核耗散强度对角动量的可能依赖性

对130MeV ³He+^natAg→^110,112In和890以及714MeV ⁸⁴Kr+²⁷Al →¹¹¹In反应中的核耗散行为进行了一个比较分析. 数据分析建议除了已知的温度和/或形变依赖性以外, 核耗散强度可能对角动量也存在一定的依赖性.     

角动量和温度对耗散裂变明显触发的影响

对大量中重裂变系统(A>160)实验数据的分析表明:温度和角动量是触发裂变延迟效应的两个最基本条件.In的数据揭示了大角动量条件对轻系统情形的重要性.     

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     

核粘滞性对裂变过程的影响

根据裂变扩散模型,把裂变核的形变运动看成是一种准布朗粒子在裂变势作用下的扩散过程.通过Monte-Carlo方法模拟这种布朗粒子在两维相空间内的运动,研究了核粘滞性对裂变过程的影响;解释了裂变过程中的耗散现象.在各种粘滞系数下,对于裂变速率,断点动能等动力学量的数值计算结果是合理的.此法易于推广用来研究多维扩散问题.     

用He离子诱导的裂变激发函数探测核摩擦强度(英文)

随机模型被用于分析3He+197Au,3He+208Pb和3He 186W反应测量的裂变激发函数。提取的鞍点前摩擦强度约为4×1021s-1。揭示了能级密度参数的大小在约束核摩擦强度中的作用。计算表明,高激发条件能能显著增强裂变截面对核耗散的敏感性。     

同位旋对用裂变截面探测鞍点前摩擦的影响

耦合了轻粒子发射的随机Langevin模型被用于计算三个Bi裂变系统因核耗散效应引起的相对于标准统计模型预计的裂变截面值的变化,σ_fdrop作为激发能的函数。发现209Bi的σ_fdrop要大于202Bi和195Bi的σ_fdrop,这表明高同位旋系统209Bi的裂变截面对摩擦强度有更大的敏感性。该结果建议,当实验上使用裂变激发函数来更精确地提取鞍点前摩擦强度时,应产生具有高同位旋的复合核。进而,通过Langevin计算拟合p+206Pb和p+209Bi反应的裂变激发函数数据,提取的鞍点前摩擦强度为（3~5）×1021 s-1。Langevin models that are coupled with particle emission are applied to calculate the drop of fission cross section caused by friction over its standard statistical-model value, σ_fdrop, as a function of excitation energy for three Bi nuclei with different isospins. We find that σ_fdrop become larger for 209Bi than for 202Bi and 195Bi, indicating a greater sensitivity of fission cross section to friction for high-isospin 209Bi. These results suggest that, to more accurately determine the presaddle dissipation strength by measuring fission excitation functions, it is best to populate those compound systems with a high isospin. Furthermore, we analyze the data of fission excitation functions measured in p + 209Bi and p + 208Pb reactions, which yield high-isospin 210Po and 209Bi systems, and extract a presaddle friction strength of (3-5)×1021 s-1 by comparing Langevin simulations with these experimental data.     

重离子耗散碰撞激发函数的涨落

综述了重离子耗散碰撞激发函数中截面涨落现象的实验与理论研究的现状． The present status of the studies on the cross section fluctuation phynomeno in dissipative heavy ion collisions (DHIC) is reviewed, especially for the fluctuation characteristics and the theoretical deuelopment.     

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.     

高激发核相继裂变的限制

高温核衰变是当前中能重离子核物理中研究最热烈的课题.理论上对高温核的衰变进行了各种预言,相继裂变就是其中之一.本文从有关核裂变的时间尺度、裂前中子发射、裂变截面等随激发能的变化和多重碎裂的实验结果以及复杂碎片发射时间的实验结果分析了对高温核相继裂变的限制,提出了从复杂粒子蒸发向多重碎裂过渡的可能性. Sequential fission is one of the several kinds of theoratical production for hot nucleus de-cay.By analysing relevant experimental results such as fission time scale,prescission neutron emission,fission cross sections and their variation with excitation energy,the results of multifragmentation andthe time scale of complex fragment emission,a limit to the sequential fission of the hot nucleus is sug-gested in this paper.A transition from intermediate mass fragment evaporation to..     

角动量对断前粒子发射壳效应的影响

用Smoluchowski方程研究了角动量对一个轻的闭壳核¹³²Sn裂变前粒子蒸发壳效应的影响,发现壳对断前粒子发射的影响敏感地依赖于这个裂变系统的角动量.对可能的原因进行了讨论     

Roles of Isospin in Evaporation Residue Cross Section as a Probe of Nuclear Dissipation

The influence of isospin on the excess of evaporation residue cross section over its standard statistical-model value for nuclei ^194pb, ^200Pb, and ^206pb is studied via a Langevin equation coupled with a statistical decay model. The magnitude of this excess for a low-isospin fissioning nucleus is shown to be larger and its dependence on the nuclear viscosity coefficient to be stronger than those of a high-isospin fissioning nucleus. These results suggest that to obtain a more accurate information of viscosity coefficient inside the saddle point by measuring evaporation residue cross sections, we had better choose those compound systems with small isospin.     

光束截面的动量守恒及动量衍射发散度

在忽略了瞬逝波的条件下，证明真空中单色标量光场的光束截面的动量及其任一分量都与轴向坐标无关，为守恒量；文中还给出了动量衍射发散度的表达式。     

Influence of angular momentum on evaporation residue cross section as a probe of nuclear dissipation

By calculating the excess of the evaporation residue cross sections of the 200pb nucleus over that predicted by the standard statistical model as a function of nuclear viscosity coefficient using a Langevin equation combined with a statistical decay model, it is found that high angular momentum not only amplifies the dissipation effects on the excess of the evaporation residue cross sections, but also considerably increases the sensitivity of this excess to the nuclear viscosity coefficient. These results suggest that on the experimental side, to accurately obtain the information of nuclear dissipation inside the saddle point by measuring the evaporation residue cross section, it had better populate those compound systems with high spins.     

Influence of angular momentum on evaporation residue cross section as a probe of nuclear dissipation

By calculating the excess of the evaporation residue cross sections of the ²⁰⁰Pb     

同位素分布的标度参量对于两体碰撞的同位旋相关性和动量相关作用的依赖

利用同位旋相关的量子分子动力学模型, 对中能重离子反应产物中的同位素分布进行了研究, 重点分析了平均场中的动量相关作用和两体碰撞的同位旋相关性对于产物中同位素标度现象的影响. 结果表明: 这两个因素均明显减小了同位素标度参量α的值, 从而减弱了同位旋标度参量α对两个反应系统同位旋差的依赖性.     

Remarks on the Total Angular Momentum in General Relativity

We verify that the total angular momentum 3-vector defined by the author [X. Zhang, Commun. Math.Phys. 206 (1999) 137] is equal to (0, 0, ma) forany time slice in both the Kerr and the Kerr-Newman spacetimes.