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     

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     

100,104Sn核在裂变过程中发射的轻粒子多重性

用扩散模型考察了轻的幻核¹⁰⁰Sn在裂变过程中蒸发的轻粒子多重性. 发现壳仅对质子的发射有很强的影响, 而对中子几乎没有影响, 这与¹³²Sn核的情况正好相反. 因此把这种现象归因于系统中质比(N/Z)的影响. 通过比较¹⁰⁴Sn和¹⁰⁰Sn发射的粒子, N/Z的 影响得到了进一步证实. 计算发现高激发能弱化了N/Z效应.     

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     

垒下16O+232Th裂变碎片角关联模拟

使用Monte-Carlo模拟计算了垒下¹⁶O+²³²Th系统转移裂变和复合核裂变碎片角分布及角关联.转移过程、熔合过程和裂变过程分别用半经典模型、耦合道模型及鞍点过渡态统计模型进行模拟.考虑了各物理量分布产生的运动学效应及裂前中子发射和裂后碎片粒子蒸发对碎片角分布及角关联的影响.模拟结果和实验测量的分布相一致.使用折叠角技术借助Monte-Carlo模拟区分转移裂变和复合核裂变是可能的.考虑了转移裂变和裂前中子发射的影响,复合核裂变碎片角分布各向异性异常仍然存在.     

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.     

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.     

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.     

曲率能及压缩能对缺中子裂变系统断前中子发射的影响

用改进了的动力学与统计相结合的模型, 研究了曲率能及压缩能对\,4\,个缺中子裂变系统: ¹⁸⁸Pt, ²⁰⁰Pb, ²¹³Fr和²²⁴Th的断前中子发射的影响. 计算结果显示用改进模型得到的断前中子多重性相比原来模型的低估要更靠近实验数据. 对于目前工作考虑压缩能的原因进行了讨论.     

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.     

Photoluminescence from surface-oxidized Ge nanoclusters

Photoluminescence from gas-evaporated Ge nanoclusters consisting of a crystalline core encased in an oxide shell are presented. An as-grown sample shows room temperature luminescence with separate peaks around 357 and 580 nm. Prolonged air exposure of the clusters reduces the Ge core dimensions, and the emission initially at 580 nm shifts to 420 nm; however, the violet luminescence at 357 nm displays no difference. These results indicate that there are two mechanisms involved with light emission from Ge nanoclusters, visible light emission associated with the quantum confinement effect, and violet light emission correlated to luminescent centers.     

Influence of Angular Momentum on Shell Effects of Pre-scission Particle Emission of a Light Closed Shell Nucleus 132Sn

Based on the Smoluchowski equations, we study the influence of angular momentum on the shell effects of pre-scission particle emission for a light closed shell nucleus ¹³²Sn. It has been found that the shell effects of pre-scission particle multiplicity depends on the angular momentum in a complicated way. Possible reasons are discussed.     

Pre-formation Probability of 5He Cluster in Pre-equilibrium Mechanism

The possibility of 5He cluster emission has been affirmed theoretically. In order to describe the emission probability of 5He cluster, the pre-formation probability of 5He cluster in pre-equilibrium emission process is needed to be established. In terms of Iwamoto-Harada model, the theoretical formula of pre-formation probability of 5He cluster including 1p shell nucleon in pre-equilibrium mechanism has been established and calculated. In the case of low incident energies, the configuration of [1, m] for 5He cluster is the dominant part in the nuclear reaction. The calculated results indicate that pre-formation probability of configuration [1, m] for the unstable 5He cluster is much smaller than those of d, t, 3He, and 4He, i.e. the light stable composite particles, which are consisted of only 1s shell nucleons. However, it is propitious to the emission of 5He from the point of view on threshold energies, since the binding energies of 5He are generally lower than that of 3He in compound nucleus. The corresponding model formula has been given in this paper for described pre-formation probability of 5He cluster in pre-equilibrium mechanism.     

Trap-state-assisted white light emission from a CdSe nanocrystal integrated hybrid light-emitting diode

This Letter reports on the fabrication of hybrid white-light-emitting diodes made of semiconductor nanocrystals (NCs) integrated on InGaN/GaN LEDs. Using core type and core/shell type CdSe NCs, the white light properties are systematically engineered for white light generation with high color rendering index (CRI). Unlike CdSe/ZnS core/shell NCs, which exhibited a unique narrowband edge emission, core type CdSe NCs offered extended broad emission toward orange/red wavelengths associated with deep trap states. Consequently, the light-emitting properties of the devices showed strong dependence on the type of NCs used, and devices with CdSe NCs offered admirable characteristics, such as Commission Internationale d'Eclairage coordinates of (0.356, 0.330) and a CRI as high as 87.4.     

CdSe/CdS核/壳型纳米晶的光谱特性

以巯基乙酸为稳定剂制备了CdSe/CdS核／壳型纳米晶。用光吸收谱（Abs)、光致发光谱（PL）及光致发光激发谱（PLE）研究了CdS壳层对CdSe纳米晶电子结构，从而对其吸收和发光性能的影响。根据PL和PLE的结果以及带边激子精细结构的计算结果，我们用尺寸很小的纳米晶中所形成的基激缔合物解释了PL光谱与吸收边之间较大的Stokes位移。     

Baryon number violating nuclear decay

The expressions for baryon number violating nuclear partial decay widths are derived from the interactions as predicted by grand unified theories. Theory predicts that the baryon number violating proton decay inside the nucleus is hindered relative to the free proton decay rate. In the case of closed shell nuclei, the meson spin-isospin dependence of the partial width is the same as that for the nucleon decay. The branching ratios of decay amplitudes depend on the nuclear binding energies. Nuclear structure introduces lepton energy spread of ±49.5 MeV for light closed shell nuclei, while it does not affect the back to back emission of lepton-meson pair.