Synthesis Of Superheavy Elements Research Articles

Survival probability of Selenium-induced fusion reactions

In this paper, we investigated every potential scenario for selenium-induced heavy ion fusion reactions using astatine isotopes as the target. In this context, we examined [Formula: see text]Se projectiles and [Formula: see text]At targets having longer half-lives of comprising 21 fusion reactions for the synthesis of superheavy element [Formula: see text]. We assessed fusion cross-sections ([Formula: see text]), compound nucleus formation probability ([Formula: see text]), and survival probability ([Formula: see text]) for [Formula: see text]Se projectiles on [Formula: see text]At targets. The evaporation residue cross-sections ([Formula: see text]) is found to be larger for the fusion reaction of [Formula: see text]At of about 14.1[Formula: see text]fb. Hence, these striking results are useful in the synthesis of superheavy element [Formula: see text].

Bayesian uncertainty quantification for synthesizing superheavy elements

To improve the theoretical prediction power for synthesizing superheavy elements beyond Og, a Bayesian uncertainty quantification method is employed to evaluate the uncertainty of the calculated evaporation residue cross sections (ERCS) for the first time. The key parameters of the dinuclear system model (DNS-sysu), such as the diffusion parameter a, the damping factor Ed, and the level-density parameter ratio af/an are systematically constrained by the Bayesian analysis of recent ERCS data. One intriguing behaviour is shown that the optimal incident energies (OIE) corresponding to the largest ERCS weakly depend on the fission process. We also find that these parameters are strongly correlated and the uncertainty propagation considering the parameters independently is not reasonable. The 2σ confidence level of posterior distributions for a=0.586−0.002+0.002 fm, Ed=25.65−3.41+3.43 MeV, and af/an=1.081−0.021+0.021 are obtained. Furthermore, the confidence levels of the ERCS and OIE for synthesizing Z = 119 via the reactions Cr54+243Am, Ti50+249Bk, and V51+248Cm are predicted. This work sets the stage for future analyses to explore the OIE and reaction systems for the synthesis of superheavy elements.

Coulomb interaction dependence of optimal energy to synthesize superheavy elements

The production of superheavy elements beyond Z = 118 remains unattained through both cold and hot fusion techniques, primarily due to inadequate fusion reaction optimization involving projectile–target combinations and energy. Past efforts employed various theories to optimize these combinations. In our current study, we have successfully identified optimal fusion energies for synthesizing superheavy elements, employing an advance statistical model and dinuclear system models. The establishment of optimal energy governing rule is achieved through a comprehensive examination of the Coulomb interaction parameter, enabling precise determination of the optimal energy for successful fusion reactions in synthesizing superheavy elements. The confidence level of predicting optimal energies using the present formula varies between 97% to 99%. The predicted optimal energy using the present formula for five fusion reactions such as 208Pb(50Ti,1n)257Rf, 208Pb(50Ti,2n)256Rf, 209Bi(50Ti,1n)258Db, 208Pb(58Fe,1n)265Hs, and 244Pu(48Ca,4n)288Fl were studied and are in good agreement with each other. Furthermore, we predicted the Optimal energies for fusion reactions leading to synthesize the superheavy element Z = 119 and 120. The presented empirical rule will certainly bring a revolution in the synthesis of superheavy elements.

The superheavy nuclei: Fusion-evaporation reactions

The synthesis of superheavy elements beyond the oganesson (Og, Z = 118) remains one of the actual topics in nuclear physics. For this purpose, the fusion reactions with projectiles heavier than 48Ca, which were successfully implied for the synthesis of the heaviest elements, and actinide targets have to be used. However, empirical knowledge on such reactions is almost absent. In this work, the experimental cross sections of the “hot”, “cold”, and 48Ca+actinide reactions were analyzed to reveal their differences in the three steps of the fusion-evaporation process. The evaporation residue cross sections represented as a function of the mean fissility parameter show the hitherto unnoticed difference between the “hot” and “cold” fusion reactions, which is in agreement with nuclear reaction dynamic studies. Based on the newly suggested systematics, the evaporation residue cross sections for the 50Ti, 51V, 54Cr, 58Fe and 64Ni-induced reactions with actinide targets were estimated within the two different empirical approaches.

Analysis of the shell effect of fission fragments in the quasi-fission process

The process in superheavy element synthesis in which two nuclei collide and fission before forming a compound nucleus is called quasi-fission. The dynamical model used in our calculations is highly reproducible in calculating the total kinetic energy (TKE) of actinide fission. However, there is a problem in the reproducibility of TKE of quasi-fission in the current calculations using the dynamical model. Our calculations show that the TKE of mass asymmetry is lower than the experimental data. The reason for this is that the shell effect of fission fragments is not considered. In this study, we attempted to reproduce mass-asymmetric quasi-fission with shell effects by using a dynamical model. The objective is to analyze the calculation results and follow the time evolution of the shape of the nucleus to deepen our understanding of the dynamics of quasi-fission.

Analysis of reaction dynamics considering MAD by Langevin equation

In heavy ion fusion and nucleon transfer reactions, which lead to the synthesis of superheavy elements, it is important to understand the reaction mechanisms. The fusion reaction mechanism is analyzed in the case of deformed target nuclei such as actinide target nuclei. We have analyzed the correlation between fission fragment mass and scattering angle (MAD) using the Langevin equation. Taking into account the effect of the collision direction between the projectile and deformed target nuclei, we present the analysis of the experimental data for the MAD of 32S+232Th.

Sequential fission and the influence of 208Pb closed shells on the dynamics of superheavy element synthesis reactions

Measured binary quasifission mass spectra in reactions with actinide nuclides show a large peak in yield near the doubly-magic 208Pb, generally attributed to enhanced binding energy causing a valley in the potential energy surface, which attracts quasifission trajectories. Measurements of binary quasifission mass spectra and cross-sections have been made for reactions of 50Ti with actinide nuclides from 232Th to 249Cf. Cross-sections have also been deduced for sequential fission (a projectile-like nucleus and two fragments from fission of the complementary target-like nucleus). Binary cross-sections fall from 70% of calculated capture cross-sections for 232Th to only 40% for 249Cf, with a compensating increase in sequential fission cross-sections. The data are consistent with the peak in yield near 208Pb originating largely from sequential fission of heavier fragments produced in more mass-asymmetric primary quasifission events. These are increasingly suppressed as the heavy quasifission fragment mass increases above 208Pb. The important role of sequential fission calls for re-interpretation of quasifission observables and dynamics in superheavy element synthesis reactions.

Colliding heavy nuclei take multiple identities on the path to fusion

The properties of superheavy elements probe extremes of physics and chemistry. They are synthesised at accelerator laboratories using nuclear fusion, where two atomic nuclei collide, stick together (capture), then with low probability evolve to a compact superheavy nucleus. The fundamental microscopic mechanisms controlling fusion are not fully understood, limiting predictive capability. Even capture, considered to be the simplest stage of fusion, is not matched by models. Here we show that collisions of 40Ca with 208Pb, experience an ‘explosion’ of mass and charge transfers between the nuclei before capture, with unexpectedly high probability and complexity. Ninety different partitions of the protons and neutrons between the projectile-like and target-like nuclei are observed. Since each is expected to have a different probability of fusion, the early stages of collisions may be crucial in superheavy element synthesis. Our interpretation challenges the current view of fusion, explains both the successes and failures of current capture models, and provides a framework for improved models.

Influence of «FLAT–TOP» of the resonant system of the DC-280 accelerator on the beam of charged particles

Experiments on the synthesis of superheavy elements (SHE) which were done at Flerov Laboratory of Nuclear Reactions (FLNR) measure that the probability of occurrence of one SHE event is ranged from one event per month to one event per week. Nowadays, Z = 118 (Oganesson) is the most used chemical element which is synthesized with 48Ca. The synthesis of new SHEs requires heavier bombarding particles: 50Ti, 54Cr, 58Fe, etc. In the experiments with heavier particles, the SHE isotope production cross section is expected to be lower than in the case of using 48Ca. It follows that it is necessary to increase the intensity of bombarding ion beams in order to collect experimental statistics in a reasonable time. Thus, for the synthesis of superheavy elements in the FLNR at the Joint Institute for Nuclear Research (JINR), the Factory of Superheavy Elements was created. The basic equipment of the SHE Factory is the DC-280 cyclotron complex. The accelerator provides high intensity of ion beams. As the intensity in the beam increases, the energy spread increases. That to minimize this process, the DC-280 cyclotron is equipped with an additional FLAT–TOP accelerating system.

Synthesis of superheavy elements

Synthesis of superheavy elements

Experimental investigation of the role of shell structure in quasifission mass distributions

Background: To understand superheavy element synthesis reactions, quantifying the role of quantum shells in quasifission dynamics is important. In reactions with actinide nuclides, a wide peak in the binary quasifission mass yield is seen, centered close to the $^{208}\mathrm{Pb}$ mass. It is generally attributed to the $^{208}\mathrm{Pb}$ spherical closed shells causing a valley in the potential-energy surface, attracting flux to these mass splits. However, an early experiment studying $^{48}\mathrm{Ca}, ^{50}\mathrm{Ti}+^{238}\mathrm{U}$ reactions showed strong evidence that sequential fission plays an important role in generating the observed peak. These conflicting interpretations have not been resolved up to now.Purpose: This work aims to measure quasifission mass spectra for reactions with nuclei lighter than $^{208}\mathrm{Pb}$, having negligible sequential fission, to search for systematic features correlated with the proton shells known to affect low-energy fission mass distributions of the same actinide elements.Methods: Systematic measurements have been made at energies near and below the capture barriers (where quasifission is most prominent) of mass-angle distributions for fission following collisions of $^{48}\mathrm{Ti}$ projectiles with even-even nuclides from $^{154}\mathrm{Sm}$ to $^{200}\mathrm{Hg}$. Mean excitation energies above the ground-states ranged from 51 to 33 MeV, respectively.Results: With increasing compound nucleus atomic number ${\mathrm{Z}}_{CN}$, a rapid transition occurs from fission having characteristics of fusion-fission to fast quasifission. The heaviest reactions form $^{240}\mathrm{Cf}, ^{244}\mathrm{Fm}$, and $^{248}\mathrm{No}$. Low-energy fission of neighboring isotopes is mass asymmetric, correlated with proton number $Z=56$. However, peak quasifission yields are at mass-symmetry for all reactions. There appears to be a very small ($\ensuremath{\approx}3$%) systematic excess of yield correlated with $Z=56$, however this is at the limit of sensitivity of the experiment.Conclusions: No significant ($>3%$) systematic features are seen in the quasifission mass spectra that can be unambiguously identified as resulting from shells. This small influence may result from attenuation of shell effects due to the excitation energy introduced, even in these near-barrier reactions giving low excitation energies typical of superheavy element synthesis reactions.

Sequential fission and the influence of 208Pb closed shells on the dynamics of superheavy element synthesis reactions

Measured binary quasifission mass spectra in reactions with actinide nuclides show a large peak in yield near the doubly-magic 208Pb. This has generally been attributed to the enhanced binding energy of 208Pb causing a valley in the potential energy surface, attracting quasifission trajectories. To investigate this interpretation, binary quasifission mass spectra and cross-sections have been measured at near-barrier energies for reactions of 50Ti with actinide nuclides from 238U to 249Cf. Cross-sections have also been deduced for sequential fission (a projectile-like nucleus and two fragments from fission of the complementary target-like nucleus). Binary cross-sections fall from ∼70% of calculated capture cross-sections for 238U to only ∼40% for 249Cf, with a compensating increase in sequential fission cross-sections. The data are consistent with the 208Pb peak originating largely from sequential fission of heavier fragments produced in more mass-asymmetric primary quasifission events. These are increasingly suppressed as the heavy quasifission fragment mass increases above 208Pb. The important role of sequential fission calls for re-interpretation of quasifission characteristics and dynamics in superheavy element synthesis reactions.

Predictions for the synthesis of the Z=120 superheavy element

The possible stable and radioactive beam-induced hot fusion reactions for the production of new superheavy element (SHE) $Z=120$ are investigated within the dinuclear system model. Our investigation shows that the reaction $^{45}\mathrm{Sc}+^{252}\mathrm{Es}$ has a relatively large evaporation residue cross-section (ERCS) for the synthesis of SHE $Z=120$ due to its slightly larger mass asymmetry. In addition, we analyzed the effects of fission barrier and neutron separation energy of superheavy nuclei on ERCS. To synthesize the double-magic $Z=120$ and $N=184$ nucleus predicted by the relativistic mean-field model, some radioactive beam-induced fusion reactions, which can be performed in available experimental equipment, for producing superheavy nucleus $^{304}120$ in neutron evaporation channels are investigated systematically. We find that the hot fusion reaction $^{50}\mathrm{Ca}+^{257}\mathrm{Fm}$ in the $3n$ evaporation channel is optimal for synthesizing the superheavy nucleus $^{304}120$. We hope these predictions will shed new light timely for the recent experiments on the synthesis of $Z=120$ superheavy element and the search for superheavy stability islands.

Development of Micro-Pattern Gaseous Detectors for Nuclear Reaction Studies

One of the frontiers of today’s nuclear physics research is the synthesis of Super Heavy Elements (SHE). Fusion-fission dynamics, namely the competition between quasi fission and fusion is one of the key challenges to optimize the SHE. To have an insight into the dynamics, one requires the study of fission fragment mass and angular distribution near barrier energies for heavy-ion induced fission reactions. Recent successful installation of linear accelerators in India offers a unique opportunity to study the dynamics of nuclear reactions and formation process of SHE. For the effective utilization of these current, as well as upcoming facilities, development of novel detectors to study reaction dynamics, formation process of SHE with heavier projectiles and higher beam energies is needed. Gaseous detectors have undergone a rapid improvement in terms of spatial, temporal and energy resolution, rate capability, radiation hardness, ion feedback etc., ushering in a new genre of micro-structured devices based on semi-conductor technology, commonly known as Micro-Pattern Gaseous Detectors (MPGDs). Although many of the MPGD structures were primarily developed for high-rate tracking of charged particles in high energy physics experiments, stability of operation, simplicity of construction and relatively low cost make these detectors suitable for other applications, such as low-energy nuclear physics experiments. The present activities encompass a detailed evaluation of the operational conditions of Micromesh-Multi Wire and THGEM-Multi Wire hybrid detector operated in low-pressure isobutane gas with a view to optimizing their use in the detection of charged particles and fission fragments.

Synthesis of superheavy elements using krypton and argon beams

Synthesis of superheavy elements using krypton and argon beams

Formation of large chunk of nuclear matter in heavy-ion collisions

In terrestrial laboratory with existing accelerators, the maximum multinucleon system produced so far is limited to that with total nucleon number being less than the sum of two colliding nuclei. Such situation may hinder our studies on the properties of nuclear many-body system. Here a way of producing large multinucleon system via multi-nucleus collision device Collider Plus in terrestrial laboratory is proposed. It is shown that large chunk of nucleonic matter can be produced through nuclear ternary fusion reactions at lower beam energies and also large block of dense matter can be formed via ternary collisions of heavy nuclei at intermediate energies. These investigations may shed lights on the studies of the synthesis of superheavy elements and the properties of bulk superdense nuclear matter.

Systematic study of probable target-projectile combinations for the synthesis of Z = 120 isotopes using the Skyrme energy density formalism

The synthesis of superheavy elements is an interesting field of research for both theoretical as well as experimental physicists. Till now superheavy element from Z=104 to 118 has been synthesized in various laboratories using cold and hot fusion reactions. Recent predictions of various theoretical models state that Z=120 and N=184 seems most probable doubly magic pair in the island of stability. Hence, we aim to the predict most probable target-projectile combinations of 300,302,304120 superheavy nuclei, so that relevant inputs may be imparted for future synthesis of superheavy nuclei. The target-projectile combinations are taken in reference to the minima's of the fragmentation potential calculated using the Quantum Mechanical Fragmentation Theory (QMFT). In addition, the target-projectile combinations from literature are also considered for which attempts were made for the synthesis of Z=120. The barrier height (VB) of the considered target-projectile combinations are calculated using the spherical and deformed choices of decay fragments. The percentage change in the barrier height ΔVB is explored for the hot and cold fusion approaches. The nuclear interaction potential is obtained within the Skyrme energy density formalism (SEDF) using the GSkI force parameters. For the feasible target-projectile (t-p) combinations, the capture cross-sections of these three isotopes 300,302,304120 are calculated using ℓ-summed Wong model and their comparative analysis is worked out. The probability of formation of compound nucleus (PCN) is determined using the energy dependent function. Among the thirty-six considered target-projectile combinations, the Ti-based reactions with Cf targets and also Cr-based reactions with Cm targets are identified as most suitable combinations for the synthesis of the superheavy element with Z=120. For 300120 isotope are 48Ti+252Cf, 50Ti+250Cf, 50Cr+250Cm, 52Cr+248Cm; whereas 50Ti+252Cf, 54Cr+248Cm, and 54Cr+250Cm form most probable target-projectile pair respectively, for 302120 and 304120 superheavy nuclei.

Superconducting Linac Booster for Super-Heavy Element Experiments at RIKEN Radioactive Isotope Beam Factory

The Rikagaku Kenkyūjo (RIKEN) heavy-ion linac was upgraded by introducing a new super-conducting linac-booster to advance the super-heavy elements synthesis program beyond nihonium at the RIKEN Radioactive Isotope Beam Factory (RIBF). The total acceleration voltage was upgraded from 25 MV with 12 room temperature drift-tube-linacs (DTLs) to 39 MV by introducing a superconducting linac booster, SRILAC. The upgrade of the beam intensity is realized by a newly constructed superconducting electron-cyclotron resonance ion source (SC-ECRIS). The construction of SRILAC and the SC-ECRIS started in FY2017. After the hardware installation and commissioning, the first beam acceleration test was successfully conducted at the end of FY2019, and user beam service was started in FY2020. This article provides an overview of the upgrade and its present performance.

New Coulomb barrier scaling law with reference to the synthesis of superheavy elements

The synthesis of superheavy elements based on fusion reactions and multinucleon transfer reactions is sensitive to the reaction energies, where the Coulomb barrier plays a crucial role as it must be overcome for the projectile and target to contact each other. The Coulomb barrier cannot be measured directly, and the synthesis of superheavy elements is sensitive to it. In this study, we systematically extract the barrier information from the experimental fusion excitation functions by the empirical cross section formula, which is based on a single-Gaussian distribution of fusion barrier heights. A total of 403 sets of experimental data are fitted, among which 243 sets have good results with ${\ensuremath{\chi}}^{2}/pt$ less than one. The extracted fusion barrier is a dynamical barrier, which includes the overall effect of coupled channels. Different from the prediction of the WKJ formula, the new scaling law proposed in this work is almost identical to the CW76 Coulomb barrier at the $z=170--300$ region and reproduces well the centroid barrier extracted from quasielastic scattering. The comparison to the other 14 bare potential models and exploration of the very large $z$ region is also discussed. It is also remarkable to find that the predictions of the DP2015 potential, including of the contributions of the macroscopic and shell correction terms, are highly consistent with the extracted results in this work and the CW76 potential. The numerical results demonstrated that the dynamical fusion barrier and the centroid barrier extracted from the quasielastic reaction (the reaction threshold) could be the same physical quantity for superheavy reactions. This study could provide important references for the synthesis of superheavy nuclei based on fusion reactions and very heavy multinucleon transfer reactions.

Investigations on 48Ca and 58Fe-induced heavy ion fusion reactions

In this paper, we have studied all possible [Formula: see text] and [Formula: see text]-induced fusion reactions for the synthesis of superheavy nuclei [Formula: see text]. The semi-empirical formula for fusion barriers of [Formula: see text] and [Formula: see text] is constructed. Fusion and evaporation residue cross-sections are studied using advance statistical model (ASM). The fusion and evaporation residue cross-sections of this work are compared with that of experiments. We have also predicted suitable targets and production cross-sections for the synthesis of superheavy elements using the [Formula: see text] and [Formula: see text]-induced fusion reactions. The [Formula: see text]-induced fusion reactions can be used to synthesize superheavy elements [Formula: see text] and 124 using the targets [Formula: see text]Cm, [Formula: see text]Bk and [Formula: see text]Cf have half-lives greater than one year and produce the cross-sections in terms of pb.