Nuclear Hexadecapole Deformation Effects on the Production of Super-Heavy Elements

We investigate the effects of the nuclear hexadecapole deformations on the interaction potentials between nuclei, the driving potentials and the fusion probabilities for some cold fusion reactions leading to super-heavy elements. It is found that nuclear hexadecapole deformations change significantly the structure of the driving potentials and the fusion probabilities for some reaction channels.     

Effective probabilities in a new approach to analyzing angular distributions in elastic heavy-ion scattering

A new approach proposed previously to analyze angular distributions in elastic heavy-ion scattering is generalized to cases where total partial probabilities (that is, those that are summed over all channels) of the enhancement of “fusion” (in general, complete and incomplete fusion, quasifission, and deep-inelastic collisions) are commensurate with the total partial probabilities of the suppression of “fusion.” This could be done with the aid of effective total partial probabilities, each of these being defined as a linear combination of actual total partial probabilities. It is shown that the probabilities introduced in this way have a specific physical meaning. Indeed, the effective total partial probabilities make it possible to calculate the cross section for “fusion” through the entrance channel and some reference total cross sections for peripheral processes, and a conclusion on whether fusion and peripheral reactions are enhanced or suppressed can be drawn from a comparison of the calculated or measured results for, respectively, the fusion cross section and the total cross section for peripheral reactions with the above two cross sections. It is also found that the enhancement of fusion is accompanied by the suppression of peripheral reactions, and vice versa.     

Entrance channel effects in fusion-evaporation processes

The effect of shape equilibration on particle emission in fusion reactions is thoroughly studied. Following a detailed evaluation of the various time scales a microscopic dynamical picture of the fusion path is coupled to a statistical decay probability at different time steps. It is shown that excitation energy and deformation of the compound system are influencing the emission pattern of charged particles and Giant Dipole photons. A quantitative analysis is performed for a ¹⁶⁴Yb compound system formed via O + Sm (mass asymmetric) and Ni + Mo (mass symmetric) channels at various excitation energies. In the mass-symmetric case interesting effects are revealed on spectra and angular distributions of emitted particles, particularly for α's, protons and Giant Dipole photons. Experiments are suggested to directly measure these “pre-equilibrium” contributions leading to new information on very exotic hyperdeformed nuclear systems.     

How well do we understand the synthesis of heavy elements by heavy-ion induced fusion?

Experimental cross sections to synthesize heavy ion induced fusion reactions are confronted with calculations using the conventional picture of complete fusion after passing the barrier plus statistical deexcitation after complete equilibration. The sensitivity of the calculations to some of the parameters is demonstrated. Despite this sensitivity, a single parameter set is found that reproduces well the large body of data from experiments using actinide targets. By comparison, for the more symmetric entrance channels using targets around²⁰⁸Pb, we find a fusion hindrance that increases steeply with increasing compound nuclear charge. Predictions for a few reactions of future interest for the synthesis of heavy elements are also presented.     

Deuteron disintegration, thermonuclear and nuclear fission reactions induced by γ-quanta in D-saturated palladium and dense deuterium gas with synthesis of new structures

The results obtained by investigating the chemical composition and structure of Pd sample sur-faces, chamber components, and a new synthesized object (NSO) are presented. The NSO is produced in the chamber with a high-pressure (about 3 kbar) deuterium gas under irradiation by γ-quanta with an energy of 8.8 MeV. The measured concentrations of chemical elements arisen from nuclear reactions initiated by γ-quanta have made it possible to develop the phenomenological approach to describing the process whereby deuterium atoms are heated by the protons and neutrons of a deuteron photofission reaction, hot D-D fusion, Oppenheimer reactions, and palladium nuclear fission. The coefficient of the process efficiency greatly exceeds unity. A new type of reactors (deuterated nuclear fission reactor) is proposed.     

Dynamical effects of spin-dependent interactions in low- and intermediate-energy heavy-ion reactions

It is well known that noncentral nuclear forces, such as the spin–orbital coupling and the tensor force, play important roles in understanding many interesting features of nuclear structures. However, their dynamical effects in nuclear reactions are poorly known because only the spin-averaged observables are normally studied both experimentally and theoretically. Realizing that spin-sensitive observables in nuclear reactions may convey useful information about the in-medium properties of noncentral nuclear interactions, besides earlier studies using the time-dependent Hartree–Fock approach to understand the effects of spin–orbital coupling on the threshold energy and spin polarization in fusion reactions, some efforts have been made recently to explore the dynamical effects of noncentral nuclear forces in intermediate-energy heavy-ion collisions using transport models. The focus of these studies has been on investigating signatures of the density and isospin dependence of the form factor in the spin-dependent single-nucleon potential. Interestingly, some useful probes were identified in the model studies but so far there are still no data to compare with. In this brief review, we summarize the main physics motivations as well as the recent progress in understanding the spin dynamics and identifying spin-sensitive observables in heavy-ion reactions at intermediate energies. We hope the interesting, important, and new physics potentials identified in the spin dynamics of heavy-ion collisions will stimulate more experimental work in this direction.     

A new scenario for the application of very intense lasers to nuclear fusion

The ponderomotive motion of a charged particle inside a Terawatt-Petawatt laser pulse is studied. Based on a very simple classical model to account for the Coulomb repulsion, the possibility of nuclear collisions in the keV-MeV range is shown. Also, a simple analytical expression for the minimum internuclear distance is given. Since this range of energies is significant to trigger nuclear fusion reactions, this may result in an alternative approach to controlled fusion based on a non-thermalized plasma. The proposed system works for the deuterontriton fusion reaction, but is more appropriate for other reactions like the proton-⁷Li reaction, and also like the ecologically clean, boron-¹¹B reaction.     

Generation of neutrons in giant upward atmospheric discharges

It has been shown that the efficiency of the reactions of the fusion of deuterons in the atmosphere is very low; therefore, nuclear fusion cannot be responsible for the generation of neutrons by lightning. The generation of neutrons in thunderstorm fields is attributed to photonuclear reactions in giant upward atmospheric discharges over thunderclouds.     

Heavy ion induced charge exchange reactions: A preliminary study within the Constrained Molecular Dynamics model

We present a preliminary study of charge exchange heavy ion induced reactions based on the constrained molecular dynamics(CoMD) model.The purpose is to test the capability of the model in predicting the occurrence of single charge exchange(SCE) and double charge exchange(DCE) exit channels for three different entrance channels at the same laboratory incident energy.The nuclear reaction dynamics and nuclear interaction within the CoMD approach are the only ingredients that have given,at this stage,promising results for SCE and DCE cross section calculations.The obtained results suggest an upgrade and possible future employment of the model for studies relating to the production of exotic nuclei through charge exchange reactions or DCE reactions and their connection with neutrinoless double beta decay.     

Synthesis of superheavy elements and the process of complete fusion of massive nuclei

The development of various approaches to describing the complete fusion of nuclei and their connections with experimental studies is discussed. A brief account of the dinuclear-system concept (DNSC), the approach proposed at Dubna, is given. The DNSC revealed two important features of the complete fusion of massive nuclei: the existence of the inner fusion barrier B _fus ^* and the competition between complete fusion and quasifission channels in a dinuclear system formed at the capture stage. The DNSC was applied to the analysis of reactions used to synthesize superheavy elements (SHE). The DNSC provided a basis for the models of competition between complete-fusion and quasifission channels. Using these models, one can describe the cross section for SHE production in cold-and warm-fusion reactions.     

反质子引起的核反应中碎裂机制和粒子产生（英文）

基于兰州量子分子动力学（LQMD） 模型,系统研究了低能反质子引起的核反应中原子核碎裂机制和粒子产生。在LQMD输运模型中,考虑了反重子-重子、重子-重子和介子-重子碰撞可能产生的弹性散射、湮灭反应、电荷交换和非弹性散射。发展了并合模型,用于相空间构造初级碎片产生。处于激发态的碎片退激是基于统计模型描述。研究结果说明超子主要是由于奇异性交换产生;重碎片裂变会导致中等质量区域碎片产额增加;反质子引起的核反应有利于产生s=-2 和s=1 奇特超核,并给出了产生截面。Within the framework of the Lanzhou quantum molecular dynamics (LQMD) transport model, the nuclear fragmentation and particle production induced by low-energy antiprotons have been investigated thoroughly. Production of strange particles in the antiproton induced nuclear reactions is modeled within the LQMD model, in which all possible reaction channels such as elastic scattering, annihilation, charge exchange and inelastic scattering in antibaryon-baryon, baryon-baryon and mesonbaryon collisions have been included. A coalescence approach is developed for constructing the primary fragments in phase space. The secondary decay process of the fragments is described by the well-known statistical code. It is found that the strangeness exchange reactions dominate the hyperon production. A bump structure in the domain of intermediate mass for heavy targets appears owing to the contribution of fission fragments. It has advantage to produce heavier hyperfragments and hypernuclides with strangeness s = -2 (double-Λ fragments) and s = 1 (Λ-fragments) in antiproton induced reactions. The production cross sections are evaluated.     

Correlations between nucleon transfer and fusion at near-barrier energies for the systems32S +100,101Ru and33S +90,91,92Zr

Transfer reactions at two near-barrier energies for the systems³²S +^100,101Ru have been studied. Differential cross sections have been extracted for a large variety of channels, with a set-up yielding good mass, nuclear charge and energy resolutions. A steeper decrease of the measured angular distributions at backward angles with respect to the prediction of a semiclassical theory is interpreted as a loss of transfer flux feeding more complex channels and/or fusion. Coupled channels calculations, which use the transfer form factors derived from the experiment, reproduce the fusion cross sections at sub-barrier energies. Multi-nucleon transfer seems to play an essential role for the fusion process, as evidenced by the found strong correlations. A systematic comparison is made with the systems³³S +^90,91,92Zr, which have been the object of a previous experimental study with the same set-up.     

The stability of cones and pyramids on sputtered surfaces of copper

A new modification of an earlier published model for the calculation of energy spectra of primary knocked atoms formed in the material under neutron, proton or other particle irradiation is being considered in the present paper. The new approach takes into account the angular momenta of interacting particles within the limits of the compound nucleus model. It is found that the model allows to carry out more accurate estimation of the quantities of nuclear reaction products. It also modifies the shape of the PKA energy spectrum. Control calculations for the nuclear reactions caused in proton irradiated copper have been made. The results of these calculations are in good agreement with the excitation functions for the nuclear reactions.     

The Ab Initio No-core Shell Model

This contribution reviews a number of applications of the ab initio no-core shell model (NCSM) within nuclear physics and beyond. We will highlight a nuclear-structure study of the A = 12 isobar using a chiral NN + 3NF interaction. In the spirit of this workshop we will also mention the new development of the NCSM formalism to describe open channels and to approach the problem of nuclear reactions. Finally, we will illustrate the universality of the many-body problem by presenting the recent adaptation of the NCSM effective-interaction approach to study the many-boson problem in an external trapping potential with short-range interactions.     

基于双核模型的粒子交换势能面与熔合几率的研究(英文)

研究了基于双核模型的粒子交换势能面.原子核的形变效应对于势能面的形状有较大的影响.在反应过程中,作为反应时间函数的动态形变的变化是显著的.通过求解主方程,对一些基于冷熔合机制的反应道的全熔合几率也进行了讨论. The Potential Energy Surface (PES) for particle exchange in Di nuclear system is studied in detail. It is found that the nuclear deformation effect can change the shape of PES significantly. The dynamical deformation as a function of the reaction time in the reaction process is investigated in a simple model and we found that its variation with time is dramatic. The fusion probabilities P-CN of some reaction channels based on the mechanism of cold fusion are also calculated.     

Recent Experiments Involving Few-Nucleon Systems

Recent experimental results are presented for reactions involving A = 3 to A = 6 nuclear systems. The emphasis is on unique data obtained at new experimental facilities. It is shown that the inertial confinement fusion facilities OMEGA and NIF provide a largely unexpected opportunity for experimental few-body physics to both obtain data of unprecedented quality and extend previous measurements to energies not accessible in the past. Whenever possible, data are compared to state-of-the-art theoretical calculations.     

Radiation effect of neutrons produced by D–D side reactions on a D–3He fusion reactor

One of the most important characteristics in D–³He fusion reactors is neutron production via D–D side reactions. The neutrons can activate structural material, degrading them and ultimately converting them into high-level radioactive waste, while it is really costly and difficult to remove them. The neutrons from a fusion reactor could also be used to make weapons-grade nuclear material, rendering such types of fusion reactors a serious proliferation hazard. A related problem is the presence of radioactive elements such as tritium in D–³He plasma, either as fuel for or as products of the nuclear reactions; substantial quantities of radioactive elements would not only pose a general health risk, but tritium in particular would also be another proliferation hazard. The problems of neutron radiation and radioactive element production are especially interconnected because both would result from the D–D side reaction. Therefore, the presentation approach for reducing neutrons via D–D nuclear side reactions in a D–³He fusion reactor is very important. For doing this research, energy losses and neutron power fraction in D–³He fusion reactors are investigated. Calculations show neutrons produced by the D–D nuclear side reaction could be reduced by changing to a more ³He-rich fuel mixture, but then the bremsstrahlung power loss fraction would increase in the D–³He fusion reactor.     

Effect of positive Q-value neutron transfers on sub-barrier fusion reactions

The role of positive Q-value neutron transfers in sub-barrier fusion reactions has been studied with a modified quantum coupled channels model with all order couplings(CCFULL model). Neutron rearrangement related only to the dynamical matching condition with no free parameters is implemented in the model, which provides a way to understand especially the Q-value dependence of sub-barrier fusion reactions. The fusion cross sections of the collision systems ~(40)Ca+~(94,96)Zr have been calculated and analyzed. The general trend of experimental data can be reproduced well with additional channels for neutron rearrangement. We find that enhancement of sub-barrier fusion cross sections is closely related to the Q-value of the transferred neutrons, in particular for channels with sequential even number transferred neutrons.