在33.4MeV/u 17N与9Be反应中中子发射的起源

在不同角度测得的33.4MeV/u ¹⁷N+⁹Be反应中,发射中子的能谱具有复杂的形式,而且随着角度的增大显示出有规律的变化.发射中子至少来源于靶弹核间的核子–核子碰撞、¹⁷N的破裂反应以及熔合热核的统计蒸发三种不同起源.分析结果表明:反应体系三种起源的发射中子截面分别为4.49,0.44和5.5b.     

Monte Carlo simulation of the property of a scintillation bar in the multi-neutron correlation spectrometer

To perform a kinematically complete measurement of the dissociation reaction for neutron-rich nuclei, a multi-neutron correlation spectrometer is proposed at Peking University. A Monte Carlo simulation code based on GEANT4 is developed for a single scintillation bar which processes not only the energy deposition but also the light propagation in the scintillator and the light collection and conversion to signal at the end of the bar in a realistic way. The simulating method is described in detail in this paper, and the timing and position resolutions and detector efficiency are studied based on the simulation and compared with the experimental results. A new method of crosstalk rejection has been demonstrated to be important for the design of the whole spectrometer.     

Multi-modal analysis for low energy neutron-induced fission of 235U

Low energy neutron induced fission of 235U is studied in the framework of the multi-modal fission model. The fission fragment properties, such as the yields, the average total kinetic energy distribution and the average neutron separation energy, are investigated for incident neutron energies from thermal to 6.0 MeV. The multi-modal fission approach is also used to evaluate the prompt fission neutron multiplicity and spectra for the neutron-induced fission of 235U with an improved version of the Los Alamos model for incident neutrons below the （n, nf） threshold. The three most dominant fission modes are taken into account. The model parameters are determined on the basis of experimental data. The calculated results are in good agreement with the experimental data.     

17C反应截面和去中子截面

利用日本理化学研究所的放射性束流线RIPS, 测量了能量为79A MeV的¹⁷C在¹²C反应靶上的反应截面, 并同时得到了¹⁷C的移去1个、2个及3个中子的截面; 分别利用有限力程Glauber模型和少体Glauber模型结合壳模型的谱因子分析了反应截面和移去1个中子截面, 研究了¹⁷C的密度分布、结构和价中子布居. 反应截面和中子移去截面是两个相互独立的量, 通过对两者的分析, 都可以得出¹⁷C由芯核¹⁶C和价中子组成, 并且价中子主要处于d_5/2轨道的结论. 总结了现有的碳同位素的反应截面和相互作用截面的工作.     

Iosotopic Distributions of the ^18N Fragmentation Products in Coincidence with Neutrons on Targets ^197Au and ^9Be

We present the experimental isotopic distributions of the ^18N projectile fragmentation products Li,Be,B and C in coincidence with neutrons,as well as the inclusive ones on ^197Au and ^9Be targets.In the framework of the abrasion-ablation model,these distributions are calculated for various nucleon density distributions of the projectile.The comparison with experimental isotopic distributions of the projectile-like fragments in coincidence with neutrons shows that the information on the nucleon density distribution of the ^18N projectile can be extracted.     

25MeV/u 6He+9Be破裂反应的α碎片发射

测量了在25MeV/u 6 He轰击9Be靶的破裂反应产生的α碎片双微分截面及角分布,并在Serber模型的框架下计算了在破裂反应中衍射破裂与擦去过程的贡献,并对结果进行了讨论. 结果表明基于包含衍射破裂和擦去过程的Serber模型可以对6He的直接反应进行较好地描述,擦去过程的贡献远大于衍射破裂的贡献. 相对于6Li而言,6He较大的去2n微分截面源于它的弱束缚特性.     

25MeV/u 6He在9Be靶上引起的双中子转移

报道了经仔细设计的150MeV ⁶He+⁹Be实验,并在质心系大角度处测量¹⁰Be和¹¹Be同位素产物的实验数据.鉴别得到相应于单中子转移的371个¹⁰Be事件,同时观测到了相应于双中子转移的5个¹¹Be事件.由此得到相应微分截面分别为(0.11±0.02)mb/sr(θ_cm≈137.4°)和(1.0±0.7)μb/sr(θ_cm≈133.4°),结果表明在所研究的反应体系中,单中子转移截面要比双中子转移截面约大100倍.在⁶He由⁵He-n和α-2n组成的集团模型下,利用零力程扭曲波玻恩近似(DWBA)的计算程序,在数量级上重现了单、双中子转移反应的实验数据     

RIBLL终端大面积中子探测器阵列研制方案的理论计算

介绍了一种用于丰中子核研究的RIBLL终端大面积中子探测器阵列的研制.利用Geant4软件包对该探测系统的中子探测效率、时间分辨和位置分布等进行了蒙特卡罗模拟,同时对探测器的cross?talk进行了研究.给出了探测器的设计方案.     

25MeV/u 6He在9Be靶上的弹性转移反应研究

报告了25MeV/u ⁶He在⁹Be靶上的弹性散射和弹性转移的实验结果. 用光学模型和一阶DWBA的方法计算了弹性散射和³He集团转移的截面, 计算结果和实验测量基本一致. 计算表明³He在⁹Be中的谱幅度应该明显大于壳模型的理论计算值0.70.     

Elastic Scattering of 6He + p at 82.3MeV/nucleon

Differential cross sections for the elastic scattering of halo nucleus 6He on proton target were measured at 82.3 MeV/u. The experimental results axe well reproduced by optical model calculations using global potential KD02 with a reduction of the depth of real volume part by a factor of 0.7. A systematic analysis shows that this behavior might be related to the weakly bound property of unstable nuclei.