Evaporation Residue Cross Sections 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].

Possibility to synthesize $Z = 119$ superheavy nuclei with $Z>$ 20 projectiles

Abstract We employed the dinuclear system (DNS) model combined with statistical model to calculate the evaporation residue cross sections for the reaction systems $^{48}$Ca + $^{243}$Am, $^{48}$Ca + $^{248}$Cm, and $^{48}$Ca + $^{249}$Bk. The theoretical results successfully reproduced the experimental trends in the 3$n$ and 4$n$ evaporation channels of these reaction systems. In order to synthesize the new element $Z = 119$, we predicted the evaporation residue cross sections for three reaction systems ($^{54}$Cr + $^{243}$Am, $^{51}$V + $^{248}$Cm, and $^{50}$Ti + $^{249}$Bk) to select the most promising projectile-target combinations. We also noted that the maximum cross sections predicted by our model and other methods appear to be below the detection limits of current experimental facilities, given the projectile-target combinations feasible under current experimental conditions. Therefore, synthesizing superheavy nuclei with $Z = 119$ will require improvements in beam intensity, detection techniques, and effective separation methods.

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.

A study on the synthesis of superheavy element Mc (Z = 115) using lead, bismuth and actinide targets

The evaporation residue cross sections in synthesizing isotopes of superheavy element Mc (Z = 115) by the hot fusion reactions 48Ca+241,243Am→289,291Mc, 45Sc+240,242,244Pu→285,287,289Mc, 50Ti+236,237Np→286,287Mc, 51V+238U→289Mc, 36S+253Es→289Mc, 46K+248Cm→294Mc, and by the cold fusion reactions 78As+208Pb→286Mc, 76Ge+209Bi→285Mc have been systematically investigated using the phenomenological model for production cross section. We have predicted the most effective projectile-target combinations for synthesizing Mc isotopes among these reactions. Our result shows that the 3n- channel cross section is larger for the reaction 48Ca+243Am→291Mc, and the 4n- channel cross section is larger for the reaction 46K+248Cm→294Mc. This study also examines the effect of the use of mass values and shell corrections by the Möller and Warsaw groups. Using our predicted combinations and the cross section values at a range of excitation energies, we hope these isotopes of Mc can be synthesized in near-future experiments.

70Zn-induced fusion reactions for synthesis of superheavy element Z=120

In this work, we delved into the intriguing realm of nuclear physics by investigating fusion reactions initiated by [Formula: see text]Zn projectiles colliding with various stable isotopes of thorium nuclei, including [Formula: see text]Th. Our primary objective was the synthesis of the superheavy element [Formula: see text]. To achieve this, we employed an advanced statistical model to evaluate the evaporation residue cross-sections. Remarkably, we observed that the fusion reaction between [Formula: see text]Zn and [Formula: see text]Th exhibited the highest evaporation residue cross-sections, reaching a peak value. Furthermore, the 3n channel within this fusion reaction yielded substantially larger evaporation cross-sections, with a notable value of 0.89 picobarns. The predicted cross-sections fall within the measurable range, making them highly valuable for experimental endeavors aimed at synthesizing the superheavy element [Formula: see text]. This research not only contributes to our understanding of nuclear reactions but also holds promise for expanding our knowledge of the heaviest elements in the periodic table, potentially opening new frontiers in nuclear science.

Observation of suppression of heavy-ion fusion by slow quasifission

The formation of superheavy elements (SHEs) by nuclear fusion can be conceptually divided into two steps: capture, and compound nucleus formation. Once captured, the two nuclei may reseparate before fusing to form a compact compound nucleus. This outcome is called quasifission. Fusion-fission, in many cases, leads to reactions outcomes inseparable from quasifission. Evaporation residue (ER) measurements are therefore the most reliable, direct experimental signature of fusion. ER cross section measurements forming the same compound nucleus, 220Th, using 16O, 40Ar, 48Ca, 82Se and 124Sn-induced reactions [1–4] revealed [1] that fusion was severely suppressed for the more symmetric reactions relative to the 16O-induced reaction. Here two new reactions forming 220Th using 28Si, 34S projectiles provide conclusive evidence that the ER cross section is exponentially suppressed as a function of ZpZt. The fission characteristics show no mass-angle correlation, demonstrating that here ER cross sections are suppressed by slow quasifission.

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.

Entrance channel dependence of quasi fission in reactions leading to 206Po compound nucleus

The evaporation residue (ER) cross sections for the reaction F19+187Re→206Po⁎ are measured, in the excitation energy range of 86.1 to 118.4 MeV. The measured cross sections are compared with that of 30Si + 176Yb reaction populating the same compound nucleus. Theoretical calculations are performed using the coupled - channels calculations for the capture cross sections and statistical model calculations for the ER cross sections. The dependence of quasi fission on entrance channel parameters such as charge product (Z1Z2), mass asymmetry (α), target deformation (β2) and effective fissility (χeff) are studied.

Evaporation residue cross-section measurements for 30Si+142Ce system

Evaporation residue (ER) cross-sections were measured for 30Si+142Ce reaction at laboratory energies in the range of 105 - 132 MeV using the HYbrid Recoil mass Analyzer (HYRA) at IUAC, New Delhi. The transmission efficiency of the HYRA was estimated using the calibration reaction 28Si+142Ce. Sub-barrier fusion enhancement was observed when compared with the one-dimensional barrier penetration model predictions for the present system. To explore the phenomena responsible for sub-barrier fusion enhancement, coupled-channels calculations were performed using the CCFULL code. The effect of couplings and the role of positive Q-value neutron transfer (PQNT) channels on sub-barrier fusion cross-sections were investigated. Coupled-channels calculations were able to reproduce the data by including the coupling in both projectile and target nucleus along with two neutron-transfer channels having positive Q-value. The measured ER cross-sections were compared with the nearby systems to explore the role of deformation of the colliding nuclei.

Evaporation residue cross sections of superheavy nuclei based on optimized nuclear data* *Supported by the National Natural Science Foundation of China (12175170, 11675066)

This study proposes an optimized method for estimating atomic nucleus masses by combining the finite-range droplet model (FRDM) with the support vector machine algorithm. The optimization process significantly improves the accuracy of the FRDM by reducing the root mean square error from 0.606 to 0.253 MeV. The optimized mass data obtained from this method are then used to calculate the evaporation residue cross-sections (ERCSs) for fusion-evaporation reactions, employing the di-nuclear system model. The experimental results for the 48Ca+238U reaction are relatively well reproduced using these optimized mass data. Additionally, the study investigates the impact of mass uncertainties on fusion and survival probabilities. By considering the mass uncertainties, the ERCSs for new elements 119 and 120 are predicted based on the obtained optimized mass data.

Investigation on the Quasifission hindrance to synthesis 298Og

Formation of a compound nucleus and production of its evaporation residue are hindered by quasi-fission process. It reduces the evaporation residue cross section since it takes place before the target and projectile combines to form a composite nucleus. We study the quasifission barriers (Bqf) for 14 fusion reactions in the formation of superheavy element 298Og within the framework of the di-nuclear system model. In particular, the influence of entrance channel parameters on quasifission barriers has been investigated. We notice that the quasifission barriers decreases with an increase in angular momentum and fusion barrier height. We constructed semi-empirical formulae for Bqf as a function of mean fissility. The fusion reaction 48Ca+250Cf poses larger Bqf. The larger evaporation cross section is observed for this fusion reaction for 3n evaporation channel with the cross-section of 0.81pb. Similarly, a smaller evaporation cross-section of about 0.033pb is observed for 51Cr+247Pu fusion reaction for 4n evaporation channel with both projectile and target being deformed, unlike to the previous reaction with spherical projectile and deformed target.

Correlation of intrinsic fusion barriers and evaporation residue cross-sections of SHEs

Correlation of intrinsic fusion barriers and evaporation residue cross-sections of SHEs

Systematic study of prescission neutron multiplicity: Revealing the role of entrance channel magicity

The prescission neutron multiplicities (νpre) are studied for a systematic understanding of the influence of entrance-channel shell closure in fusion-fission dynamics. The existing νpre data are analyzed for reactions with a wide variety of target and projectile combinations. For completeness, the measured νpre data for the fusion-fission reactions with the doubly closed shell 16O projectile on the targets having either proton (204,206Pb) or both proton and neutron (208Pb) shell closure is reanalyzed. Although the measured νpre for 224Th disagree with the available data reported by Rossner et al. (1992) [1], our results are found to be more consistent and follow a systematic trend as described in this letter. Theoretical analysis is performed within the standard statistical model framework, where dissipation strength is used as a tunable parameter. It is observed that irrespective of the compound nuclear excitation energy, the entrance channel magicity imparts an intriguing impact on the dissipation strength. A similar entrance channel effect in the evaporation residue cross-section is also demonstrated. In conclusion, the present analysis establishes an entanglement of the exit channel observables with the entrance channel shell closure. It contradicts the hypothesis of complete equilibrium in compound nuclear reactions.

Lithium–lithium fusion evaporation research

AbstractIn this study we have explored6Li + 7Li fusion evaporation reactions cross sections dependencies on both nuclear level density and various spin combination effects. The reaction cross section was calculated in the energy range of 0.1–16 MeV projectile of6Li on the fixed target of7Li. The excited compound nucleus (13C) can decay into various channels, and its decay rate in any given channel is proportional to the available phase space, i.e., the corresponding level density of it which is explained in the present study. In the present study, LISE++, PACE4, NRV and GEMINI codes were used to determine cross section of evaporation residues cross sections of13C.

Examination of promising reactions with Am241 and Cm244 targets for the synthesis of new superheavy elements within the dinuclear system model with a dynamical potential energy surface

Two actinide isotopes, $^{241}$Am and $^{244}$Cm, produced and chemically purified by the HFIR/REDC complex at ORNL are candidates for target materials of heavy-ion fusion reaction experiments for the synthesis of new superheavy elements (SHEs) with $Z>118$. In the framework of the dinuclear system model with a dynamical potential energy surface (DNS-DyPES model), we systematically study the $^{48}$Ca-induced reactions that have been applied to synthesize SHEs with $Z=112$--118, as well as the hot-fusion reactions with $^{241}$Am and $^{244}$Cm as targets which are promising for synthesizing new SHEs with $Z=119$--122. Detailed results including the maximal evaporation residue cross section and the optimal incident energy for each reaction are presented and discussed.

Facets of reaction mechanism in 6Li+181Ta system

More focused investigations are required to better understand the different modes of fusion phenomena in weakly bound projectiles. In order to comprehend the reaction mechanism of weakly bound projectiles, a new measurement of the evaporation residue cross sections from the 6Li-induced reaction on 181Ta in the 4.5–7.1 MeV/nucleon energy range has been reported in this article. The γ-ray spectrometry has been employed to identify the 183m,g Os, 182Os, 183Re, and 183,182m2,180Ta residues produced in the reaction via different evaporation channels. The EMPIRE-3.2.2 code, which houses both the equilibrium and pre-equilibrium models in its framework, and PACE4 have been tasked to analyze the measured excitation functions. Out of the two, EMPIRE-3.2.2 demonstrates better agreement with the data. A systematic analysis of the measured data and theoretical background indicates that the complete and incomplete fusion of 6Li contribute to the residual cross sections. Thus, the strength of the partial fusion has been inferred. Further, the neutron transfer channels have been found to contribute significantly to the reaction dynamics; hence they are investigated using the coupled reaction channel calculations and discussed in detail. The isomeric cross section ratio obtained from the measured residual cross sections of the isomeric pair of 183Os highlights the significance of angular momentum and relative spins of the ground and isomeric states as a function of projectile incident energy.

Theoretical study of superheavy elements 294,297Og using different versions of proximity potential

Formation of superheavy nuclei 294,297Og is studied via calculation of evaporation residue cross section. We investigated the influence of nuclear potential on the evaporation residue cross section using nine versions of proximity potential as Prox77, Prox88, BW91, Bass73, Bass77, Denisov, CW76, GP77 and Guo2013. Calculations are performed for 65 projectile-target combinations with convenient half lives. It is found that the combinations 46Ca+248Cf and 48Ca+249Cf are most favorable for the synthesis of the elements 294,297Og with evaporation cross sections 1395 and 279 fb for the 3n channel in proximity potential Guo2013. The lowest value of evaporation cross section is obtained for Bass73 potential. We have also examined the agreement of the results obtained from different potentials with the experimental data for the systems 48Ca+245Cm, 48Ca+248Cm, and 48Ca+249Bk. The results obtained from potentials Guo2013, GP77 and CW76 show better agreement with the experimental results in comparison with other potentials.

Systematic analysis of the decay of Fl*287,288,290,292 formed in the complete fusion reactions Pu239,240,242,244+Ca48 including Skyrme forces

The fusion evaporation residue cross sections for the decay of the compound nuclear system $^{287,288,290,292}\mathrm{Fl}^{*}$ via $2n$- to $5n$-decay channels, synthesized in $^{239,240,242,244}\mathrm{Pu}+^{48}\mathrm{Ca}$, are studied using the dynamical cluster-decay model (DCM), including quadrupole deformations ${\ensuremath{\beta}}_{2i}$ for compact hot orientations ${\ensuremath{\theta}}_{i}$ at various excitation energies ${E}^{*}=32.5$ to 52.6 MeV. For the nucleus-nucleus interaction potentials, we have employed the Skyrme energy density functional based on the semiclassical extended Thomas-Fermi approach under frozen density approximation. Here, within the DCM, the Skyrme forces used are SLy4, ${\mathrm{SkM}}^{*}$, and, KDE0(v1). The DCM makes use of a single parameter, the neck-length parameter $\mathrm{\ensuremath{\Delta}}R$ that takes different values for different processes at a given temperature and provides an excellent fit to the measured data, independently of the choice of Skyrme force used. We make predictions of probable fusion-fission and quasifission mass regions of fragments and then calculate the evaporation residue cross sections ${\ensuremath{\sigma}}_{\mathrm{ER}}$ for experimentally unobserved neutron channels. Further, the product ${P}_{\mathrm{CN}}{P}_{\mathrm{surv}}$ of compound nucleus (CN) fusion probability ${P}_{\mathrm{CN}}$ and survival probability ${P}_{\mathrm{surv}}$ is calculated to determine the reduced evaporation residue cross section ${\ensuremath{\sigma}}_{\mathrm{ER}}/{\ensuremath{\sigma}}_{\mathrm{fusion}}$, denoted as ${\ensuremath{\sigma}}_{\mathrm{ER}}^{\mathrm{reduced}}$, and we have seen that ${P}_{\mathrm{surv}}$ is the main dominant factor in the product ${P}_{\mathrm{CN}}{P}_{\mathrm{surv}}$. To this end, we have analyzed the effects of mass asymmetry and isospin effect of target nucleus on the ${\ensuremath{\sigma}}_{\mathrm{ER}}$ and have found that the ${\ensuremath{\sigma}}_{\mathrm{ER}}$ for the production of superheavy element ${\mathrm{Fl}}^{*}$ increases slowly with increasing neutron number of the target nucleus. We have also searched for all possible target-projectile combinations forming the hot compound nucleus ${\mathrm{Fl}}^{*}$ at the excitation energy ${E}^{*}$ for compact-hot configurations and have also calculated the fusion evaporation residue cross sections for the proposed new reactions synthesizing Fl.

Survival probability of compound nuclei in heavy-ion fusion reaction

We have developed an empirical formula to calculate the survival probability of superheavy nuclei by analyzing about 95 fusion experiments, which were classified into four categories based on the deformation parameters of a projectile–target system. Every category is analyzed using ten different entrance channel parameters; one of these displays the smoothest variation. That channel is Z 2/A, where Z and A are the atomic number and mass number, respectively. Further, the predicted empirical relation is improved by the inclusion of the fission barrier, separation energy, level density parameter, center of mass energy, and fusion barrier height for the Z 2/A term. Furthermore, the evaporation residue cross-section is maximum at a certain beam energy, called the optimal energy. Thus, finding the survival probability at the optimal energy is important in the synthesis of a superheavy nucleus. We have developed an empirical formula for the survival probability at the optimal energy to facilitate future superheavy nucleus synthesis.

Rules of thumb for synthesizing superheavy elements

Synthesizing any elements in the eighth period using either cold or hot fusion reactions remains a big challenge to date. The quasifission mechanism restricts complete fusion to an indeterminably low evaporation residue (ER) cross-section for superheavy nuclei. The entrance channel parameters of the heavy-ion reaction, the fission barrier of the compound nucleus, the deformation parameters of the projectile and target nuclei, and the kinetic energy of the projectile are mainly responsible for governing the scale of the quasifission. The role of these factors has been examined explicitly by the experimental ER cross-sections. Thorough comparisons lead us to infer that the entrance channel criteria contribute to a much lower extent than the deformation parameters do. The effect of deformation can be categorized into four rules as validated by all the reactions used except one Uue. The null result from this reaction is explained by the improper choice of the projectile energy, as shown theoretically by means of a statistical model approach, which is valid for a system having a large nucleon number so as to intrinsically have a high density of excited states. The optimal selection of the beam energy sets another rule. Therefore, these five rules can be treated as the rules of thumb for synthesizing the superheavy elements. Application of the first four rules can enable us primarily to spot a suitable reaction, and finally, exploitation of the fifth rule chooses the most appropriate reaction at a preferable excited energy to achieve the highest ER cross-section for a superheavy element.