Production cross sections of the superheavy nucleus 117 based on the dinuclear system model

Within the framework of the dinuclear system model, the capture of two colliding nuclei, and the formation and de-excitation process of a compound nucleus are described by using an empirical coupled channel model, solving the master equation numerically and the statistical evaporation model, respectively. In the process of heavy-ion capture and fusion to synthesize superheavy nuclei, the barrier distribution function is introduced and averaging collision orientations are considered. Based on this model, the production cross sections of the cold fusion system ^76-82Se＋^209Bi and the hot fusion systems ^55Mn＋^238U, ^51V＋^244pu, ^59Co＋^232Th, ^48Ca＋^247-249Bk and ^45Sc＋^246-248Cm are calculated. The isotopic dependence of the largest production cross sections is analyzed briefly, and the optimal projectile-target combination and excitation energy of the 1n-4n evaporation channels are proposed. It is shown that the hot fusion systems ^48Ca＋^247-249Bk in the 3n evaporation channels and ^45Sc＋248Cm in the 2n-4n channels are optimal for synthesizing the superheavy element 117.

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.

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.

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.

原子核质量模型对预言新超重元素合成截面的影响

在双核系统模型(Dinuclear System Model,DNS)的框架下,深入讨论了不同核质量模型对计算超重核存活概率的影响,并进一步考察了它如何影响DNS预测超重新元素合成截面。不同核质量模型输出的核质量表具有较大差异,尤其对于未知核区。原子核质量作为DNS的核心输入量,它们在结合能、四极形变以及外推能力等方面的微小差异,都能对DNS的计算结果产生直接影响。此外发现,原子核质量是影响熔合概率和存活概率计算数值的关键因素。具体来说,不同核质量表提供的粒子分离能对超重核通过发射中子、质子、α粒子的衰变概率计算具有直接的影响。仔细分析超重核^(291)Mc的存活概率,我们发现随着蒸发中子数的增加,不同核质量表计算出的存活概率差异也会逐渐累积。值得注意的是,使用不同的核质量表进行超重核合成截面计算,其结果与实验数据相吻合,分布范围在一个数量级之内,这进一步验证了DNS预测的准确性。最后,讨论了五种核质量表对预测119、120号超重新元素合成截面的影响,误差范围在一个数量级之内。

Production of neutron-rich actinide isotopes in isobaric collisions via multinucleon transfer reactions

We systematically calculated the multinucleon transfer reactions of ^(208)Os,^(208)Pt,^(208)Hg,^(208)Pb,^(208)Po,^(208)Rn,^(208)Ra,and ^(132,136) Xe when bombarded on ^(232) Th and ^(248) Cm at Coulomb barrier energies within the dinuclear system model.These results are in good agreement with the available experimental data.The influence of Coulomb and shell effects on actinide production in these reactions has been rigorously studied.We calculated and analyzed the potential energy surface (PES) and total kinetic energy (TKE) mass distributions for the reactions involving ^(208)Hg,^(208)Pb,and ^(208) Po with ^(248) Cm and ^(232)Th.The PES and TKE spectra shed light on the fragment formation mechanisms in multinucleon transfer reactions,with clear indications of isospin and shell effects.The production cross sections for multinucleon transfer products show a strong dependence on isobar projectiles with a mass number A=208.Isobar projectiles with high N/Z ratios are advantageous for generating neutron-rich target-like fragments.Conversely,products induced by isobar projectiles with larger charge numbers tend to shift toward proton-rich regions.The intertwining of the Coulomb potential and shell effect is evident in the production cross sections of actinide isotopes.Drawing from reactions induced by radioactive projectiles,we anticipate the discovery of several new actinide isotopes near the nuclear drip lines,extending our reach into the superheavy nuclei domain.

Prediction of synthesis cross sections of new moscovium isotopes in fusion‑evaporation reactions

In the framework of the dinuclear system model,the synthesis mechanism of the superheavy nuclides with atomic numbers Z=112,114,115 in the reactions of projectiles 40,^(48)Ca bombarding on targets^(238)U,^(242)Pu,and^(243)Am within a wide interval of incident energy has been investigated systematically.Based on the available experimental excitation functions,the dependence of calculated synthesis cross-sections on collision orientations has been studied thoroughly.The total kinetic energy(TKE)of these collisions with fixed collision orientation shows orientation dependence,which can be used to predict the tendency of kinetic energy diffusion.The TKE is dependent on incident energies,as discussed in this paper.We applied the method based on the Coulomb barrier distribution function in our calculations.This allowed us to approximately consider all the collision orientations from tip-tip to side-side.The calculations of excitation functions of^(48)Ca+^(238)U,^(48)Ca+242Pu,and^(48)Ca+^(243)Am are in good agreement with the available experimental data.The isospin effect of projectiles on production cross-sections of moscovium isotopes and the influence of the entrance channel effect on the synthesis cross-sections of superheavy nuclei are also discussed in this paper.The synthesis cross-section of new moscovium isotopes 278−286 Mc was predicted to be as large as hundreds of pb in the fusion-evaporation reactions of^(35,37)Cl+^(248)Cf,^(38,40)Ar+^(247)Bk,^(39,41)K+247 Cm,^(40,42,44,46)Ca+^(243)Am,45 Sc+^(244)Pu,and^(46,48,50)Ti+237Np,51 V+^(238)U at some typical excitation energies.

Multinucleon transfer dynamics in nearly symmetric nuclear reactions

Within the framework of the dinuclear system model,the multinucleon transfer dynamics for nearly symmetric nuclear collisions has been investigated.The reaction mechanism in the systems of 198Pt+198Pt and 204Hg+198Pt was investigated at beam energies around the Coulomb barrier.It was found that the isotopic yields are enhanced with increased incident energy in the domain of proton-rich nuclides.However,the production on the neutron-rich side weakly depends on the energy.The angular distribution with the beam energy was also analyzed in the multinucleon transfer reactions.Projectile-like fragments were produced toward the forward emission with increasing incident energy.The target-like fragments manifested the opposite trend in the transfer reactions.

采用双核模型研究超重核合成机制

本文首先介绍了两种描述低能重离子核反应的理论,然后基于这些理论发展了一个描述超重核合成的理论模型,即双核模型(dinuclear system model)。不同于Adamian的处理,本文的模型采用数值求解主方程的方法来描述重离子的熔合过程,重点讨论了熔合过程中主方程的发展演化,选择一维至三维不同的宏观自由度说明重离子熔合机制,为今后进一步发展模型与预言新核素提供理论依据。

基于双核模型研究大质量转移反应中结团发射机制

本文借助双核模型,进行了对多核子转移反应中前平衡结团发射机制进行了系统研究。以反应系统^(12)C+^(209)Bi、^(40)Ca+^(208)Pb和^(48)Ca+^(238)U为例,重点分析了库仑位垒附近重离子碰撞产生前平衡轻粒子,如中子、质子、氘核、氚核、^(3)He、^(4)He、^(6)Li、^(7)Li、^(8)Be和^(9)Be时间演化、动能分布和角分布。研究结果表明:结团发射呈现出一定核结构效应,^(4)He发射概率与质子相当并远大于^(3)He。前平衡结团主要分布在“类弹”和“类靶”角度区域发射,其动能分布呈现出玻尔兹曼分布形式。考虑结团预形成因子后该方法可以拓展用于不稳定原子核引起的结团发射机制研究。

Possible Way to Synthesize Superheavy Element Z=117

Within the framework of the dinuclear system model, the production of superheavy element Z = 117 in possible projectile-target combinations is analysed systematically. The calculated results show that the production cross sections are strongly dependent on the reaction systems. Optimal combinations, corresponding excitation energies and evaporation channels are proposed, such as the isotopes^248.249 Bk in ^48 Ca induced reactions in 3n evaporation channels and the reactions ^45Sc＋246.248Cm in 3n and 4n channels, and the system ^51 V＋ 244pu in 3n channel.

The Harmonic Approximation in Heavy-Ion Reaction Study

The derivation of the harmonic approximation of the Hamiltonian of a model of coupled three-dimensional harmonic oscillator is presented. It is shown how the splitting of the total Hamiltonian into the intrinsic and collective Hamiltonians leads to the description of the mechanism for energy dissipation in physical systems.

Fusion Hindrance Factor of Heavy Nuclei Extracted from Experimental Data

The reactions of ^16O＋^204pb, ^82Se＋^138Ba and ^96Zr＋^124Sn lead to the same compound nucleus ^220Th. In terms of the assumption that the surviving probability is independent of entrance channel, we have extracted the fusion hindrance factor from the evaporation residue cross sections for the reactions of ^82Se＋^138 Ba and ^96Zr＋^124Sn and compared with the results calculated using a two-parameter Smoluchowski equation. The theoretical predictions are basically in agreement with the experimental data. It is found that the probability of forming a compact ^220Th is less than 10% for the reactions considered. For the systems more massive than ^220Th, fusion should be much more strongly suppressed due to the competition of quasifission with complete fusion. Understanding of this inhibition is essential to forming new superheavy nuclei.

Evaluation of pre-neutron-emission mass distributions of neutron-induced typical actinide fission using scission point model

The scission point model is improved by considering the excitation-dependent liquid drop model to calculate mass distributions for neutron-induced actinide nuclei fission.Excitation energy effects influence the deformations of light and heavy fragments.The improved scission point model shows a significant advance with regard to accuracy for calculating pre-neutron-emission mass distributions of neutron-induced typical actinide fission with incident-neutron-energies up to 99.5 MeV.The theoretical frame assures that the improved scission point model is suitable for evaluating the fission fragment mass distributions,which will provide guidance for studying fission physics and designing nuclear fission engineering and nuclear transmutation systems.

Angular distribution of products in multinucleon transfer reactions

A method based on the dinuclear system(DNS)is proposed to describe the angular distribution of products in multinucleon transfer(MNT)reactions.By considering fluctuation effects,the angular distributions of reactions involving^(136)Xe+^(208)Pb,^(136)Xe+^(209)Bi,^(86)Kr+^(166)Er,^(84)Kr+^(209)Bi,and^(84)Kr+^(208)Pb are examined,demonstrating good agreement with experimental data.Moreover,the double differential cross-sections(dσ^(2)/dl_(i)dΘand dσ^(2)/dZdΘ)of reactions^(136)Xe+^(208)Pb and^(136)Xe+^(209)Bi are analyzed to explore the mechanism of angular distribution in MNT reactions.Additionally,the optimal angles for detecting N=126 isotopes are determined via an analysis on the influence of proton and neutron numbers of the projectiles on the angular distribution of the N=126 isotopic line.The results of this study can provide valuable insights for experimental detection.

Possibility of synthesizing Z=119 superheavy nuclei with Z>20 projectiles

We employ the dinuclear system(DNS)model combined with a statistical model to calculate the evaporation residue cross sections of the reaction systems ^(48)Ca+^(243)Am,^(48)Ca+^(248)Cm,and ^(48)Ca+^(249)Bk.The theoretical results successfully reproduce the experimental trends in the 3n and 4n evaporation channels of these reaction systems.To synthesize the new element,we predict 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 note 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.

热熔合反应合成超重核产生截面的同位素依赖性

通过在形成超重核的重离子俘获和熔合过程中引入位垒分布函数的方法对双核模型做了进一步发展．超重核形成过程中的俘获、熔合和蒸发3个阶段分别采用了半经验的耦合道模型、数值求解主方程和统计蒸发模型的方法来描述．计算了近年来Dubna小组利用热熔合反应48Ca(243Am,3n-5n) 288-286115和48Ca(248Cm,3n-5n)293-291116合成超重新核素的蒸发余核激发函数．系统分析了48Ca轰击锕系元素U,Np,Pu,Am,Cm合成超重核Z=112-116产生截面的同位素依赖性．给出了合成超重新核素最佳的弹靶组合和入射能量,即有最大的超重核产生截面．计算说明,壳修正能和中子分离能是影响超重核生成截面产生同位素依赖性的主要因素．

Effects of entrance channel on fusion probability in hot fusion reactions

Within the framework of the dinuclear system （DNS） model, the fusion reactions leading to the compound nuclei 274Hs＊ and 2S6Cn＊ are investigated. The fusion probability as a function of DNS excitation energy is studied. The calculated results are in good agreement with the available experimental data. The obtained results show that the fusion probabilities are obviously enhanced for the reactions located at high place in potential energy surface, although these reactions may have small values of mass asymmetry. It is found that the enhancement is due to the large potential energy of the initial DNS.

Theoretical study on production cross sections of exotic actinide nuclei in multinucleon transfer reactions

Within the dinuclear system（DNS） model, the multinucleon transfer reactions 129,136Xe ＋248Cm,112Sn＋238U, and 144Xe ＋248Cm are investigated. The production cross sections of primary fragments are calculated with the DNS model. By using a statistical model, we investigate the influence of charged particle evaporation channels on production cross sections of exotic nuclei. It is found that for excited neutron-deficient nuclei the charged particle evaporation competes with neutron emission and plays an important role in the cooling process. The production cross sections of several exotic actinide nuclei are predicted in the reactions 112Sn ＋238U and 136,144Xe ＋248Cm.Considering the beam intensities, the collisions of 136,144Xe projectiles with a 248Cm target for producing neutron-rich nuclei with Z =92-96 are investigated.

Possibilities of synthesizing new proton-rich nuclei with 40≤Z≤60 using multinucleon transfer reactions

Multinucleon transfer reactions near the Coulomb barrier are investigated based on the improved dinuclear system(DNS)model,and the deexcitation process of primary fragments are described using the statistical model GEMINI++.The production cross sections of^(40,48)Ca+^(124)Sn and^(64)Ni+^(130)Te based on the DNS model+GEMINI++are calculated and compared with experimental data.The calculated results reproduce experimental data.The cross sections of fusion-evaporation,fragmentation,and multinucleon transfer reactions in the region are also provided in this paper.The results show that in the region,fusion-evaporation and fragmentation reactions have good results in the relatively proton-rich region,but in the extreme proton-deficient region,the MNT reaction is still promising for synthesizing proton-rich nuclei.