Possibilities for the synthesis of superheavy element Z=121 in fusion reactions

Based on the dinuclear system model,the calculated evaporation residue cross sections matched well with the current experimental results.The synthesis of superheavy elements Z=121 was systematically studied through combinations of stable projectiles with Z=21-30 and targets with half-lives exceeding 50 d.The influence of mass asymmetry and isotopic dependence on the projectile and target nuclei was investigated in detail.The reactions^(254)Es(^(46)Ti,3n)^(297)121 and^(252)Es(^(46)Ti,3n)^(295)121 were found to be experimentally feasible for synthesizing superheavy element Z=121,with maximal evaporation residue cross sections of 6.619 and 4.123 fb at 219.9 and 223.9 MeV,respectively.

Systematic study on heavy-particle radioactivity of superheavy nuclei ^(297–300)119

In the current study,we examined every possible cluster-daughter combination in the heavy-particle decay of isotopes ^(297-300)119 and computed the decay half-lives using the modified generalized liquid drop model(MGLDM)with the preformation factor depending on the disintegration energy.The predicted half-life of every heavy cluster(Z_(C)≥32)was within the experimentally observable limits.These results aligned with the predictions of Poenaru et al.[Phys.Rev.Lett.107,062503(2011)]that superheavy nuclei(SHN)with Z>110 will release heavy particles with a penetrability comparable to or greater than theα-decay.The half-lives predicted using the MGLDM for clusters^(89)Rb,^(91)Rb,and^(92)Rb from parents^(297)119,^(299)119,and^(300)119,respectively,agreed with the predictions of Poenaru et al.[Eur.Phys.J.A 54,14(2018)].It was found that the isotopes of heavy clusters Kr,Rb,Sr,Pa,In,and Cd had half-lives comparable to theαhalf-life;and isotopes of clusters I,Xe,and Cs had the minimum half-life(10^(-14)s).These observations revealed the role of the shell closure(Z=82,N=82,and N=126)of the cluster and daughter nuclei in heavy-cluster radioactivity.We predicted that isotope ^(297,299)119 decayed by 4αdecay chains and isotope^(300)119 decayed by 6αdecay chains,while^(298)119 decayed by continuousαdecay chains.The predicted half-lives and modes of decay of the nuclei in the decay chains of^(297-300)119 agreed with the experimental data,proving the reliability of our calculations.The present study determined the most favorable heavy-cluster emissions from these nuclei and provided suitable projectile-target combinations for their synthesis.

Random forest-based prediction of decay modes and half-lives of superheavy nuclei

Information on the decay process of nuclides in the superheavy region is critical in investigating new elements beyond oganesson and the island of stability.This paper presents the application of a random forest algorithm to examine the competition among different decay modes in the superheavy region,includingα decay,β^(-)decay,β^(+)decay,electron capture and spontaneous fission.The observed half-lives and dominant decay mode are well reproduced.The dominant decay mode of 96.9%of the nuclei beyond ^(212) Po is correctly obtained.Further,α decay is predicted to be the dominant decay mode for isotopes in new elements Z=119-122,except for spontaneous fission in certain even–even elements owing to the increased Coulomb repulsion and odd–even effect.The predicted half-lives demonstrate the existence of a long-lived spontaneous fission island southwest of ^(298) Fl caused by the competition between the fission barrier and Coulomb repulsion.A better understanding of spontaneous fission,particularly beyond ^(286)Fl,is crucial in the search for new elements and the island of stability.

Influence of the shell effects on evaporation residue cross section of superheavy nuclei

In order to study the influence of the shell effects on the formation and fission of superheavy elements, we applied multidimensional Langevin equations. The evaporation residue cross sections have been calculated for 3n, 4n, and 5n evaporation channels using three(K = 0)-and four(K ≠ 0)-dimensional Langevin equations. Calculations were done for ^(48)Ca + ^(238)U and ^(48)Ca + ^(244)Pu hot fusion reactions with 3n, An evaporation channels and ^(70)Zn+ ^(208)Pb, and ^(54)Cr + ^(209)Bi cold fusion reactions with In and 2n evaporation channels. The calculations were performed for An and 5n evaporation channels of the ^(26)Mg+ ^(238)U reaction, as well. Our results show that with increasing dimension of Langevin equations the residue cross section increases, whereas the fission cross section decreases. The obtained results with four-dimensional Langevin and considering shell effects are in better agreement with experimental data in comparison with three-and four-dimensional Langevin equations without shell effects.

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

The fusion dynamics of the formation of super-heavy nuclei were investigated thoroughly within the din-uclear system model.The Monte Carlo approach was implemented in the nucleon transfer process to include 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 were calculated and compared with the available data from Dubna.The evaporation residue excitation functions in the channels of pure neutrons and charged particles were systematically analyzed.The combinations of 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 were calculated to produce the superheavy elements with Z¼119?122.We obtained that the production cross sections sensitively depend on the neutron richness of the reaction system.The structure of the evaporation residue excitation function is related to the neutron separation energy and fission barrier of the compound nucleus.

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

Abstract 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 than30 days for producing SHN^(264)Db,^(265)Db,^(267)Sg,^(268)Bh,268Sg,^(269)Bh,^(271)Hs,^(271)Mt,^(272)Hs,^(272)Mt,^(273)Mt,^(274)Ds,275Ds,^(275)Rg,^(276)Ds,^(276)Rg,^(277)Rg,^(278)Cn,^(279)Cn,and^(280)Cn are examined.Further,the optimal combinations and incident energies for synthesizing these nuclei are predicted.Most of the cross sections for production of SHNare larger than 10 pb;therefore,the process can be carried out with the available experimental equipment.

Systematic Study on Alpha Decay Half-Lives of Superheavy Nuclei

The α-decay half-lives of a set of superheavy nuclear isotope chain from Z = 105 to 120 have been analyzed systematically within the WKB method, and some nuclear structure features are found. The decay barriers have been determined in the quasi-molecular shape path within the Generalized Liquid Drop Model （GLDM） including the proximity effects between nucleons in a neck and the mass and charge asymmetry. The results are in reasonable agreement with the published experimental data for the alpha decay half-llves of isotopes of charge 112, 114, and 116, of the element 294118 and of some decay products. A comparison of present calculations with the results by the DDM3Y effective interaction and by the Viola-Seaborg-Sobiczewski （VSS） formulae is also made. The experimental a decay half lives all stand in between the GLDM calculations and VSS formula results. This demonstrates the possibility of these models to provide reasonable estimates for the half-lives of nuclear decays by a emissions for the domain of SHN. The half-lives of these new nuclei are thus well tested from the reasonable consistence of the macroscopic, the microscopic, the empirical formulae and the experimental data. This also shows that the present data of SHN themselves are consistent. It could suggest that the present experimental claims on the existence of new elements Z =110 - 118 are reliable. It is expected that greater deviations of a few SHN between the data and the model may be eliminated by further improvements on the precision of the measurements.

Ground State Properties of Superheavy Nuclei in Macroscopic-Microscopic Model

The ground state properties of superheavy nuclei are systematically calculated by the macroscopic-microscopic (MM) model with the Nilsson potential.The calculations well produced the ground state binding energies,α-decay energies,and half lives of superheavy nuclei.The calculated results are systematically compared with availableexperimental data.The calculated results are also compared with theoretical results from other MM models and fromrelativistic mean-field model.The calculations and comparisons show that the MM model is reliable in superheavy regionand that the MM model results are not very sensitive to the choice of microscopic single-particle potential.

On Q Values and Other Energy Parameters for Superheavy Element Synthesis

Q value and optimal exciting energy of hypothetical superheavy nuclei in cold fusion reaction are calculated with relativistic mean field model and semiemperical shell model mass equation (SSME) and the validity of the two models is tested. To give useful references for the experiments in the superheavy nuclei synthesized in cold fusion reactions,the Q value, fusion barrier and optimal exciting energy for the possible target plus projectile combinations suggested by Gupta et al. are calculated and the most possible target plus projectile combinations are pointed out according to our calculations.

Statistical Behaviors of Quantum Spectra in Superheavy Nuclei

From the point of view of the interplay between order and chaos, the most regular single-particle motion of neutrons has been found in the superheavy system with and based on the Skyrme–Hartree–Fock model and in the system with and based on the relativistic mean-field model. It has been shown that the statistical analysis of spectra can give valuable information about the stability of suprheavy systems. In addition it may yield deep insight into the single-particle motion in the mean field formed by the superheavy system.

The Role of Potential Structure in Excitation Functions of Synthesizing Superheavy Nuclei

The excitation functions of two very similar reaction channels, 58Fe＋ 208pb→ 265Hs ＋ 1n and 58Fe＋ 209Bi → 266Mt ＋1n are studied in the framework of the dinuclear system conception. The fusion probabilities are found to be strongly subject to the structure of the driving potential. Usually the fusion probability is hindered by a barrier from the injection channel towards the compound nuclear configuration. The barrier towards the mass symmetrical direction, however, also plays an important role for the fusion probability, because the barrier hinders the quasi-fission, and therefore helps fusion.

Antiproton Production with a Fixed Target and Search for Superheavy Particles at the LHC

A proposal for an experiment to measure the cross section of antiproton production in a proton-nuclear collision in a kinematically forbidden region for nucleon-nucleon interaction on a fixed LHC target is considered. It is shown that this process can be separated from the kinematically allowed production process using the existing detectors of the ALICE facility at a proton energy of 7 TeV with a fixed nuclear target. Assuming the scale dependence of the cross section, the data obtained can be used to estimate the subthreshold cross section for the production of superheavy particles with a mass of several tens of TeV in the LHC lead nucleus beam.

Theoretical predictions on cluster radioactivity of superheavy nuclei with Z=119,120

In this study,we investigate the cluster radioactivity(CR)of new superheavy elements with Z=119 and 120 based on two successful theoretical methods with modified parameters:the density-dependent cluster model(DDCM)and unified decay formula(UDF).First,we employ the DDCM and UDF to accurately reproduce the experimental half-lives of cluster emissions,which demonstrates the high reliability of our theoretical methods.Then,we systematically predict the probable cluster modes of ^(293-311)119 and ^(293-302)120 as well as their corresponding decay energies and half-lives.The half-lives of cluster decay derived from the DDCM are consistent with those from the UDF.Therefore,our results reveal that the cluster emission of ^(8)Be,emitted from the Z=119 and 120 isotopic chains,exhibits the minimum half-life for cluster emission,and hence,^(8)Be emission is considered the most probable cluster decay mode.Moreover,we explore the competition betweenαdecay and CR and find thatαdecay may be the dominant decay mode against CR.Furthermore,the good linear relationship between the decay energy and the number ofαparticles within the emitted cluster is extended to the range of superheavy nuclei(SHN).We anticipate that our theoretical predictions for CR will provide valuable references for the experimental synthesis of new SHN.

α-particle preformation factors in heavy and superheavy nuclei

In this study,α-particle preformation factors in heavy and superheavy nuclei from ^(220)Th to ^(294)Og are investigated.By combing experimental α decay energies and half-lives,the α-particle preformation factors P_(α) are extracted from the ratios between theoretical α decay half-lives calculated using the Two-Potential Approach (TPA)and experimental data.We find that the α-particle preformation factors exhibit a noticeable odd-even staggering behavior,and unpaired nucleons inhibit α-particle preformation.Moreover,we find that both the α decay energy and mass number of parent nucleus exhibit considerable regularity with the extracted experimental α-particle preformation factors.After considering the major physical factors,we propose a local phenomenological formula with only five valid parameters for α-particle preformation factors P_(α).This analytic expression has a clear physical meaning as well as good precision.As an application,this analytic formula is extended to estimate the α-particle preformation factors and further predict the α decay half-lives for unknown even-even nuclei with Z=118 and 120.

α-decay properties of superheavy nuclei with 117 ≤ Z ≤ 120 from the systematics of decay chains and isotopic chains

Recently, the synthesis of new elements above Z = 118 has been a hot topic in nuclear physics. Meanwhile, the α-decay chain is expected to be the unique tool to identify these heaviest nuclei. We have systematically calculated the α-decay energies and half-lives on the same footing for superheavy nuclei (SHN) within the cluster model along with a slightly modified Woods-Saxon (W.S.) potential as the nuclear potential. Based on the available experimental data, the key radius parameter (R) in the α-core potential is determined via the systematic trend from the α-decay and isotopic chains. The α-decay energy (Qα) values and half-lives are then obtained simultaneously for those unknown SHN in the range of 117 ≤ Z ≤ 120, during which the decay width is obtained using a new treatment for the asymptotic behavior of the α-core wave function. The theoretical values and experimental data are found to be in excellent agreement for the nuclei ^(293,294)117 and ^(294)118 regardless of the method used to determine the R parameter. Predicting the α-decay chains for new elements Z = 119 and Z = 120 can be useful in ongoing or forthcoming experiments.

Exploring the Feasibility of Producing Superheavy Nuclei in the Proton Evaporation Channel

The feasibility of producing superheavy nuclei in proton evaporation channels was systematically studied within the dinuclear system(DNS)model.Due to the Z=114 proton-shell,one can synthesize Fl isotopes in proton evaporation channels.We only considered the case of evaporating one proton first and then n neutrons in this work,other cases were ignored due to the small cross-section.The production cross sections of unknown isotopes ^(290,291)Fl in ^(38)S+^(255)Es reaction are the highest compared with ^(50)Ti+^(243)Np and ^(54)Cr+^(239)Pa reactions,and the maximum cross sections are 1.1 and 15.1 pb,respectively.^(42)S+^(254)Es is a promising candidate to approach the island of stability as the radioactive beam facilities are upgraded in the future,and the production cross sections of ^(291−294)Fl in that reaction are estimated to be 3.2,6.0,4.0,and 0.1 pb,respectively.

Evaporation residue cross sections of superheavy nuclei based on optimized nuclear data

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

An improved α-decay energy formula for heavy and superheavy nuclei

Based on the liquid-drop model and using the first derivative of the normalized Gaussian function to consider the shell correction,a simpleα-decay energy formula is proposed for heavy and superheavy nuclei.The values of corresponding adjustable parameters are obtained by fittingα-decay energies of 209 nuclei ranging from Z=90 to Z=118 with N≥140.The calculated results are in good agreement with the experimental data.The average and standard deviations between the experimental data and theoretical results are 0.141 and 0.190 Me V,respectively.For comparison,the reliable formulae proposed by Dong T K et al(2010,Phys.Rev.C 82,034320),Dong J M et al(2010,Phys.Rev.C 81,064309)and the WS3+nuclear mass model proposed by Wang N et al(2011,Phys.Rev.C 84,051303)are also used.The results indicate that our improved 7-parameter formula is superior to these empirical formulae and is largely consistent with the WS3+nuclear mass model.In addition,we extend this formula to predict theα-decay energies for nuclei with Z=117,118,119 and 120.The predicted results of these formulae are basically consistent.

Possibility of reaching the predicted center of the“island of stability”via the radioactive beam-induced fusion reactions

Based on the dinuclear system model,the synthesis of the predicted double-magic nuclei^(298)Fl and 304120 was investigated via neutron-rich radioactive beam-induced fusion reactions.The reaction^(58)Ca+^(244)Pu is predicted to be favorable for producing^(298)Fl with a maximal ER cross section of 0.301 pb.Investigations of the entrance channel effect reveal that the^(244)Pu target is more promising for synthesizing^(298)Fl than the neutron-rich targets^(248)Cm and^(249)Bk,because of the influence of the Coulomb barrier.For the synthesis of 304120,the maximal ER cross section of 0.046 fb emerges in the reaction^(58)V+^(249)Bk,indicating the need for further advancements in both experimental facilities and reaction mechanisms.

Multi-layer phenomena in petawatt laser-driven acceleration of heavy ions

Laser-accelerated high-flux-intensity heavy-ion beams are important for new types of accelerators.A particle-in-cell program(Smilei) is employed to simulate the entire process of Station of Extreme Light(SEL) 100 PW laser-accelerated heavy particles using different nanoscale short targets with a thickness of 100 nm Cr, Fe, Ag, Ta, Au, Pb, Th and U, as well as 200 nm thick Al and Ca. An obvious stratification is observed in the simulation. The layering phenomenon is a hybrid acceleration mechanism reflecting target normal sheath acceleration and radiation pressure acceleration, and this phenomenon is understood from the simulated energy spectrum,ionization and spatial electric field distribution. According to the stratification, it is suggested that high-quality heavy-ion beams could be expected for fusion reactions to synthesize superheavy nuclei. Two plasma clusters in the stratification are observed simultaneously, which suggest new techniques for plasma experiments as well as thinner metal targets in the precision machining process.