断前粒子发射的壳效应

用推广的裂变扩散模型研究了裂变前壳效应对粒子发射的影响.双幻核²⁰⁸Pb和¹³²Sn被用作例子来展示这个壳效应.计算结果表明壳效应对这两个复合系统断前发射的粒子有影响.对中子,壳的影响非常明显.我们发现壳对中子发射的影响随着裂变系统激发能的增加而逐渐变弱.     

同位旋对断前粒子发射的壳结构依赖性

用扩散模型研究了壳对幻数附近的核,即²⁰⁴Pb,²⁰⁸Pb,²¹²Pb和¹²⁸Sn,¹³²Sn,¹³⁶Sn,在裂变过程中蒸发轻粒子多重性的影响.发现壳能够影响粒子发射的同位旋依赖性,并且该影响的大小与复合系统的自旋和激发能有关.计算表明角动量在壳影响同位旋相关的粒子发射中起到了显著的作用,而高激发能弱化了壳的影响.     

10.6MeV/u 84Kr+27Al反应中角动量对断点前粒子多重性的影响

用推广的裂变扩散模型研究了角动量对10.6MeV/u ⁸⁴Kr(²⁷Al,二体裂变)反应断点前粒子多重性的影响,发现阶点前粒子多重性和断点时间随着角动量的减小逐渐增大,而且绝大多数粒子是在鞍点前发射的. 对实验中二体裂变反应发生的角动量范围进行权重平均,得到了与实验一致的断点前粒子多重性. 同时还研究了影响断点前粒子多重性和断点时间的诸多因素.     

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     

断前粒子发射的同位素效应

用推广的裂变扩散模型研究了²⁸Si+^164,167,170Er→^192,195,198Pb反应中测量的断前中子、质子和α粒子多重性的激发函数.发现扩散模型能很好地拟合这些轻粒子多重性随裂变系统激发能和Pb同位素的变化趋势.表明断前粒子发射存在一个同位素效应.进而在一个考虑了裂变过程中摩擦效应的统计模型的框架内,在In和Er这两个元素的同位素链中,考察了同位素效应与裂变碎片质量不对称性和裂变系统尺度的关系.计算结果表明:同位素效应的存在不依赖于裂变系统的大小和不对称性.此外,当裂变系统具有高的中质比时,轻带电粒子发射将不再敏感于裂变延迟时间的长短,而中子发射则非常敏感.这个结果暗示对那些特别丰中子的裂变系统,轻带电粒子(质子和α粒子)的多重性对于研究热核裂变过程中的摩擦强度不是一个好的探针.     

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     

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.     

形变对10.6MeV/u 84Kr+27Al反应裂变前粒子发射的影响

研究了形变效应对10.6MeV/u ⁸⁴Kr+²⁷Al反应中断前粒子发射的影响.发现通过测量的裂变前粒子多重性提取的裂变延迟时间将因此从20×10^－21s减少到5×10^－21s,表明增强的断前粒子发射有一部分来自形变效应的贡献.     

转动自由度对10.6MeV/u 84Kr+27Al反应中裂变前粒子增强发射的影响

在统计模型的框架内研究了In核在三维空间的转动自由度对10.6和8.5MeV/u ⁸⁴Kr+²⁷Al碰撞裂变前粒子发射的影响.发现对后一个轰击能,断前粒子发射不敏感于转动自由度;对前一个能量,转动自由度的引入使提取的裂变延迟时间从20×10^－21s减少到7.5×10^－21s,表明了它对裂变前粒子蒸发的影响,计算结果也表明仅有转动自由度并不能完全解释In核的断前粒子增强发射现象.发现了转动自由度在粒子发射中所起的作用对系统的激发能有一定的依赖关系.     

Influence of Isotope on Shell Effects of Pre-scission Particle Evaporation

The shell effects on the particle evaporation prior to fission for three Pb isotopes, 204pb, 20sPb, and 212pb,as well as three Sn isotopes, 128Sn, 132Sn, and 136Sn, are explored by a diffusion model. Calculations show that the magnitude of shell effects in the emission of particles changes with the neutron-to-proton ratio N/Z of these fissioning nuclei, and this change is affected significantly by the spin and excitation energy of the system. It is shown that high angular momentum enhances the dependence of shell effects on the N/Z while high excitation energy weakens such a dependence.     

Influence of Isotope on Shell Effects of Pre-scission Particle Evaporation

The shell effects on the particle evaporation prior to fission for three Pb isotopes, ^204Pb, ^208Pb, and ^212pb,as well as three Sn isotopes, ^128Sn, ^132Sn, and ^136Sn, are explored by a diffusion model. Calculations show that the magnitude of shell effects in the emission of particles changes with the neutron-to-proton ratio N/Z of these fissioning nuclei, and this change is affected significantly by the spin and excitation energy of the system. It is shown that high angular momentum enhances the dependence of shell effects on the N/Z while high excitation energy weakens such a dependence.     

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.     

Influence of Shell on Pre-scission Particle Emission of a Doubly Magic Nucleus 208Pb

Using Smoluchowski equation, we study the shell effects on the emission of light particles in the fission process of a doubly magic nucleus ²⁰⁸Pb. Calculated results show that shell has a considerable effect on the neutron emission and that shell effect gradually becomes weak with increasing excitation energy. In addition, a dependence of shell effects in the neutron emission on the angular momentum has been found.     

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     

形变对断前粒子发射同位旋效应的影响

用动力学与统计相结合的模型和统计模型分别研究了形变对重同量异位素²⁰⁰Ag,²⁰⁰Tl,²⁰⁰Bi和轻同量异位素¹¹⁰Pd, ¹¹⁰In, ¹¹⁰Te断前粒子发射的影响. 计算表明形变的影响是存在的, 但形变却并没有改变中子和带电粒子发射 对系统同位旋的依赖关系. 对可能的原因也进行了讨论.