中能重离子碰撞中的碰撞参数研究

在入射能量E为40和100MeV/u时,对¹¹²Sn+¹¹²Sn和¹²⁴Sn+¹²⁴Sn两个反应系统在不同碰撞参数下进行了同位旋相关的量子分子动力学模型计算,系统研究了阻塞率、线性动量转移、荷电粒子多重性、轻荷电粒子多重性、中子多重性以及束缚核总电荷Z_bound随碰撞参数的变化规律,结果表明,中子多重性对碰撞参数的依赖在两个能量下都存在着明显的同位旋效应,Z_bound在E为40MeV/u时存在着同位旋效应.同时讨论了在较低和较高能量时如何更合理地确定反应事件的碰撞参数.     

中能重离子碰撞中多重碎裂的同位旋效应

利用同位旋相关的量子分子动力学,研究了逆反应系统¹²⁰Xe+⁴⁰Ca,¹²⁰Cd+⁴⁰Ar和⁷⁶Kr+⁴⁰Ca,⁷⁶Zn+⁴⁰Ar中多重碎裂的同位旅效应.对于在中能区缺中子碰撞系统的中等质量碎片多重性大于丰中子碰撞系统的现象进行了分析和讨论.     

朗之万方程模拟核裂变碎片的同位旋标度

使用结合朗之万方程和统计分支的组合模型模拟¹¹²Sn+¹¹²Sn和¹¹⁶Sn+¹¹⁶Sn两个同位旋相关的反应系统, 通过高斯分布采样的方式得到了核裂变的碎片分布, 将两系统碎片的同位素和同中子异位素的分布相比, 发现存在同位旋标度律现象. 同时提取了同位旋标度系数, 发现同位旋标度系数是和碎片分布宽度相关的, 并且同能量、单位质量的粘滞系数也有很强的依赖关系.     

中能重离子碰撞中同位旋相关核子–核子碰撞截面的灵敏探针

基于重质量弹核(放射性核或稳定核)打轻质量靶核的逆运动学效应,即反应产物主要集中在小角度的优点,利用同位旋相关的量子分子动力学模型,探寻了对于中能重离子碰撞过程中同位旋效应灵敏的物理观测量.计算表明,在入射能量约大于80MeV/u能区,中等质量碎片多重性随发射带电粒子总数之间的演化是提取介质中同位旋相关的核子–核子碰撞截面的灵敏物理量.     

多重碎裂的同位旋效应和动量相关作用的影响

利用同位旋相关的量子分子动力学模型,对中能重离子碰撞过程中多重碎裂对于同位旋自由度和动量相关作用的依赖性进行了研究.结果表明:在相对较高能区,碎片的平均多重性敏感地依赖于介质中核子–核子碰撞截面的同位旋效应,但很弱地依赖于对称势;动量相关作用增强了中等质量碎片多重性对于核子–核子碰撞截面的同位旋依赖的敏感性.中等质量碎片的平均多重性可用作提取介质中同位旋相关的核子–核子碰撞截面的探针.     

中能重离子碰撞中同位旋相关核子–核子碰撞截面的可能观测量

利用同位旋相关的量子分子动力学研究和寻找提取中能重离子碰撞多重碎裂中同位旋相关核子–核子碰撞截面的可能观测量.计算结果表明,在多重碎裂过程中中等质量碎片多重性与带电粒子总数之间的关联是在所选能区提取介质中同位旋相关核子–核子碰撞截面的灵敏观察量.应用重质量弹核打轻质量靶核具有反应产物向前角发射这一逆反应效应,可以在有限探测器条件下与实验相结合提取介质中同位旋相关的核子–核子碰撞截面.     

30MeV/u40Ar+112,124Sn反应中的同位素产额比与核温度

系统研究了30MeV/u ⁴⁰Ar+^112,124Sn反应中的轻粒子同位素产额比随角度和初始激发能的变化关系.对于两个反应体系,均观察到³He/⁴He和⁶Li/⁷Li的产额比随角度的增加而增加,⁶He/⁴He和⁸Li/⁷Li随角度的增加而减小.统计发射的运动学效应不能完全符合实验结果.各种单同位素产额比与靶核的N/Z比有关,表现出同位旋效应,而由双同位素比提取的核温度几乎没有靶核相关性.     

中能重离子同位旋分馏对系统质量和能量的依赖性

利用同位旋相关的量子分子动力学理论,研究了中能重离子碰撞中同位旋分馏强度(N/Z)n/(N/Z)frag对于碰撞系统质量和能量的依赖关系.这里(N/Z)n和(N/Z)frag分别是核子发射 （气相）和碎片发射多重性（液相）的中子-质子比.研究结果表明同位旋分馏强度是反应 系统质量和能量的灵敏函数.当系统同位旋（中子-质子比）入射能量和碰撞参数都固定时, 同位旋分馏强度随系统质量的增加而减少.因为随系统质量的增加与较轻系统比较.重系统具 有大的压缩能,小的热能和大的液-气相变的临界温度.故核子输运过程和同 关键词： 同位旋分馏 对称势     

同位旋对轻系统裂变前粒子发射的影响

在Smoluchowski方程的框架内,研究了同位旋对轻裂变同量异位素源¹¹⁰Tc,¹¹⁰Pd,¹¹⁰In和同位素源^110,117,124In裂变前粒子发射的影响.计算结果表明:断前粒子发射对裂变源的同位旋有很强的依赖性,随着同位旋的增加,中子发射增强,而轻带电粒子则减弱;对一个高同位旋的系统,质子和α粒子不适合作为提取核耗散强度的实验观测量;核耗散强度的大小不改变同位旋对粒子发射的影响规律     

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...     

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.     

Kinetic equation with exact charge conservation.

A kinetic master equation for multiplicity distributions is formulated for charged particles which are created or destroyed only in pairs due to the conservation of their Abelian charge. It allows one to study time evolution of the multiplicity distributions in a relativistic many-body system with arbitrary average particle multiplicities. It is shown to reproduce the equilibrium results for both canonical (rare particles) and grand canonical (abundant particles) systems. For canonical systems, the equilibrium multiplicity is much lower and the relaxation time is much shorter than the naive extrapolation from grand canonical results. Implications for chemical equilibration in heavy-ion collisions are also discussed.     

Surveying post-saddle nuclear dissipation with protons and a particles as probes

Using a Langevin model, we calculate post-saddle proton and a-particle multiplicities as a function of the post-saddle dissipation strength (β) for the heavy systems ~(234)Cf, ~(240)Cf, ~(246)Cf and ~(240)U. We find that, with increasing isospin of the system, the sensitivity of post-saddle light charged-particle multiplicities to β decreases considerably and, moreover, for 240U the charged-particle multiplicities are no longer sensitive to β. These results suggest that in order to determine the post-saddle friction strength more accurately by measuring the multiplicities of pre-scission protons and a particles, it is best to populate those heavy compound systems with low isospin.     

Multiplicity of charged and neutral pions in deep-inelastic scattering of 27.5 GeV positrons on hydrogen

Measurements of the individual multiplicities of and produced in the deep-inelastic scattering of 27.5 GeV positrons on hydrogen are presented. The average charged pion multiplicity is the same as for neutral pions, up to , where z is the fraction of the energy transferred in the scattering process carried by the pion. This result (below ) is consistent with isospin invariance. The total energy fraction associated with charged and neutral pions is (syst.) and , respectively. For fixed z, the measured multiplicities depend on both the negative squared four momentum transfer and the Bjorken variable x. The observed dependence on agrees qualitatively with the expected behaviour based on NLO-QCD evolution, while the dependence on x is consistent with that of previous data after corrections have been made for the expected -dependence. Received: 2 April 2001 / Revised version: 27 June 2001 / Published online: 7 September     

同位旋对断前粒子发射影响的角动量依赖性

对一个同量异位素链²⁰²Fr,²⁰²Po,²⁰²Tl和一个同位素链^189,202,212Po,用裂变扩散模型考察了角动量对裂变前粒子发射同位旋效应的影响.发现断前粒子发射的同位旋效应敏感地依赖于系统的自旋.高的角动量不但弱化了同位旋对粒子蒸发的影响,而且也降低了核耗散对粒子发射的影响.因此,为了更准确地用粒子多重性来提取核耗散系数,选择一个低自旋的复合系统是重要的     

Particle multiplicity of unbiased gluon jets from \mathrme^+\mathrme^- three-jet events

The charged particle multiplicities of two- and three-jet events from the reaction ee Z are measured for Z decays to light quark (uds) flavors. Using recent theoretical expressions to account for biases from event selection, results corresponding to unbiased gluon jets are extracted over a range of jet energies from about 11 to 30 GeV. We find consistency between these results and direct measurements of unbiased gluon jet multiplicity from and Z decays. The unbiased gluon jet data including the direct measurements are compared to corresponding results for quark jets. We perform fits based on analytic expressions for particle multiplicity in jets to determine the ratio of multiplicities between gluon and quark jets as a function of energy. We also determine the ratio of slopes, , and of curvatures, , where y specifies the energy scale. At 30 GeV, we find and , where the uncertainties are the statistical and systematic terms added in quadrature. These results are in general agreement with theoretical predictions. In addition, we use the measurements of the energy dependence of and to determine an effective value of the ratio of QCD color factors, . Our result, (total), is consistent with the QCD value of 2.25. Received: 25 October 2001 / Revised version: 20 January 2002 / Published online: 5 April 2002     

晕核反应机制与内部结构之间的关系

在对中子晕核和质子晕核反应机制研究的基础上, 经仔细分析和对比, 进一步展现晕核反应机制和它的内部结构之间存在着内在的关系. 计算结果分析表明, 由于所选中子晕核¹¹Li的结构比质子晕核²³Al的结构更加松散, 故与²³Al比较,¹¹Li更易碎裂, 因而导致碎片多重性明显增加. 同时由于¹¹Li的松散结构导致两体碰撞过程的减弱, 因而导致动量耗散的减弱, 故与²³Al对比, 将引起原子核阻止明显减少.     

Nuclear interaction of 300 GeV negative poins in emulsion

Experimental data are presented on charged particle multiplicities production in interactions of 300 GeV/c negative poins with emulsion nuclei. Correlations were established and the obtained parameters of multiplicity distributions compared with those obtained from proton-nucleus interaction data at 300 GeV/c.     

e~＋e~－湮没中不同味道夸克喷注带电粒子多重数差别

利用“夸克产生律”与“夸克组合律”计算了ｅ＋ｅ－湮没中重夸克喷注事例的带电粒子多重数，结果与实验符合．并与轻夸克喷注事例及平均夸克味道喷注事例的多重数做了比较．