Geometrical aspects of isoscaling

The property of isoscaling in nuclear fragmentation is studied using a simple bond percolation model with “isospin” added as an extra degree of freedom. It is shown, first, that with the assumption of fair sampling and with homogeneous probabilities it is possible to solve the problem analytically. Second, numerical percolations of hundreds of thousands of grids of different sizes and with different N to Z ratios confirm this prediction with remarkable agreement. It is thus concluded that isoscaling emerges even in the simple case of a classical non-interacting system such as two-species percolation under the assumption of fair sampling; if put in the nomenclature of the minimum information theory, isoscaling in percolation appears to require nothing more than the existence of equiprobable configurations in maximum entropy states.     

Reaction dynamics with exotic nuclei

We review the new possibilities offered by the reaction dynamics of asymmetric heavy-ion collisions, using stable and unstable beams. We show that it represents a rather unique tool to probe regions of highly asymmetric nuclear matter (ANM) in compressed as well as dilute phases, and to test the in-medium isovector interaction for high-momentum nucleons. The focus is on a detailed study of the symmetry term of the nuclear equation of state (EOS) in regions far away from saturation conditions but always under laboratory controlled conditions.

Thermodynamic properties of ANM are surveyed starting from non-relativistic and relativistic effective interactions. In the relativistic case, the role of the isovector–scalar δ-meson is stressed. The qualitative new features of the liquid–gas phase transition, “diffusive” instability and isospin distillation, are discussed. The results of ab initio simulations of n-rich, n-poor, heavy-ion collisions, using stochastic isospin-dependent transport equations, are analyzed as a function of beam energy and centrality. The isospin dynamics plays an important role in all steps of the reaction, from prompt nucleon emissions to the final fragments. The isospin diffusion is also of large interest, due to the interplay of asymmetry and density gradients. In relativistic collisions, the possibility of a direct study of the covariant structure of the effective nucleon interaction is shown. Results are discussed for particle production, collective flows and isotransparency.

Perspectives of further developments of the field, in theory as well as in experiment, are presented.     

Isospin effects of projectile fragmentation in a Boltzmann-Langevin approach

The iso spin effects of projectile fragmentation at intermediate energies are investigated using an iso spindependent Boltzmann-Langevin model.The collisions of mass-symmetric reactions including ~(58)Fe,~(58)Ni+~(58)Fe,and~(58)Ni at intermediate energies,in the 30 to 100 MeV/A range,are studied for different symmetry energies.Yield ratios of the isotopic,isobaric,and isotonic pairs of fragments from the intermediate-mass region using three symmetry energies are extracted as functions of the N/Z ratio of the composite systems in the entrance channel and the incident energies.It is found that the yield ratios are sensitive to symmetry energies,especially for neutron-rich systems,and the calculations using soft symmetry energy are closer to the experimental data.The iso spin effect is stronger for the soft symmetry energy,owing to the competition of the repulsive Coulomb force and the symmetry energy attractive force on the proton.For the first time,the splits are presented,revealing a transition from the iso spin equilibrium at lower energies to translucency at intermediate energies.The results show a degree of transparency in that intermediate mass fragments undergo a transition from dependence on the composite systems in the entrance channel to reliance on the projectile and target nuclei.     

Target effect on fragmentation reaction at E = 290A MeV

The longitudinal and transverse momentum (P_L and PYen_T) distributions of projectile-like fragments, which were produced with an Ar beam and various targets (C, Al, Nb, Tb, Au), were measured at E=290A MeV. No significant target effects are found in P _L distribution. The width of P_T distribution increases with target mass. It is plausible that this result is explained by the deflection of orbit arising from Coulomb repulsion. The nuclear structural effects are observed in isotopic and isotonic distributions of production cross-sections of fragments, which are derived from observed momentum distributions.     

Neck dynamics

Intermediate-energy heavy-ion reactions produce a mid-rapidity region or neck, mostly in the semiperipheral collisions. Brief theory and experiment surveys are presented. General properties of the mid-rapidity zone are reviewed and discussed in the framework of reaction dynamics. Hierarchy effect, neutron enrichment, isospin diffusion are all new neck phenomena which are surveyed. The main neck observables are also examined, mainly in the context of the symmetry term of the nuclear equation of state.     

强激光间接驱动材料动态破碎过程的实验技术研究

强激光驱动加载已成为冲击波作用下材料动态破碎过程研究的一种有效手段.采用间接驱动方式,设计合适的腔型进行物理实验研究,可实现更大且更均匀的冲击加载一维区.采用数值模拟和物理实验方法,研究强激光间接驱动材料动态破碎过程的实验技术.首先,利用IRAD程序设计适用于开展动态破碎过程研究的半柱腔,其直径为2 mm、腔长为2 mm;进而通过物理实验获得此腔型下多个激光能量点、脉宽2 ns和3 ns条件下辐射峰值温度和波形;最后,利用流体模拟方法给出多种辐射波形下的冲击加载波形.利用高能X射线成像和光子多普勒干涉仪诊断给出间接驱动加载下层裂过程的物理图像和速度历史.经分析发现,间接驱动的加载一维区达到2 mm,平面性优于5%,能有效地开展相关物理实验研究.研究结果为新型柱腔设计、冲击加载技术及动态破碎过程研究提供了重要的研究基础.     

高能铁离子在水介质中核反应过程所导致的能量沉积

在银河宇宙射线中,400MeV/nucleon的铁离子通量相对来讲是较高的,400MeV/nucleon的铁离子对空间辐射引起的损伤和辐射剂量有重要的贡献.本文以Geant4为基础,对400MeV/nucleon Fe离子与物质相互作用后通过核反应过程产生的次级碎片进行模拟分析.对铁离子在水中产生的能量沉积和铁离子与水介质发生核反应后产生的次级碎片的能量沉积进行了模拟研究,得到了通过核反应过程产生次级粒子所导致的剂量贡献. 关键词： 能量沉积 剂量 碎片     

Study of the reaction step preceding sequential fission in the nuclear interaction (16.7 MeV/u) U+Au

The kinematical analysis of nuclear reactions between (16.7 MeV/u) ²³⁸U and ^nat.Au ions has been performed by using mica solid-state track detectors (SSNTD). The reaction products emanating from each isolated collision vertex were registered in the forward hemisphere with almost 2π angular coverage. It has been demonstrated previously that these tracks represent the second stage of a sequential fission process. In this paper the results of analysis pertaining to the first reaction step have been presented. Using a computer code based on the procedure of internal calibration it was possible to derive quantities like mass transfer, total kinetic energy loss, and scattering angles. It is shown that the mass flow and kinetic energy distribution between reacting partners interacting at different impact parameters during the first phase of the interaction decides the multiplicity of the final reaction products.     

Laser fragmentation in liquid synthesis of novel palladium-sulfur compound nanoparticles as efficient electrocatalysts for hydrogen evolution reaction

One promising way to tune the physicochemical properties of materials and optimize their performance in various potential applications is to engineer material structures at the atomic level. As is well known, the performance of Pd-based catalysts has long been constrained by surface contamination and their single structure. Here, we employed an unadulterated top-down synthesis method, known as laser fragmentation in liquid (LFL), to modify pristine PdPS crystals and obtained a kind of metastable palladium-sulfur compound nanoparticles (LFL-PdS NPs) as a highly efficient electrocatalyst for hydrogen evolution reaction (HER). Laser fragmentation of the layered PdPS crystal led to a structural reorganization at the atomic level and resulted in the formation of uniform metastable LFL-PdS NPs. Noteworthy, the LFL-PdS NPs show excellent electrocatalytic HER performance and stability in acidic media, with an overpotential of -66 mV at 10 mA· cm^-2, the Tafel slope of 42 mV· dec^-1. The combined catalytic performances of our LFL-PdS NPs are comparable to the Pt/C catalyst for HER. This work provides a top-down synthesis strategy as a promising approach to design highly active metastable metal composite electrocatalysts for sustainable energy applications.     

裂变路径对断点前粒子发射的影响

用扩散模型研究了裂变系统从鞍点到断点的时间演化, 以及在此间的粒子发射与鞍点前粒子发射的比随着裂变系统质量的变化. 解释了实验上发现的断点前粒子多重性随裂变碎片质量不对称性的变化趋势. 结果表明上述两种变化趋势都可以归因于裂变演化路程长短的影响.     

Calculation of prompt fission neutron spectrum for 233U（n,f）reaction by the semi-empirical method~

The prompt fission neutron spectra for the neutron-induced fission of ²³³U for low energy neutrons (below 6 MeV) are calculated using nuclear evaporation theory with a semi-empirical method, in which the partition of the total excitation energy between the fission fragments for the n_th+²³³U fission reactions is determined by the available experimental and evaluation data. The calculated prompt fission neutron spectra agree well with the experimental data. The proportions of high-energy neutrons of prompt fission neutron spectrum versus incident neutron energies are investigated with the theoretical spectra, and the results are consistent with the systematics. The semi-empirical method could be a useful tool for the prompt evaluation of fission neutron spectra.     

Anionic redox reaction mechanism in Na-ion batteries

Na-ion batteries (NIBs), as one of the next-generation rechargeable battery systems, hold great potential in large-scale energy storage applications owing to the abundance and costeffectiveness of sodium resources. Despite the extensive exploration of electrode materials, the relatively low attainable capacity of NIBs hinders their practical application. In recent years, the anionic redox reaction (ARR) in NIBs has been emerging as a new paradigm to deliver extra capacity and thus offers an opportunity to break through the intrinsic energy density limit. In this review, the fundamental investigation of the ARR mechanism and the latest exploration of cathode materials are summarized, in order to highlight the significance of reversible anionic redox and suggest prospective developing directions.     

Effects of Isospin on Pre-scission Particle Multiplicity of Heavy Systems and Its Excitation Energy Dependence

Isospin effects on particle emission of fissioning isobaric sources ²⁰²Fr, ²⁰²Po, ²⁰²Tl and isotopic sources ^189,202,212Po, and its dependence on the excitation energy are studied via Smoluchowski equations. It is shown that with increasing the isospin of fissioning systems, charged-particle emission is not sensitive to the strength of nuclear dissipation. In addition, we have found that increasing the excitation energy not only increases the influence of nuclear dissipation on particle emission but also greatly enhances the sensitivity of the emission of pre-scission neutrons or charged particles to the isospin of the system. Therefore, in order to extract dissipation strength more accurately by taking light particle multiplicities it is important to choose both a highly excited compound nucleus and a proper kind of particles for systems with different isospins.     

Double hadron lepto-production in the current and target fragmentation regions

We study the inclusive production of two hadrons in deep inelastic processes, ?N→?h₁h₂X, with h₁ in the current fragmentation region (CFR) and h₂ in the target fragmentation region (TFR). Assuming a factorized scheme, the recently introduced polarized and transverse momentum dependent fracture functions couple to the transverse momentum dependent fragmentation functions. This allows the full exploration of the fracture functions for transversely polarized quarks. Some particular cases are considered.     

Grain fragmentation in ultrasonic-assisted TIG weld of pure aluminum

Under the action of acoustic waves during an ultrasonic-assisted tungsten inert gas (TIG) welding process, a grain of a TIG weld of aluminum alloy is refined by nucleation and grain fragmentation. Herein, effects of ultrasound on grain fragmentation in the TIG weld of aluminum alloy are investigated via systematic welding experiments of pure aluminum. First, experiments involving continuous and fixed-position welding are performed, which demonstrate that ultrasound can break the grain of the TIG weld of pure aluminum. The microstructural characteristics of an ultrasonic-assisted TIG weld fabricated by fixed-position welding are analyzed. The microstructure is found to transform from plane crystal, columnar crystal, and uniform equiaxed crystal into plane crystal, deformed columnar crystal, and nonuniform equiaxed crystal after application of ultrasound. Second, factors influencing ultrasonic grain fragmentation are investigated. The ultrasonic amplitude and welding current are found to have a considerable effect on grain fragmentation. The degree of fragmentation first increases and then decreases with an increase in ultrasonic amplitude, and it increases with an increase in welding current. Measurement results of the vibration of the weld pool show that the degree of grain fragmentation is related to the intensity of acoustic nonlinearity in the weld pool. The greater the intensity of acoustic nonlinearity, the greater is the degree of grain fragmentation. Finally, the mechanism of ultrasonic grain fragmentation in the TIG weld of pure aluminum is discussed. A finite element simulation is used to simulate the acoustic pressure and flow in the weld pool. The acoustic pressure in the weld pool exceeds the cavitation threshold, and cavitation bubbles are generated. The flow velocity in the weld pool does not change noticeably after application of ultrasound. It is concluded that the high-pressure conditions induced during the occurrence of cavitation, lead to grain fragmentation in a pure aluminum TIG weld during an ultrasonic-assisted TIG welding process.     

微观描述热核裂变寿命（英文）

有关热核裂变的研究与反应堆中的诱发裂变,天体环境中的裂变,以及超重元素的合成等密切相关。热核裂变的研究通常是基于Bohr-Wheeler 的统计裂变理论。而统计模型的研究十分依赖唯像的能级密度和位能面。因此,提出基于微观的有限温度的能量密度泛函理论计算热核的裂变寿命。可以微观自洽地计算出温度相关的裂变位垒高度,曲率,集体质量参数。基于虚自由能法,从低温到高温的裂变寿命可以由一个统一的框架给出。展示了在裂变研究中温度相关裂变位垒的重要性,并讨论了微观描述热核裂变的前景。The studies of thermal fission rates are relevant to novel reactors, astrophysical environments, and survival probabilities of compound superheavy nuclei. This has been conventionally studied by the Bohr-Wheeler statistical model that depends on phenomenological level densities and fission barriers. In this context, we propose to study the thermal fission rates based on microscopic temperature dependent nuclear energy density functional theory. The microscopic temperature dependent fission barrier heights and curvatures, and collective mass parameters can be self-consistently obtained. The fission lifetimes from low to high temperatures can be given by the imaginary free energy method in a consistent framework. Microscopic temperature dependent fission barriers play an essential role in fission studies.     

Isospin dependence of projectile fragmentation and neutron-skin thickness of neutron-rich nuclei

By investigating the cross section distributions of fragments produced in the 140 A MeV ^40,48Ca+⁹Be and 1 A GeV ^124,136Xe+Pb reactions, the isospin dependence of projectile fragmentation in fragment production is studied. In the framework of the statistical abrasion-ablation model, the 1 A GeV ¹³⁶Xe+²⁰⁸Pb reaction is calculated. By adjusting the diffuseness parameter in neutron density distribution of ¹³⁶Xe, we find the isospin dependence of projectile fragmentation in fragment production is sensitive to the neutron-skin thickness of the projectile nucleus.     

Dynamical systems study of chameleon scalar field

The present work is an extensive study of the viable stable solutions of chameleon scalar field models leading to possibilities of an accelerated expansion of the universe. It is found that for various combinations of the chameleon field potential V(?)$V\left(?\right)$ and the coupling f(?)$f\left(?\right)$ of the chameleon field with matter, a stable solution for an accelerated expansion is quite possible. The investigation provides a diagnostics for the stability criteria for all sorts of combinations of V(?)$V\left(?\right)$ and f(?)$f\left(?\right)$.     

Compatibility as underlying mechanism behind the evolution of networks

In this work we propose a dynamic network model based on an evolutive rule called compatibility. The presence of common topological properties observed in two real complex networks are well reproduced by the proposed model. These results suggest that the compatibility between nodes is sufficient to generate the complexity observed in real systems even considering that the new added nodes do not have the ability to know global information of the system.     

Convenient synthesis of stable silver quantum dots with enhanced photoluminescence emission by laser fragmentation

A new strategy for the facile synthesis of very stable and mono-dispersed silver(Ag) quantum dots(QDs) is developed by laser fragmentation of bulk Ag in water using polysorbate 80 as a dispersing and stabilizing agent. The surfactant plays an important role in the formation of size-controlled Ag nano-structures. The Ag QDs have excellent photo-stability of～ 500 h and enhanced photoluminescence(PL) at 510 nm. This has significant implications for selective and ultrasensitive PL probes. Based on laser fragmentation in the biocompatible surfactant solution, our results have opened up a novel paradigm to obtain stable metal QDs directly from bulk targets. This is a breakthrough in the toxicity problems that arise from standard chemical fabrication.