Calibration Of PMT's Position Response And Simulation Of μ Detector

Yangbajing (YBJ) International Cosmic Ray Observatory is located at YBJ valley of Tibet with high altitude of 4300 meters, good service supports and the existing advanced international cooperation experiments. On this basis, Large High Altitude Air Shower Observatory (LHAASO) will be promoted at YBJ. LHAASO project is proposed to study Comic Ray origin, Cosmic Ray evolvement and others magnitudes of scientific front problems, where different detection methods and large area of these detectors are required, which will reach the needed sensitivities with hybrid measurements.As a main detectors array in LHAASO, one Kilometer square EAS array consists of 5137 electromagnetic charge detectors(EDs) and 1209 muon detectors(MDs). The current primary studies focus on their optimization of the prototypes of EDs and MDs, as well as their performances. In this thesis, the contributions are presented in two parts, 1) the study of the uniformities of candidate photomultiplier tubes (PMTs) with different sizes; 2) Optimization of Muon detectors'prototypes and their performances.The position response of PMT photocathode is one of the main factors affecting the detector energy resolution. A two-dimensional scanning system is constructed, thus several candidate PMTs are tested for study of their photocathode position responses. Based on Linux system, the control program and DAQ system operate smoothly, which benefits the scanning experiments. The analysis results show that different kinds of PMTs show different position responses and the position response is caused by the photoelectron collection efficiency due to focus electrode and electric field distribution inside the PMT, which are useful to the selections of PMTs used in EDs and MDs.The optimization of Muon detectors'prototypes benefits from a GEANT4-based simulation package, where many key parameters were considered, such as water absorption length, Tyvek's reflectivity and the characteristics of PMTs. By restraining the punching-through effects, in the current optimization,the sizes of Muon detector, such as its diameter and height, and the height of the convertor (dirt) on the top of MDs are shown in detail. A small MD prototype has been installed and tested for a long time in our Lab to study its performances in case of single muon. The results are consistent with the simulation ones. In addition, the variation of MDs'performances and water quality were monitored and studied. All the above efforts will be useful and necessary to study the optimization of MDs in further step.