| Popis: |
Cosmic ray muon tomography is a developing method based on scattering theory which can be applied in nuclear material discrimination because of its sensitivity to high Z material in recent years[1]. Various muon tomography systems with different kinds of detectors have been set up, such as drift tube [2], Gem [3], RPC [4]/MRPC [5], scintillator strip [6] and drift chamber [7]. Because of the importance of muon energy in material scattering density reconstruction, muon spectrometer of at least two slabs whose size and atom number are known and track detectors has been constructed to provide an estimate of the momentum of each exit muon [8], which may increase the complexity and costs of muon tomography system. In addition to this kind of muon spectrometer, Time of Flight (TOF) method can also be applied to obtain energy. The MRPC detectors employed in TUMUTY (Tsinghua University Cube for Cargo Inspection) [5], developed by Tsinghua University, have both good spatial resolution and time resolution, motivating the thought of muon energy measurement with TOF method [9]. With the muon track and time of flight obtained from 6-layer MRPC detectors, the energy of each muon can be detected. However, as muon travels almost as fast as light, it is not easy to get the muon energy with high accuracy by TOF or muon spectrometer method. Fortunately, accurate muon energy is not necessary in muon tomography [10]. In this paper, the influence of muon energy on material discrimination has been studied and preliminary simulation results indicate that muons with low-energy have more significant influence on the distribution of scattering angles than high energy. Multilayer TOF method has been employed for muon energy segment and the RMS difference between materials of interest becomes larger with the low-energy muons acquired via this method in our simulation, making it easier to distinguish different materials. |
