The Simulation Of New EAS Thermal Neutron Detector With Geant4 Toolkit

The formation of the knee region structure of cosmic rays is closely related to the origin,acceleration and propagation of cosmic rays,and it has become a difficult problem in the century.Therefore,it is of great significance for the astrophysics of high-energy particle to make a correct explanation for the cause of formation of the "knee region" of cosmic rays.There are many theoretical assumptions of the origin of "knee region",but the systematic difference between the different experimental results is up to 30%,so it is difficult to make an effective judgment on the theoretical hypothesis of the origin of cosmic rays.The accurate measurements of the composition and energy spectrum of cosmic rays are helpful to solve the problem of "knee region" of cosmic rays and to understand the origin of cosmic rays.The LHAASO-ENDA experiment designed and implemented cooperatively by Hebei Normal University,Tibet University,Sichuan University,Institute of High Energy Physics of the Chinese Academy of Sciences and the Institute of Nuclear Physics of the Russian Academy of Sciences is an array of 16 thermal neutron detectors(EN-detector).The detector array has been successfully built at Tibet University(3650 meters above sea level)in March 2017.The EN-detector can simultaneously measure the electromagnetic composition in the shower and the number of thermal neutrons produced by the core Hadron,which can be used to measure the composition and energy spectrum of cosmic rays in the knee region.The application of thermal neutron detection technology in high altitude cosmic ray measurement to measure the composition and energy spectrum of PeV cosmic rays may provide an important technical basis for solving the physical problems of the energy spectrum of knee region of cosmic rays.Geant4 is a large-scale open source Monte Carlo simulation package developed by the European Nuclear Center(CERN)based on C+language.It can simulate the transmission and interaction of particles in the detector and can be used in nuclear physics and high energy physics experiments.Geant4 provides the interaction between all kinds of particles and matter,which can accurately measure the motion of particles in the medium.It can also define the geometry and properties of various substances.It enriches the interaction model and makes the complex detector structure closer to the experiment.In this paper,the energy deposition in scintillator and the electronic reading of photomultiplier tube are modeled by the photon tracking function of Geant4,and the energy resolution of composite scintillator can be given directly by counting the number of photoelectrons.Based on the toolkit and laboratory measurement results,a new Monte Carlo unit model of EAS thermal neutron detector is constructed in this paper.Comparing the simulation results with the experimental results,the rationality and reliability of the simulation parameters can be verified.The establishment of the simulation program provides a more accurate development tool for the design of a new type of EAS thermal neutron detector.The attempt of this simulation work lays a foundation and accumulates experience for full simulation of a new type of EAS thermal neutron detector array.This paper can be divided into the following parts:The first chapter mainly introduces the cosmic ray thermal neutron detection technology and the application of Geant4 Monte Carlo simulation package.The second chapter focuses on the construction of LHAASO-ENDA experiment and the structure principle of each part,detection process and signal characteristics of the new EAS thermal neutron detector.In the third chapter,the simulation of a new type of EAS thermal neutron detector is introduced,as well as the preliminary results of simulation.The fourth chapter summarized the work of this paper and provide an outlook of the value and contribution of LHAASO-ENDA project to cosmic ray physics.