【作者】 刘龙祥；

【导师】 肖国青； 陈熙萌； 孙志宇；

【作者基本信息】 兰州大学 ， 粒子物理与原子核物理， 2013， 博士

【摘要】 三体Borromean晕核碎裂反应是现代核物理研究的一个热门领域之一。本文描述了一种标准相空间分布的三体Borromean晕核碎裂模型,并且建立了一套蒙卡模拟方法来解决碎裂反应中产生的双中子在中子墙上的探测问题。模拟使用的工具是Geant4,这是模拟闪烁体探测器的一个理想的软件。为了证明模拟方法的可靠性,我们先做了宇宙射线在中子墙中响应的模拟,然后将模拟结果与已有的实验结果进行比较,以确定模拟中使用的某些参数并说明模拟的可靠性。在做双中子模拟之前,我们先模拟了单个中子在中子墙上的响应,并得出一套分析单个中子事例的方法。然后,再将此方法推广到双中子的事例。通过单中子模拟及分析,我们得到了重建中子的位置、角度及能量精度。以300MeV/μ的6He为例,通过三体模型产生的双中子在中子墙上响应的模拟,我们得到了中子墙探测器激发能重建的误差及探测效率随激发能大小的变化(其中包含立体角接受度)。我们还讨论了算法对碎裂产生的碎片之间的角关联和能量关联的影响,分析结果与探测到的结果总体符合的很好,因此使用的分析方法是可靠的。这为以后中子墙的实验做好了准备。中子墙是一个由多个模块组成的探测器系统,所以普通的刻度方法并不适用。文中介绍了一种利用宇宙射线刻度中子墙的方法。刻度中使用的是前沿甄别器,因此,对时间刻度进行了能量校正。通过时间刻度与位置刻度彼此相互校正,我们还得到了时间与位置误差分布谱,并且比较了宇宙射线在两种不同模块的中子条中的实验与模拟的能量沉积谱。更多还原

【Abstract】 The Borromean halo nucleus breakup reaction is one of the most important and interesting topics in modern nuclear physics. The model of three-body Borromean halo nucleus breakup was described by using standard phase space distribution and the Monte Carlo simulation method was established to resolve the detection problem of two neutrons produced from breakup reaction on the neutron wall detector. The Monte Carlo simulation in this paper is based on Geant4, it is an ideal framework for modeling the scintillator detectors and its associated light guides.Prior for us to engage in detailed MC simulations, the reliability of available computer codes had to be evaluated. We studied the response function of the neutron wall for comic rays with Geant4simulation. Comparison of results from experiments with those from simulations showed that Geant4could be fully relied on for our detector simulation. At the same time, some parameters in the simulation were to be determined by us.We studied the response function of the neuron wall for one neuron with Geant4simulation before two neutrons. Methods for finding the correct neutron incident position and time were discussed, and the neutron position, emit angle and energy were re-constructed and compared with the simulation. The method would be appropriated by the analysis of the two neutrons’ simulation.The three-body breakup6He→4He+n+n was studied as an example by simulation, using300MeV/μ6He ion according to the model’s distributions with selected excitation energies. In the simulation, the response of the neutron wall was obtained by the two neutrons based on the three-body Borromean halo nuclei breakup model. We discussed the distribution of the efficiency and resolution with regard to the excitation energy of6He. The agreement between the detected events distributions and the reconstructed ones after the analysis is reasonably good at the most of the selected energies. Therefore, the algorithm to disentangle two neurons impinging onto the neutron wall is reliable, which could be helpful for the experiments with the detection of neutrons at the external target experiment hall in the future. Calibration of the neutron wall can be performed using interactions of cosmic radiation which presents a natural source of signals. The leading edge discriminator was used in the calibration, so the time signal was corrected by using amplitude-timing correction. The time and position resolution were obtained after the correction between time and position calibration, and we compared of the deposited energy distribution in different kinds of neutron paddle from experiments with those from simulations.更多还原