrier distribution is also related to the static deformation parameters of the projectile and the target. For some reaction systems, the coupling effects of the positive Q -value neutron transfer (PQNT) channels are needed to explain the enhancement of sub-barrier capture cross sections. In this ECC model, the effects of PQNT are simulated by broadening the barrier distribution. Moreover, the positive Q value for one neutron pair transfer is used to broaden the barrier distribution in the present model. Among these 220 reaction systems, there are 89 systems with positive Q value for one neutron pair transfer channel. The calculated capture cross sections of most of these 89 reaction systems are in good agreement with the experimental values, which implies that the Q value for one neutron pair transfer is very important to understanding of the coupling to PQNT channels. Generally speaking, the ECC model together with the empirical formulas for parameters of the barrier distribution works quite well in the description of the capture cross sections at near-barrier energies. This model can provide useful information on capture dynamics and predictions of capture cross sections for the synthesis of superheavy nuclei. In the present paper, we will review this ECC model and its applications.

Estimation of evaporation residue cross section for the synthesis of superheavy nuclei

To estimate the evaporation residue cross section of superheavy nuclei, we clarify the parameter dependence of the models. At the first attempt, we focus our attention on the parameters of the statistical model, and investigate the parameter dependence of the survival probability. Then we discuss the the evaporation residue cross section for each parameter.

Synthesis of superheavy elements at the Dubna gas-filled recoil separator

A survey of experiments at the Dubna gas-filled recoil separator (Laboratory of Nuclear Reactions, JINR, Dubna) aimed at the detection and study of the “island of stability” of superheavy nuclei produced in complete fusion reactions of 48Са ions and 238U–249Cf target nuclei is given. The problems of synthesis of superheavy nuclei, methods for their identification, and investigation of their decay properties, including the results of recent experiments at other separators (SHIP, BGS, TASCA) and chemical setups, are discussed. The studied properties of the new nuclei, the isotopes of elements 112–118, as well as the properties of their decay products, indicate substantial growth of stability of the heaviest nuclei with increasing number of neutrons in the nucleus as the magic number of neutrons N = 184 is approached.

Synthesis of superheavy nuclei: Obstacles and opportunities

There are only 3 methods for the production of heavy and superheavy (SH) nuclei, namely, fusion reactions, a sequence of neutron capture and beta(-) decay and multinucleon transfer reactions. Low values of the fusion cross sections and very short half-lives of nuclei with Z>120 put obstacles in synthesis of new elements. At the same time, an important area of SH isotopes located between those produced in the cold and hot fusion reactions remains unstudied yet. This gap could be filled in fusion reactions of 48 Ca with available lighter isotopes of Pu, Am, and Cm. New neutron-enriched isotopes of SH elements may be produced with the use of a 48 Ca beam if a 250 Cm target would be prepared. In this case we get a real chance to reach the island of stability owing to a possible beta(+) decay of 291 114 and 287 112 nuclei formed in this reaction with a cross section of about 0.8 pb. A macroscopic amount of the long-living SH nuclei located at the island of stability may be produced by using the pulsed nuclear reactors of the next generation only if the neutron fluence per pulse will be increased by about three orders of magnitude. Multinucleon transfer processes look quite promising for the production and study of neutron-rich heavy nuclei located in upper part of the nuclear map not reachable by other reaction mechanisms. Reactions with actinide beams and targets are of special interest for synthesis of new neutron-enriched transfermium nuclei and not-yet-known nuclei with closed neutron shell N=126 having the largest impact on the astrophysical r-process. The estimated cross sections for the production of these nuclei allows one to plan such experiments at currently available accelerators.

Alpha decay properties of heavy and superheavy elements

Analysing accurately the lifetimes of α-decay chains is an important tool to detect and study the properties of superheavy nuclei. 48Ca is used in the synthesis of superheavy nuclei Z = 106−118 at Dubna. The experimental work of 48Ca projectiles at Dubna has given an opportunity to study the superheavy element (SHE). Here, the α-decay properties for Z = 106–118 are evaluated using our CYE model and are compared with the available experimental and theoretical values.

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.