α preformation and penetration probability for heavy nuclei

The α preformation factor and penetration probability have been analyzed for even-even nuclei of Po,Rn,Ra using experimental released energies and α decay half-lives in the frame of the double folding model.It is shown that N = 126 is a neutron magic number from α preformation and shell effects play an important role in α preformation.The closer the nucleon number is to the magic number,the more difficult α formation in the parent nucleus is.The preformation factor can supply information on the nuclear structure and the penetration probability mainly determines α decay half-life.     

Calculation of α decay half-lives for superheavy elements using the double folding model＊

α decay half-lives of some new synthesized superheavy elements, possibly synthesized superheavy elements and decay products are calculated theoretically within the WKB approximation by using microscopic α-nucleus interaction potentials. These nuclear potentials between the α particle and daughter nuclei are obtained by using the double folding integral of the matter density distribution of the α particle and daughter nuclei with a density-dependent effective nucleon-nucleon interaction, in which the zero-range exchange term is supplemented. The calculated α decay half-lives are compared with those of the different models and experimental data. It is shown that the present calculation successfully provides the half-lives of the observed decays for some new superheavy elements and therefore gives reliable predictions for α decay of possibly synthesized superheavy elements in future experiments.     

Simulation of 12C+12C elastic scattering at high energy by using the Monte Carlo method

The Monte Carlo method is used to simulate the ¹²C+¹²C reaction process. Taking into account the size of the incident ¹²C beam spot and the thickness of the ¹²C target, the distributions of scattered ¹²C on the MWPC and the CsI detectors at a detective distance have been simulated. In order to separate elastic scattering from the inelastic scattering with 4.4 MeV excited energy, we set several variables: the kinetic energy of incident ¹²C, the thickness of the ¹²C target, the ratio of the excited state, the wire spacing of the MWPC, the energy resolution of the CsI detector and the time resolution of the plastic scintillator. From the simulation results, the preliminary establishment of the experiment system can be determined to be that the beam size of the incident ¹²C is φ 5 mm, the incident kinetic energy is 200-400 A MeV, the target thickness is 2 mm, the ratio of the excited state is 20%, the ight distance of scattered ¹²C is 3 m, the energy resolution of the CsI detectors is 1%, the time resolution of the plastic scintillator is 0.5%, and the size of the CsI detectors is 7 cm×7 cm, and we need at least 16 CsI detectors to cover a 0° to 5° angular distribution.     

强脉冲电子束辐照材料表面形貌演化的模拟

在回顾和总结强脉冲电子束表面改性实验的基础上, 利用有限元数值计算方法对强脉冲电子束辐照铝和304不锈钢产生的温度场进行模拟, 给出了靶的近表面区域流体状态存在的特征尺度和特征时间, 并对不同材料特性下熔坑的产生原因进行了讨论. 采用两相流模型, 通过水平集方法和有限元方法结合的计算流体力学模拟了熔坑和表面突起形貌在表面处于熔融状态下的运动特征, 通过和实验数据相对比, 验证了对于高黏度, 高表面张力的高熔点金属, 表面处于流体状态下的张力驱动效应是熔坑等表面形貌演化的重要原因.     

强流脉冲离子束能量密度分布的红外诊断

强流脉冲离子束在靶上的能量密度分布是其研究和应用的一个重要参数。为了解决现有束流能量密度诊断方法的不足,利用红外成像仪测量靶背面的温度分布,从而建立了强流脉冲离子束能量密度分布的红外诊断方法。对能量密度1J/cm2量级、脉冲宽度为102 ns量级的束流,该方法测量误差好于5%,空间分辨率可达到1~2mm,具有操作简便、成本低的优点,是强脉冲能量沉积分布的一种高效迅速的诊断方法。     

Double folding model calculation applied to fusion reactions

The interaction potential between a spherical and a deformed nucleus is calculated within the double-folding model for deformed nuclei. We solve the double folding potential numerically by using the truncated multipole expansion method. The shape, separation and orientation dependence of the interaction potential, fusion cross section and barrier distribution of the system ¹⁶O+¹⁵⁴Sm are investigated by considering the quadrupole and hexadecapole deformations of ¹⁵⁴Sm. It is shown that the height and the position of the barrier depend strongly on the deformation and the orientation angles of the deformed nucleus. These are quite important quantities for heavy-ion fusion reactions, and hence produce great effects on the fusion cross section and barrier distribution.     

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     

Nucleon--nucleon interactions in the double folding model for fusion reactions

Nucleus-nucleus potentials are determined in the framework of double folding model for M3Y-Reid and M3Y-Paris effective nucleon-nucleon(NN) interactions.Both zero-range and finite-range exchange parts of NN interactions are considered in the folding procedure.In this paper the spherical projectile-spherical target system 16O+208Pb is selected for calculating the barrier energies,fusion cross sections and barrier distributions with the density-independent and density-dependent NN interactions on the basis of M3Y-Reid and M3Y-Paris NN interactions.The barrier energies become lower for Paris NN interactions in comparison with Reid NN interactions,and also for finite-range exchange part in comparison with zero-range exchange part.The density-dependent NN interactions give similar fusion cross sections and barrier distributions,and the density-independent NN interaction causes the barrier distribution moving to a higher position.However,the density-independent Reid NN interaction with zero-range exchange part gives the lowest fusion cross sections.We find that the calculated fusion cross sections and the barrier distributions are in agreement with the experimental data after renormalization of the nuclear potential due to coupled-channel effect.     

赝火花脉冲电子束传输中束斑分析

通过赝火花强流脉冲电子束对酸敏变色片和单晶硅的轰击试验，结合束流自箍缩效应进行理论计算，对赝火花脉冲电子束传输中束斑的变形进行了研究与分析. 结果表明椭圆形轰击束斑是由通过旁路电容的瞬态电流产生的方位角磁场所引起的，并且提出了解决束斑变形的有效方法. 关键词： 脉冲电子束 赝火花放电 束斑 自箍缩效应