Unified fission model for proton emission

The unified fission model (UFM) combining with the phenomenological assault frequency has been carried out to investigate the proton-radioactivity half-lives of spherical proton emitters. The results are in good agreement with the experimental data and other theoretical values, and newly observed spherical proton emitters have been analyzed. Finally, the effect of angular momentum transfer on half-life of proton emission has been discussed in detail and a formula can be used to describe this relationship.     

Two-proton radioactivity of ground and excited states within a unified fission model

A unified fission model is extended to study two-proton radioactivity of the ground states of nuclei, and a good agreement between the experimental and calculated half-lives is found. The two-proton radioactivity half-lives of the ground states of some probable candidates are predicted within this model by inputting the released energies taken from the AME2020 table. It is shown that the predictive accuracy of the half-lives is comparable to those of other models. Then, two-proton radioactivity of the excited states of ¹⁴O, ^17,18Ne, ²²Mg, ²⁹S, and ⁹⁴Ag is discussed within the unified fission model and two analytical formulas. It is found that the experimental half-lives of the excited states are reproduced better within the unified fission model. Furthermore, the two formulas are not suitable for the study of two-proton radioactivity of excited states because their physical appearance deviates from the mechanism of quantum tunneling, and the parameters involved are obtained without including experimental data from the excited states.     

Light-charged particle emission in fission

The emission of light charged particles in the fission process is of interest as they are believed to emerge from the neck region of the deformed fissioning nucleus at a time close to the scission point and may thus prove a useful probe to investigate the last stages of fission close to the rupture point. Experimental results on light charged particle emission and the efforts made to obtain information about the scission point parameters therefrom are reviewed.     

Theoretical study on spherical proton emission

The proton radioactivity half-lives of spherical proton emitters are investigated within a generalized liquid drop model(GLDM),including the proximity effects between nuclei in a neck and the mass and charge asymmetry.The penetrability is calculated in the WKB approximation and the assault frequency is estimated by the quantum mechanism method considering the structure of the parent nucleus.The spectroscopic factor is taken into account in half-life calculation,which is obtained by employing the relativisti...     

Studies of light-charged particle emission in fission at Trombay

Studies of prompt radiations emitted in fission were started at Trombay in the late 1950’s by Dr R Ramanna and over the years extensive investigations on the emission of prompt neutrons, gamma ray and K x-rays in fission were carried out with neutron beams fromapsara andcirus reactors. In the early 1960’s studies on the emission of light-charged particles in fission, which is a rare mode of fission, were also started. This paper reviews some of the recent studies on the emission of light-charged particles (lcp) in fission which were carried out with a view to investigate the mechanism oflcp emission, the scission configuration and the dynamics of the last stages of the fission process.     

Pre-scission particle and gamma-ray emission in heavy-ion-induced fission

An introduction is given to the physics of the equilibrium transition-state model and of dissipative nuclear dynamics. Experimental data on pre-scission particle and gamma-ray emission and their interpretation are reviewed. They appear to indicate overdamped motion of the nuclear fluid. A time scale for compound-nucleus fission of about 30 × 10⁻²¹ s or greater is indicated, whilst that for quasi- or fast-fission is somewhat shorter.     

重核大集团发射半衰期的计算

重核大集团（¹⁴C-³⁴Si）发射的半衰期在理论上用Wentzel-Kramers-Brillouin近似进行了计算.利用双折叠模型计算大集团和剩余子核间的核相互作用,在折叠积分中选取了密度依赖的、零力程交换项的核子-核子相互作用.计算得到的半衰期和液滴模型结果、系统公式的结果以及实验数据进行了比较,表明目前的计算能够很好地给出重核大集团（¹⁴C-³⁴Si）发射的寿命.这可为重核其他大集团（¹⁵N, ⁴⁶Ar,⁴⁸Ca等）的发射提供可靠的预测. 关键词： 半衰期 双折叠模型 集团发射     

Distinction between pre-formed cluster emission and heavy ion decay by fission

For studying cluster radioactivity in the actinide region as well as trans-tin region two types of models are used: the pre-cluster formation model and the unified fission model. In the case of the actinide region, the cluster-like shapes are preferred for very high asymmetry while fissioning shapes are more suitable for less asymmetry and symmetry (the line of demarcation being around A _c =31). In this work this line of demarcation is studied in the case of the trans-tin region. The results of this study show that the transition from cluster mode to fission mode takes place at A _c =16.     

中子诱发232Th裂变初始碎片质量及动能分布Monte-Carlo研究

随着第四代反应堆以及先进核能利用系统的发展,对中子核数据提出了高精度、多核素、宽能区的新要求.目前,中国核数据评价库(CENDL库)中相关核裂变的数据较缺失,不足以满足当前核能发展的需求.因此,建立面向中子核数据需求的可靠计算方法和工具变得极为重要.本文基于Monte-Carlo方法建立了裂变碎片质量动能计算模型,研究了中低能中子诱发²³²Th(n,f)反应发射中子前裂变碎片的分布特性.对于裂变碎片质量分布,本模型计算结果与实验值最大偏差约1%,与GEF, TALYS程序计算结果 (与实验值最大偏差约2%)相比具有一定优势.对于发射中子前裂变碎片动能分布,本模型计算结果与实验数据一致.结果表明,所发展的计算模型能够较好地预测²³²Th(n,f)反应发射中子前裂变碎片数据,为中子诱发锕系核裂变反应计算提供一种新思路.     

Multiparameter studies of polar emission in 236U fission

The energy distributions and relative intensities of protons, deutrons, tritons and α-particles emitted along the fission axis during thermal neutron fission of ²³⁵U were measured simultaneously with both fission fragment energies. The mass distributions of fragments, the total kinetic energy (TKE), the dependence of the mean TKE on the fragment mass, as well as the mean kinetic energy dependence of polar particles on the fragment mass and energy were subsequently deduced from these data. Although some experimental results agree remarkably well with the hypothesis that polar particles are evaporated in flight from fission fragments, the general conclusion is that these particles are emitted according to some other mechanism.     

~(252)Cf自发裂变中子发射率符合测量的回归分析

~(252)Cf同位素源具有标准的自发裂变中子能谱,但由于其半衰期较短,应用中常需要对源强进行标定修正.随着源年龄增加,来自源中~(250)Cf和~(248)Cm自发裂变的影响愈加凸显,不能简单按~(252)Cf的衰变规律计算源中子发射率,而通过锰浴活化的间接测量方法周期较长,且在源强低于10~4 n/s时误差较大.最近,基于中子多重性计数的源强绝对测量算法已得到验证.本文进一步从点模型假设的测量方程出发,在将符合计数率与总中子计数率关联的基础上,分别对符合计数率随源位置、符合门宽的变化关系进行回归分析,提取变化过程的特征系数,建立了两种避规效率变化的~(252)Cf中子发射率测量方法,并基于JCC-51型中子符合测量装置开展实验验证.结果表明:两种回归分析方法的测量值均与标称值的修正结果在2%的偏差范围内一致;反推求得装置中轴线上的探测效率也与基于MCNPX程序的蒙特卡罗模拟计算值相符.研究结果可为活度信息不明的~(252)Cf源强标定及符合测量装置的效率刻度提供便携准确的实验方法.     

二次电子发射对质子束流测量精度的影响

二次电子发射直接影响法拉第探测器测量质子束流的精度,减小或消除二次电子发射的影响是提高束流测量精度的关键。根据二次电子补偿原理设计了二次电子补偿型同轴法拉第探测器,实验发现探测器测量质子束流强度时不能完全实现二次电子补偿。为改进和完善探测器的设计,从理论上分析了补偿片未能完全消除二次电子对束流测量影响的原因,是由于补偿片前向发射二次电子数目大于收集极后向发射二次电子数目所致。为此设计了质子束穿过金属箔发射二次电子测量装置,测量得到能量为5~10 MeV质子穿过10 m厚铜箔时前向与后向发射二次电子产额,验证了理论分析的正确性。     

二次电子发射对质子束流测量精度的影响

二次电子发射直接影响法拉第探测器测量质子束流的精度,减小或消除二次电子发射的影响是提高束流测量精度的关键。根据二次电子补偿原理设计了二次电子补偿型同轴法拉第探测器,实验发现探测器测量质子束流强度时不能完全实现二次电子补偿。为改进和完善探测器的设计,从理论上分析了补偿片未能完全消除二次电子对束流测量影响的原因,是由于补偿片前向发射二次电子数目大于收集极后向发射二次电子数目所致。为此设计了质子束穿过金属箔发射二次电子测量装置,测量得到能量为5~10MeV质子穿过10μm厚铜箔时前向与后向发射二次电子产额,验证了理论分析的正确性。     

Systematics of asymmetry in fission based on order-disorder model

According to Order-Disorder Model (ODM), in the early stages of fission, the charges in a fissioning nucleus gets polarised into two impending parts along with corresponding most stable neutrons which are calculated from the minimum in isobaric mass parabola. This polarisation into two most stable configuration leaves a small number of neutrons as balance neutrons i.e.N _bal. The distribution of theseN _bal for various polarisation modes, shows a very profound correlation with the yield distribution. Judging from this striking correlation between these two distributions, it can be predicted that the asymmetry in fission decreases gradually and ultimately disappear for nuclei havingZ ⋍ 102 but reappears again for the nuclei in super heavy region.     

Cascade-exciton model analysis of level density parameter dependence in proton induced fission cross sections of some sub-actinide nuclei

Fission cross sections strongly depend on the ratio of the level density parameter in fission to neutron emission, a_f/a_n. In this work, a cascade-exciton model implemented in the code CEM95 has been used to observe this effect for proton induced fission cross sections of tungsten, lead and bismuth. The method was employed using different level density parameter ratios for each fission cross section calculation. The calculated fission cross sections are compared with the available experimental data in the literature. It has been observed that a change of the ratio of the level density parameter, a_f/a_n, is necessary with the incident energy of the proton, to best estimate the fission cross sections in CEM95.     

Systematics on fission fragment mass distribution of neutron induced 235U fission

Based on the neutron induced fission fragment mass distribution data up to     

The 6He emission accompanying the spontaneous fission of 252Cf

The results of a multiparameter investigation of the ⁶He emission accompanying the spontaneous fission of ²⁵²Cf are presented. The energy spectrum and the yield of the ⁶He particles are found to be in accord with previous measurements, but their angular distribution is observed to be narrower at 13° ± 3° (FWHM) than the value of ? 32° deduced in a previous investigation.Comparisons of the experimental with published calculated energy spectra and angular distributions for ³H, ⁴He and ⁶He particles are shown to provide evidence for a compact scission configuration in ternary fission.     

Released energy formula for proton radioactivity based on the liquid-drop model

In this work, based on the liquid-drop model and considering the shell correction, we propose a simple formula to calculate the released energy of proton radioactivity(Q_p). The parameters of this formula are obtained by fitting the experimental data of 29 nuclei with proton radioactivity from ground state. The standard deviation between the theoretical values and experimental ones is only 0.157 Me V. In addition, we extend this formula to calculate 51 proton radioactivity candidates in region 51≤Z≤83 taken from the latest evaluated atomic mass table AME2016 and compared with the Q_p calculated by WS4 and HFB-29. The calculated results indicate that the evaluation ability of this formula for Q_p is inferior to WS4 while better than HFB-29.     

Empirical formulas for proton decay half-lives:Role of nuclear deformation and Q-value

Two empirical formulas for the proton decay half-lives including nuclear deformation are proposed. The formula with parameter set I gives the logarithm of the proton decay half-lives as an explicit function of the orbital angular momentum with eight adjustable parameters, whereas that with set II represents the logarithm of the reduced half-lives as an implicit function of the angular momentum with seven adjustable parameters. Experimental data for the half-lives of 44 proton emitters in the ground state or isomeric state were used to obtain the parameters. The experimental and calculated Q values were used. Different sets of parameters were obtained for the ground state transition, isomeric state transition, and all transitions for both deformed and spherical nuclei. The best agreement with experimental data was observed for set I for deformed proton emitters with experimental Q values.