基于双核模型对Z = 116~ 121 超重核产生截面的研究(英文)

在双核模型的理论框架下系统研究了超重元素Z = 116 ~121 的蒸发剩余截面,计算过程中核子扩散由主方程描述,同时考虑了全熔合与准裂变的竞争。计算基本再现了利用热熔合反应48Ca+245Cm,48Ca+249Cf 和48Ca+249Bk 产生116~118 号同位素的合成截面。同样,分别以249Bk,249Cf 和243Am 为靶,以48Ca,50Ti 和58Fe 为炮弹,计算了Z = 119~ 121 号同位素的生成截面。结果表明,这些超重核的生成截面随着质子数的增大进一步变小。例如,利用58Fe+243Am 反应合成121 号同位素的最大蒸发剩余截面仅在fb 量级。基于对选择的几个反应系统的系统分析,发现双核系统在熔合蒸发过程中偶Z 奇N 和奇Z 偶N 复合核分别有强的3n 和4n 蒸发道。The production cross sections of superheavy elements with Z = 116~121 have been investigated systematically within the dinuclear system (DNS) concept, where the master equation is solved numerically to obtain the fusion probability. The competition between complete fusion and quasifission, which can strongly affect the cross section of the compound nucleus formation, is taken into account. The evaporation residue cross sections ER calculated for the hot fusion actinide-based reactions (48Ca+245Cm, 48Ca+249Cf and 48Ca+249Bk) are basically in agreement with the known experimental data within one order of magnitude. Similar calculations for the synthesis of superheavy elements up to Z = 121 are performed using the available 249Bk, 249Cf and 243Am as targets and 48Ca, 50Ti and 58Fe as projectiles. Their production cross sections are relatively small,especially for the 58Fe+243Am→301121 reaction. A systematic analysis indicates that the 3n and 4n channelsare respectively the most favorable fusion-evaporation channels in the synthesis of even- and odd-Z superheavy elements.     

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.     

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。     

基于双核模型对超重元素合成机制的研究

在双核模型基础上，考虑了熔合与准裂变的竞争，通过数值法求解主方程，计算了⁵⁰Ti，⁵⁸Fe+²⁰⁸Pb，²⁰⁹Bi这4个反应系统通过冷熔合反应合成超重元素的激发函数，得到了与实验比较符合的结果.计算了不同入射能量时各角动量分波对熔合概率和超重核存活概率的影响以及对蒸发剩余截面的贡献.这些结果对进一步理解超重核的合成机制有重要意义. 关键词： 超重元素 双核模型 熔合反应 蒸发剩余截面     

不同理论模型预言合成超重核Z=119~122研究进展

通过双核系统模型与其他模型对$Z\leqslant$118元素的计算结果与实验数据的比较,证明了不同模型预测超重核的产生截面是可靠的。对比分析了不同模型对Z=119和Z=120超重核的预言结果,我们认为合成超重核Z=119和Z=120的最佳弹靶组合分别为反应$^{48}{\rm{Ca}} + ^{{\rm{252}}}{\rm{Es}}$和$^{40}{\rm{Ca}} + ^{{\rm{257}}}{\rm{Fm}}$,并且Z=119新核素很有可能会先于Z=120新核素在实验上被合成。由于实验上Z>100锕系靶的限制,人们正尝试寻找比48Ca更重的弹核来合成超重核Z=121和Z=122,超重核Z=121可以通过反应V+Cf来合成,而超重核Z=122的产生截面已经非常小,要求将来在实验上提高探测及鉴别技术。希望本文的讨论可以在将来为实验及理论核物理工作者们提供一些参考。     

生成超重核的熔合反应中的动力学形变效应

利用包含动力学势能面的双核模型对超重核的生成机制中的一些问题进行了研究。对双核系统的粒子交换势能面进行的计算结果表明,反应过程中原子核动力学形变对于粒子交换势能面的结构有显著的影响。进一步计算了生成超重核的熔合几率,结果显示,原子核的动力学形变导致内熔合位垒升高,进而明显降低了生成超重核的熔合几率。Some aspects in the fusion mechanism for the production of superheavy nuclei are investigated with the dinuclear system model with dynamical potential energy surface. The calculation results about the potential energy surface indicate that the inclusion of nuclear dynamical deformation affects the structure of potential energy surface significantly.The investigation on the fusion probability to synthesize superheavy nuclei indicates that the fusion probability decreases significantly due to the increase of the inner fusion barrier for the inclusion of the nuclear dynamical deformation.     

超重核熔合中的靶核形变效应

利用额外推力模型研究了⁴⁸Ca+²³⁸U俘获和熔合过程中的靶核形变效应.计算表明,在近垒和垒下能区,靶核形变使俘获截面和熔合截面增强,形成的复合核自旋分布展宽.     

超重核合成中的靶核形变效应

利用额外推力模型研究了48Ca+238U超重核合成过程中的靶核形变效应.计算表明,在近垒和垒下能区,靶核形变使超重核合成截面明显增强.对于48Ca+238U反应,由于靶核形变蒸发残余截面增大了几倍.同时与球形靶核相比,形变靶核时蒸发残余激发函数的峰位移向较低能量.Effects of target deformation on the synthesis of superheavy nucleus~(283)112 are investigated in the framework of extra-push model. Our results show that the cross sections of the 3n evaporation residue in the~(48)Ca+~(238)U reaction for the case of β_2=0.275 are several times larger than those of β_2=0. Meanwhile, the peak position of ER excitation function in the case of deformed target is shifted to the lower energy as compared to the one of spherical target.     

超重核合成理论模型简介

介绍并讨论了研究超重核合成的主要理论模型以及近年来在研究重核熔合机制和超重核合成理论模型方面的进展。 The theoretical models for investigating the fusion mechanism of heavy nucleus collisions and calculating the formation cross sections of superheavy nuclei have been introduced. The recent development and the present status for understanding the fusion mechanism of heavy nucleus collisions have been discussed.     

重离子熔合反应形成超重核的截面研究

在双核系统框架下,通过数值法解主方程计算了双核间的核子跃迁全熔合几率.两碰撞核内部激发能由相对运动能损提供,因此能够将核子转移过程与相对运动耦合起来.对一些以Pb为靶的形成超重核的冷熔合反应,计算了最佳激发能、形成双核系统的俘获截面、复合核形成几率及存活几率等,所得到的形成超重核蒸发剩余截面与已知实验值符合较好. In the concept of Dinuclear system (DNS) the complete fusion probability of two touch nuclei via nucleon transfer is described by numerically solving the Master equation. The excitation energy of two colliding nuclei is supplied by the energy dissipation of their relative motion, thus the nucleon transfer process and the relative motion are coupled. For Pb based cold fusion reactions to form super heavy nuclei, the optimal excitation energy, the capture cross section to form a DNS ...     

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 func-tion 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,59 Co+232 Th,48 Ca+247-249 Bk and 45 Sc+246-248 Cm 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 ln-4n evaporation channels are proposed.It is shown that the hot fusion systems 48Ca+247 249Bk in the3n evaporation channels and 45Sc+248Cm in the 2n-4n channels are optimal for synthesizing the superheavy element 117.     

Shell effect and capture cross sections in the synthesis of superheavy nuclei

The shell effect is included in the improved isospin dependent quantum molecular dynamics model in which the shell correction energy of the system is calculated by using the deformed two-center shell model.A switch function is introduced to connect the shell correction energy of the projectile and the target with that of the compound nucleus during the dynamical fusion process.It is found that the calculated capture cross sections reproduce the experimental data quantitatively at the energy near the Coulomb...     

Possibilities of producing superheavy nuclei in multinucleon transfer reactions based on radioactive targets

The multinucleon transfer(MNT) process has been proposed as a promising approach to produce neutronrich superheavy nuclei(SHN).MNT reactions based on the radioactive targets ~(249)Cf,~(254)Es,and ~(257)Fm are investigated within the framework of the improved version of a dinuclear system(DNS-sysu) model.The MNT reaction~(238)U+~(238)U was studied extensively as a promising candidate for producing SHN.However,based on the calculated cross-sections,it was found that there is little possibility to produce SHN in the reaction ~(238)U+~(238)U.In turn,the production of SHN in reactions with radioactive targets is likely.     

Production mechanism of superheavy nuclei in massive fusion reactions

Within the concept of the dinuclear system (DNS), a dynamical model is proposed for describing the formation of superheavy nuclei in complete fusion reactions by incorporating the coupling of the relative motion to the nucleon transfer process. The capture of two heavy colliding nuclei, the formation of the compound nucleus and the de-excitation process are calculated by using an empirical coupled channel model, solving a set of microscopically derived master equations numerically and applying statistical theory, respectively. Fusion-fission reactions and evaporation residue excitation functions of synthesizing superheavy nuclei (SHN) are investigated systematically and compared them with available experimental data. The possible factors that affecting the production cross sections of SHN are discussed in this workshop.     

Production mechanism of superheavy nuclei in massive fusion reactions

Within the concept of the dinuclear system (DNS), a dynamical model is proposed for describing the formation of superheavy nuclei in complete fusion reactions by incorporating the coupling of the relative motion to the nucleon transfer process. The capture of two heavy colliding nuclei, the formation of the compound nucleus and the de-excitation process are calculated by using an empirical coupled channel model, solving a set of microscopically derived master equations numerically and applying statistical theory, respectively. Fusion-fission reactions and evaporation residue excitation functions of synthesizing superheavy nuclei (SHN) are investigated systematically and compared them with available experimental data. The possible factors that affecting the production cross sections of SHN are discussed in this workshop.     

超重核合成的同位素依赖探讨

利用二参量Smoluchowski方程计算了54Fe+204Pb,56Fe+206Pb,58Fe+208Pb冷熔合和32,34,36S+238U热熔合的复合核形成截面和蒸发残余截面, 结果清楚地显示出超重核合成截面随同位素的变化。 由于较低的入射道库仑位垒、 较低的不对称裂变谷中的条件鞍点和较小的中子分离能, 一般地说, 丰中子同位素的超重核形成截面明显增强。 The cross sections of the compound nucleus formation and e vaporation residue for the 54Fe+204Pb, 56Fe+206Pb, 58Fe+208Pb cold fusion and 32,34, 36S+238U hot fusion have been calculated by using a two parameter Smoluchowski equation. Our results clearly show the isotope dependence of superheavy nucleus production. The formation cross sections of the neutron rich isotope are, generally speaking, obviously enhanced due to the lower Coloumb barrier , lower height of the conditional saddle point, and smaller neutron separation energy.     

Optimal reactions for the synthesis of superheavy nucleus 270Hs

The superheavy nucleus 270 Hs iS expected to be a "double-magic" deformed nucleus.We have calculated its cross sections of evaporation residue for the reactions 248Cm(26Mg,4n)270Hs,244pu(30Si,4n)270Hs,238U(36S,4n)270Hs and 226Ra(48Ca,4n)270Hs using a two-parameter Smoluchowski equation.It is found from our results that 226Ra(48Ca,4n)270Hs and 238U(36S,4n)270Hs are two optimal reactions for the synthesis of the superheavy nucleus 270Hs due to their large negative Q-values.     

He-HF体系势能模型对散射截面影响的理论研究

用BFW势函数拟合在CCSD(T)/aug-cc-pVQZ理论水平下计算的He-HF相互作用能，获得了He原子与HF分子相互作用的各向异性势，并与其他势模型进行比较，验证了拟合势的可靠性；然后采用量子密耦(Close-Coupling)方法分别计算了He-HF碰撞体系在五种不同势能模型下的微分散射截面、分波散射截面和总截面，并对计算结果进行了详细的比较和分析.研究表明：势能球平均零点能位置、势阱深度、排斥势的强度以及势能在势阱附近的方向性都对散射截面有较大影响. 关键词： 势能模型 密耦方法 散射截面