弹核碎裂反应的同位旋标度率及核的对称能系数研究

用统计擦碎模型对中能区弹核碎裂反应中的同位旋标度率现象进行了系统研究. 发现在弹核碎裂反应中存在同位旋标度率现象, 但同位旋标度率参数随每核子的激发能的增加迅速下降. 而影响同位旋标度率参数变化的最主要的因素是由于激发能不同及蒸发效应. 采用费米气体模型的激发能与核温度的关系, 从同位旋标度率参数提取出核的对称能系数, 值的大小及其与激发能的变化趋势跟实验数据基本一致.     

GaAs颗粒镶嵌薄膜的非线性光学性质研究

采用单光束的Z扫描技术研究了GaAs颗粒镶嵌薄膜的非线性光吸收和非线性光折射特性,获得了增强的三阶光学非线性响应.实验测得的非线性折射率系数为 10^-3esu和非线性光吸收系数为10^-1cm/W量级.研究了产生饱和吸收时的光跃迁选择定则,观察到了饱和吸收现象和双激子态的双光子吸收现象,实现其饱和吸收和双光子吸收所需的辐射光强小于10⁴w/cm²结果表明:增强主要起源于量子限域效应,在强限域条件下,库仑作用效应被更强的限域作用所掩盖.GaAs颗粒表现出类似于二能级系统的光学非线性响应特征.     

Isospin dependence of projectile fragmentation and neutron-skin thickness of neutron-rich nuclei

By investigating the cross section distributions of fragments produced in the 140 A MeV ^40,48Ca+⁹Be and 1 A GeV ^124,136Xe+Pb reactions, the isospin dependence of projectile fragmentation in fragment production is studied. In the framework of the statistical abrasion-ablation model, the 1 A GeV ¹³⁶Xe+²⁰⁸Pb reaction is calculated. By adjusting the diffuseness parameter in neutron density distribution of ¹³⁶Xe, we find the isospin dependence of projectile fragmentation in fragment production is sensitive to the neutron-skin thickness of the projectile nucleus.     

第一性原理无核芯壳模型计算原子核谱因子

原子核谱因子表征原子核单粒子轨道的性质以及占据数等信息,是联系核结构、核反应与核天体物理的重要物理量。 对于原子核谱因子的计算强烈依赖于理论模型得到的原子核多体波函数,在实际计算中通常选用普通壳模型。随着计算机性能的提高以及核多体方法的发展,第一性原理方法被应用于研究原子核性质,并取得巨大成功。 本工作基于现实两体相互作用,利用第一性原理无核芯壳模型计算较轻原子核谱因子。首先,计算了$A =6$和$7$原子核的低激发态能量,考察第一性原理无核芯壳模型对能量计算的收敛性,并比较普通壳模型与第一性原理无核芯壳模型对于$A =6$和$7$能谱的描述。结果表明,无核芯壳模型计算结果与实验符合较好,可以很好地描述结合能和激发谱性质。 然后,利用无核芯壳模型系统计算了$^{7}{\rm{Li}}$与 $^7{\rm{Be}}$镜像核叠积函数与谱因子,并分析谱因子计算的收敛性。结果显示,谱因子随着模型空间的增大收敛较慢,对于$^{7}{\rm{Li}} $,无核芯壳模型计算的谱因子同最新实验值符合得很好。最后,采用无核芯壳模型系统计算$A =6,\, 7$和$8$原子核低激发谱能量与谱因子,为核反应与核天体研究提供必要的输入量。     

Symmetry energy from neutron-rich fragments in heavy-ion collisions, and its dependence on incident energy, and impact parameters

The yields of fragments produced in the 60Ni+ 12C reactions at 80 A and 140 A MeV, and with maximum impact parameters of 1.5, 2 and 7.3 fm at 80 A MeV are calculated by the statistical abrasion-ablation model. The yields of fragments are analyzed by the isobaric yield ratio (IYR) method to extract the coefficient of symmetry energy to temperature (asym/T ). The incident energy is found to influence asym/T very little. It’s found that asym/T of fragments with the same neutron-excess I = N-Z increases when A increases, while asym/T of isobars decreases when A increases. The asym/T of prefragments is rather smaller than that of the final fragments, and the asym/T of fragments in small impact parameters is smaller than that of the larger impact parameters, which both indicate that asym/T decreases when the temperature increases. The choice of the reference IYRs is found to have influence on the extracted a sym /T of fragments, especially on the results of the more neutron-rich fragments. The surface-symmetry energy coefficient (bs/T ) and the volume-symmetry energy coefficient (bv/T) are also extracted, and the bs/bv is found to coincide with the theoretical results.     

Temperature of Heavy Fragments in Heavy-Ion Collisions

The heavy fragments in heavy-ion collisions are finally formed after the hot prefragments undergo sequential decay,of whom the temperature should be much lower than that of prefragments.Using the double ratio(DR) method,the isotopic thermometer(Tiso) for heavy fragment is constructed using the yield of heavy isotopes.T iso of heavy fragment is obtained by analyzing the measured data in the 1A GeV124,136Xe and 140A MeV 48Ca/64Ni reactions.Result shows that T iso varies from 0.5 MeV to 10 MeV.But most T iso is around 1±0.5 MeV,which is much lower than temperature of light particles.Result also indicates that the difference between T iso of heavy fragments in different reactions is very small,and T iso is independent on the size of the reaction system,the incident energy and the neutron-richness of the projectile.     

渐近保持PIC算法在等离子体粒子模拟中的应用

针对准中性Vlasov-Poisson系统中多尺度物理参数共存的问题开展研究,采用渐近保持格式推导出与Vlasov方程相耦合的Poisson方程。数值模拟了一维等离子体在真空中的膨胀,比较了渐近保持PIC算法与传统PIC算法模拟结果的异同。结果表明：两种算法在满足多尺度中小尺度量限制的前提下,其结果保持高度一致;且在克服小尺度量束缚时,渐近保持PIC算法依然可以正确地模拟等离子体的物理行为,大大节省了计算时间。     

半浮栅晶体管Marx方波脉冲电源设计

为得到工业需要的大电流高重频方波脉冲,分析并改进了半导体全控型Marx发生器,在充电的同时实现了截尾功能。设计采用新型半浮栅结构晶体管 (SFGT)作为主开关,可产生kV高压、百A大电流、高重频的方波脉冲。优化了电路结构,解决直流充电源受脉冲电源放电电压冲击问题。研制得到电流100 A、频率4 kHz、脉宽4 s、负高压6 kV、上升沿下降沿均在80 ns内的方波脉冲发生器。研究了相应的SFGT磁芯隔离驱动电路,结合了SFGT栅极并联自主电容隔离驱动和IR2110的半桥驱动电路,并对半桥上的MOS管的栅极等效电路进行了理论分析,驱动电路具有抗干扰能力强且脉宽调节范围大的特点。     

p+56Fe散裂反应中同位素产生截面的规律现象

提出一个经验公式,预测散裂反应中同位素产生的截面值,并且利用现有GSI-FRS实验测量的300,500,750,1 000和1 500 MeV/u能量下p+56Fe散裂反应产物的实验结果进行验证。发现此经验公式预测的同位素截面值与实验值的符合度比较好,但随着质量数与能量的改变,同位素产生截面的计算值与实验值的差距也在变大。通过引入质量与能量修正可使此经验公式计算出的同位素截面值的精确度更高,与实验值的符合程度更好。An empirical formula is proposed to predict the isotopic cross section in spallation reactions. The measured fragments in the 300, 500, 750, 1 000 and 1 500 MeV/u p+56Fe spallation reactions have been adopted to perform the analysis. The cross sections of isotopes predicted by the proposed empirical formula have been compared to the experimental results, which shows that the empirical formula can predict the results well. But with the change of the mass and incident energy, the difference between the calculated results and experimental data is larger. The proposed empirical formula is found to predict the isotopic cross sections better, by incorporating the incident energy and mass dependents of fragments.