密度分布对原子核阻止同位旋效应的影响

利用同位旋相关的量子分子动力学（IQMD）模型,分析了中能重离子碰撞过程中相对论平均场和SkyrmeHartrere－Fork等核结构模型给出的核密度分布对原子核阻止的影响。研究表明,从费米能到的较大能量范围内,无论小质量体系还是大质量体系,原子核阻止对同位旋相关的核子－核子碰撞截面都非常灵敏,而不同模型给出的核密度分布对原子核阻止影响不大,说明原子核阻止作为提取同位旋相关核子－核子碰撞截面的灵敏探针是与原子核结构模型无关的。 Influence of densitydistributionwhichisgivenbyRMFandSkyrme－Hartrere－Fork etalnuclearstructuremodelonnuclearstoppinginheavy－ioncollisionsatintermediateenergiesarestudiedbyusingisospin－dependentquantummoleculardynamics(IQMD)model.ResearchshowsthatrangeformtheFermienergytothelargerenergyof 100 Mev/u, for bothsmallandlargemasssystem,nuclearstoppingisfoundtobestronglydependentonthenucleon－nucleoncrosssections,andweaklyondifferentdensitydistribution.ThisshowsthatnuclearstoppingcanbeusedasaprobetoextracttheinformationontheisospindependenceN－Ncrosssectionsandhasnorelationshipwithnuclearstructuremodels.     

用中子晕弹核探寻同位旋非对称核物质状态方程

总结和评述了用中子晕弹核探寻同位旋非对称核物质状态方程。 在具有同位旋和动量依赖的同位旋相关量子分子动力学框架内, 采用对比中子晕弹核和相等质量稳定弹核在完全相同入射道条件下物理观测量的差别, 来突出中子晕核明显的同位旋效应和加强物理观测量对于同位旋的灵敏性, 从而提取核物质状态方程。 例如, 与稳定弹核碰撞系统相比, 中子晕弹核明显提高了发射核子的中子\|质子比和增加了它对于对称势的灵敏性, 这两点特征非常有利于提取对称势。 同样, 由于中子晕弹核碰撞系统在低能区（E<60 MeV）由于内部松散结构减弱了核子碰撞力度和动量耗散, 与稳定核碰撞系统相比, 明显提高了原子核阻止; 而在高能区由于两体碰撞同位旋效应的增加, 从而明显提高了原子核阻止。 利用这些特征可以提取核子\|核子碰撞截面的介质效应和同位旋依赖性。 Based on the isospin and momentum dependent quantum molecular dynamics, we use the comparison for the differences between observables in the reactions induced by the halo\|neutron projectile and stable projectile with the same mass under complete same incident channel condition to protrude the isospin effect of halo\|neutron projectile and strengthen the sensitivity of observable on the isospin for extracting the information for the equation of state. For example, the halo\|neutron projectile increases the emitted neutron\|proton ratio and then enhances its sensitivity on the symmetrical potential. Two points above are more favorable than the normal neutron\|rich and neutron\|poor projectiles for extracting the symmetry potential. We also found that the neutron\|halo projectile induces the decrease of nuclear stopping in lower beam energy region and the increase in higher beam energy region, compared to corresponding same mass stable projectile under the same incident channel condition, so that we can use these properties to extract the information for the medium effect and isospin effect of in\|medium nucleon\|nucleon cross section.     

Isospin splitting of nucleon effective mass and symmetry energy in isotopic nuclear reactions

Within an isospin and momentum dependent transport model, the dynamics of isospin particles(nucleons and light clusters) in Fermi-energy heavy-ion collisions are investigated for constraining the isospin splitting of nucleon effective mass and the symmetry energy at subsaturation densities. The impacts of the isoscalar and isovector parts of the momentum dependent interaction on the emissions of isospin particles are explored, i.e., the mass splittings of m_n~*=m_p~* and m_n~* m_p~*(m_n~* m_p~*). The single and double neutron to proton ratios of free nucleons and light particles are thoroughly investigated in the isotopic nuclear reactions of ~(112)Sn+~(112)Sn and ~(124)Sn+~(124)Sn at incident energies of 50 and 120 MeV/nucleon, respectively. It is found that both the effective mass splitting and symmetry energy impact the kinetic energy spectra of the single ratios, in particular at the high energy tail(larger than 20 Me V). The isospin splitting of nucleon effective mass slightly impacts the double ratio spectra at the energy of 50 MeV/nucleon. A soft symmetry energy with stiffness coefficient of γ_s =0.5 is constrained from the experimental data with the Fermi-energy heavy-ion collisions.     

α发射数可作为提取同位旋相关平均场的灵敏探针

利用同位旋相关的量子分子动力学, 对中能重离子碰撞过程中的α发射数的同位旋效应进行了分析。 研究表明, α发射数强烈地依赖于同位旋相关平均场的影响, 而与同位旋相关核子 核子碰撞截面的依赖较弱, 可以作为提取同位旋相关平均场信息的灵敏探针。 由于实验上α粒子发射数的观测比较容易, 而且在很宽地能量范围内, 无论丰中子系统还是缺中子系统都较好地满足上述规律, 这样就可以通过实验上对α发射数的探测, 来提取介质中同位旋相关平均场的信息。 同时建议由实验对缺中子系统的质子发射数进行探测, 从中提取同位旋相关核子 核子碰撞截面的信息。 The α emissions in heavy ion collisions at intermediate energies are studied by using isospin dependent quantum molecular dynamics model. The number of α emitted is found to be strongly dependent on the isospin dependent mean field and weakly on the nucleon nucleon cross sections. The number of α emitted is easy to be measured in experiment and the above conclusion is still available no matter in neutron rich systems or in neutron deficient systems in a wide energy region, so it can be used as an excellent probe for extracting information of the isospin dependent mean field. After several years searching, some information of the isospin asymmetry equation of state has been obtained in theoretically. We suggest to investigate the number of α emitted in neutron rich systems and the number of proton emitted in neutron deficient systems experimentally to obtain more information of the isospin dependent mean field and the isospin dependent nucleon nucleon cross section.     

高动量分布对核反应中原子核的阻止本领的影响

利用同位旋相关的量子分子动力学模型研究了中能重离子碰撞过程中,具有不同中质比的中等质量核碰撞系统的高动量分布对原子核的阻止本领的影响,以及这种影响随入射能量的演化。研究结果表明:对于76Kr+76Kr,88Kr+88Kr碰撞系统,当入射能量较小时高动量分布对原子核的阻止本领影响很小;但当反应能量较大的时候,高动量分布对原子核的阻止本领影响较大,且这种影响随着入射能量和碰撞核质量的增大而增大。对于Ca同位素链的反应系统,高动量分布增大了反应系统的原子核的阻止本领。因此,高动量分布对中等质量核碰撞系统的原子核的阻止本领有重要影响,且与入射能量和碰撞核质量密切相关。Based on the isospin-dependent quantum molecular dynamics model, the effect of high momentum distribution on nuclear stopping in medium mass nuclear collision system is studied with different neutron-proton ratio in intermediate energy heavy ion collisions, and the evolution of this effect with the incident energy. The results show that when the incident energy is small, the high momentum distribution has little effect on the nuclear stopping. However, when the reaction energy is large, the high momentum distribution has a great influence on the nuclear stopping and the influence increases with the increase of incident energy and the mass of collision nucleus. For the Ca isotopes reaction system, high momentum distribution increases the nuclear stopping of the reaction system. Therefore, high momentum distribution has an important influence on nuclear stopping in medium mass nuclear collision system, and closely related to the incident energy and the mass of collision nucleus.     

中能重离子碰撞中同位旋效应的灵敏探针

在重离子碰撞过程中, 基于重质量的弹核轰击轻质量靶核有大量中等质量碎片向前发射的逆运动学效应, 利用同位旋相关的量子分子动力学观察和研究了重离子碰撞过程中同位旋效应的灵敏性． 计算结果表明在所选能区, 中等质量碎片的多重性与带电粒子总数之间的关联是提取介质中核子 核子碰撞截面的灵敏观测量, 而此时对称势的同位旋效应却不明显． Based on the revers kinetic intermediate energy heavy ion collision in which much more intermediate mass fragments are emitted towards forward angles, a sensitive observable on isospin effects in heavy ion collisions is investigated by means of using isospin dependent quantum molecular dynamics (IQMD). The calculation results show that the correlation between the multiplicity of intermediate mass fragments N IMF and total number of charged particles N c is...     

Isospin Effect of Coulomb Interaction on Nuclear Stopping in Intermediate Energy Heavy Ion Collisions

Nuclei offer an interesting isospin situation where symmetry potential, Coulomb term and isopin dependent nucleon-nucleon collisions are simultaneously present. However, in general, Coulomb potential is not studied in the heavy ion collisions. As we know that the Coulomb potential is an important asymmetry term which can bring important isospin effect into the observable in the intermediate energy heavy ion collisions. Recently extensions by Colonna et al.[1] to finite nuclei show that Coulomb and surface effects reduce instability regions. So in this paper the isospin effects of Coulomb term and symmetry potential on the nuclear stopping at intermediate energy heavy ion collisions are studied by using isospin-dependent quantum molecular dynamics model (IQMD).     

中能重离子碰撞过程中同位旋分馏的特征和机制

利用同位旋依赖的QMD模型主要对中能重离子碰撞中同位旋分馏机制和主要特征进行了讨论和分析， 得到了一些有趣的结果， 并建议将同位旋分馏强度作为提取同位旋相关平均场和建立同位旋不对称核物质状态方程的探针. The degree of isospin fractionation is measured by (N/Z)gas / (N/Z)liq，where (N/Z)gas and (N/Z)liq are the saturated neutron proton ratio of nucleon emissions ( gas phase) and that of fragment emitted (liquid phase) in heavy ion collision at intermediate energy. The calculated results by using the isospin dependent quantum molecular dynamics model show that the degree of isospin fractionation is sensitive to the neutron proton ratio of colliding system. In particular， the degree of isospin fractionation sensitively depends on the symmetry potential and weakly on the in medium nucleon nucleon cross section for the neutron rich system. In this case， we propose that the degree of isospin fractionation can be directly compared with the experimental data so that the information about symmetry potential can be obtained.     

Dependence of Isospin Fractionation on Beam Energy in Heavy Ion Collisions at Intermediate Energies

We investigated the dependence of isospin fractionation degree (N/Z)n/ (N/Z)Nfrag on the beam energy by using the isospin dependent quantum molecular dynamics model (IQMD). The (N/Z)n and (N/Z)Nfrag are the neutron proton ratio of nucleon emission (gas phase) and that of fragment emission (liquid phase) respectively. The calculated results show that (N/Z)n / (N/Z)Nfrag enhances with increasing the beam energy due to the increase of excitation energy of colliding system. But above properties is only occurred in the definiteenergy region.     

动量相关作用在原子核阻止作为探针中的重要性

最近的研究工作表明原子核阻止强烈地依赖于两核子碰撞截面而较弱的依赖同位旋相关的平均场 (对称势 ) .故原子核阻止可以作为提取介质中同位旋相关核子 -核子碰撞截面的探针 .详细的计算表明动量相关作用在提高原子核阻止对两体碰撞的敏感性和减弱对称对称势的敏感性中起了重要作用. The role of momentum dependence equation of state on the nuclear stoppings coming from the isospin dependence of nucleon-nucleon cross section (two-body dissipation ) and the isospin dependence of the mean field (one-body dissipation) are studied by using the isospin dependence quantum molecular dynamics. A detail studies indicate that the difference between the nuclear stoppings coming from the isospin dependence and the isospin independence of in-medium nucleon-nucleon...     

Covariance analysis of an isospin-dependent probe

Based on a modified quantum molecular dynamics model,we calculate the neutron-proton ratio and the nuclear stopping of reaction systems with different symmetry potentials and collision cross sections.We perform correlations of several probes using the covariance data processing method.It is shown that the correlation between the nuclear stopping and the isospin-dependent nucleon-nucleon cross sections is strong,but the nuclear stopping and symmetry potentials have a weak correlation.The correlation between neutron-proton ratio and symmetry potentials in the case of low energy is stronger.The correlation between neutron-proton ratio and isospin-dependent collision cross sections is enhanced with the increase of energy,but remains weak.In addition,the correlations of the emission numbers of the deuteron with the symmetry potentials and collision cross sections at different beam energies are not obvious compared to two prior physical quantities.In this paper,we define a parameter to quantitatively describe the sensitivity of isospin-dependent probes.By analyzing this parameter,one can extract more information about the isospin effects of the physical quantity.     

原子核的反常宇称能谱研究

将具有负宇称的 fp 空间扩大到包含1g9/2 轨道, 采用修正的表面相互作用(MSDI), 对64Ge, 66Ge, 68Ge, 70Se, 72Se, 74Se, 76Kr 和 78Kr等偶偶核作了形变Hartree Fock计算, 得到了基态和一些激发态的解. 同时, 还用近似角动量投影形变Hartree Fock（PDHF）方法对偶偶核64Ge, 74Se和奇A核79Kr进行了能谱计算, 得到其正、 负宇称带的解, 计算结果与实验谱基本一致.Using modified surface delta interaction, enlarging the fp configuration space to include the 1g9/2 orbit with the abnormal parity, the deformed Hartree Fock calculations for the eight nuclei: 64Ge, 66Ge, 68Ge, 70Se, 72Se , 74Se, 76Kr and 78Kr are performed. The ground state and some particle hole excited configurations are obtained. The approximate angular momentum projected deformed Hartree Fock (PDHF) method is applied to even even nuclei 64Ge and 74Se and odd A nuclus 79Kr. Both of their normal and abnormal parity bands are obtained. The calculated energy spectra are consistent well with experimental spectra.     

260～520 keV Krq+ (8≤q≤17)离子轰击Al靶产生的可见光辐射

低速高电荷态离子与金属表面相互作用,原子从靶材表面溅射,其中一部分处于激发态的溅射原子通过辐射退激产生可见光。在这一相互作用过程中,低速高电荷态离子从靶材表面捕获一个或多个电子进入其激发态,这些处于激发态的入射离子也会通过辐射退激产生可见光。研究表明,离子在靶材中的核阻止本领与溅射原子产额密切相关。为了更好地理解溅射原子的激发过程,认识低速高电荷态离子与金属相互作用过程中,溅射原子的激发概率与入射离子动能和势能之间的关联,研究了260～520 keV Krq+ (8≤q≤17)离子与Al靶相互作用过程中的可见光发射。给出了520 keV Kr13+ 与Al表面相互作用过程中,发射300～550 nm波长范围的发射光谱。实验结果包括溅射的Al原子在309.0和395.9 nm处的共振跃迁,Al+和Al2+分别在358.3和451.6 nm处的共振跃迁,以及Kr+在430.0,434.1,465.8和486.0 nm处的共振跃迁。还给出了谱线强度比值Y(309.0)/Y(395.9),Y(358.5)/Y(395.9),Y(452.8)/Y(395.9)随入射离子动能和势能的变化。结果表明：谱线强度比值均随入射离子动能的增加而增大,而比值Y(309.0)/Y(395.9)随势能的增加而减小。分析表明,在低速高电荷态离子与Al靶相互作用过程中,动能（电子阻止本领）和势能共同作用导致Al原子的激发,与激发态Al(4s)相比,电子布居较高激发态Al(3d)的概率随着离子电子阻止本领的增加而增大,而随着离子势能增加而减小。在低速高电荷态离子与金属表面相互作用过程中,入射离子在靶材中的核阻止本领影响溅射原子产额,而电子阻止本领与激发概率相关。在这一作用过程中,动能和势能共同决定溅射原子的激发概率,当动能和势能在同一数量级时,动能作用比势能作用小两个量级。     

Fragment distribution in ~(78,86)Kr+~(181)Ta reactions

Within the framework of the isospin-dependent quantum molecular dynamics model, along with the GEMINI model, the ~(86)Kr+~(181)Ta reaction at 80, 120 and 160 MeV/nucleon and the ~(78)Kr+~(181)Ta reaction at 160 MeV/nucleon are studied, and the production cross sections of the generated fragments are calculated. More intermediate and large mass fragments can be produced in the reactions with a large range of impact parameter. The production cross sections of nuclei such as the isotopes of Si and P generally decrease with increasing incident energy.Isotopes near the neutron drip line are produced more in the neutron-rich system ~(86)Kr+~(181)Ta.     

Optimizing the rapidity limit for nuclear stopping in intermediate energy heavy-ion collisions

A systematic study regarding the role of participant matter and spectator matter in nuclear stopping using isospin-dependent quantum molecular dynamics model is presented. The simulations have been carried out with soft equation of state along with the reduced isospin-dependent cross section to study the effect of different types and sizes of rapidity distributions on nuclear stopping for the whole colliding geometry with density-dependent symmetry energy. In addition to that, we attempt to investigate the role of isospin in heavy-ion collisions by calculating the individual contribution of neutrons and protons in nuclear stopping for different systems having different isotopic content.     

Nuclear stopping as a probe for in-medium nucleon-nucleon cross sections in intermediate energy heavy ion collisions

Using an isospin-dependent quantum molecular dynamics, nuclear stopping in intermediate heavy ion collisions has been studied. The calculation has been done for colliding systems with different neutron-proton ratios in beam energy ranging from 15 MeV/ u to 150 MeV/ u. It is found that, in the energy region from above Fermi energy to 150 MeV/ u, nuclear stopping is very sensitive to the isospin dependence of in-medium nucleon-nucleon cross section, but insensitive to symmetry potential. From this investigation, we propose that nuclear stopping can be used as a new probe to extract the information on the isospin dependence of in-medium nucleon-nucleon cross section in intermediate energy heavy ion collisions.     

Systematic Study on System Size Dependence of Global Stopping: Role of Momentum-Dependent Interactions and Symmetry Energy

Using the isospin-dependent quantum molecular dynamical model, we systematically study the role of symme- try energy with and without momentum-dependent interactions on the global nuclear stopping. We simulate the reactions by varying the total mass of the system from 80 to 394 at different beam energies from 30 to 1000 Me V/nucleon over central and semi-central geometries. The nuclear stopping is found to be sensitive towards the momentum-dependent interactions and symmetry energy at low incident energies. The momentum-dependent interactions are found to weaken the finite size effects in nuclear stopping.     

On nuclear stopping in asymmetric colliding nuclei

Using the isospin-dependent quantum molecular dynamics (IQMD) model, nuclear stopping is analyzed in asymmetric colliding channels by keeping the total reacting mass fixed. The calculations have been performed by varying the mass asymmetry of the colliding pairs with different neutron-proton ratios at an incident beam energy of 250 MeV/nucleon. We find sizable effects of mass asymmetry on nuclear stopping and on the equilibrium of the nuclear matter. A reasonable agreement is also observed between the experimental data and our present calculations.