Research On CSR External Target Experiment T₀ Detector

The heavy ion Cooler-Storage-Ring (HIRFL-CSR) at Lanzhou is one of the National Important Project on Science. The CSR target is built for heavy ion impact kinetics and the study of radioactive beam. The external target device consists of a gamma detector, a large acceptance poles, a charged track detector, a flight time spectrometer etc. The start-time detector, also known as the To detector, uses the plastic scintillator and the photomultiplier tube (PMT) as the basis in the first phase has realized good performance. However, some of the key characters of the detector can be improved to study physics more precisely, such as time resolution. This paper studies the key problem of using MRPC to construct T0 detector, so as to provide reference for practical design. The research work mainly includes two aspects:1. Studied the MRPC energy deposition problem. Using pi+ and proton incidence,select the incident angle from 0° to 50°, the incident kinetic energy from 100MeV to 900MeV, the energy deposition of particles through monolithic MRPC is studied. The energy deposition of the particles is in the range of 36MeV to 4MeV , The higher energy of the incident particles have, the lower the energy loss is. The mainly energy range of the CSR external target is between 500MeV and 900MeV, the largest energy loss ratio for proton is 2.2%, the largest loss ratio for pi+ is 1.4%, the results will not have much impact to the subsequent detector.2. Simulation of the single layer, cylinder and double three different structure of the T0 detector’s time resolution. According to the particle momentum distribution similar to the energy distribution of the target particles, the mathematical description of the momentum distribution particles is fitted. The random number is taken as the pi+particle’s kinetic energy in Geant4, and calculated according to the time given by Geant4. The time resolution of the T0 detectors of single-layer, cylinder and double-layer is 2.37 ± 0.08ps、2.43 ±0.09ps and 0.306±0.005ps.It can be seen that the time resolution of single-layer and cylinder structure is almost the same, and the double-layer structure is better than the time resolution of single-layer and cylinder structure. It is obvious that double-layer structure can improve T0 precision.In this thesis, the various techniques for T0 detectors are introduced. The advantages of MRPC as T0 detectors are analyzed. The structure and materials of MRPC are described. Based on this, the energy deposition of MRPC is simulated. The time resolution of T0 detector with different structure of MRPC is simulated, and the conclusion is that To detector with double-structure has good time resolution.