Concept design and feasibility study of novel calorimeter-type borehole muon detector

Cosmic ray muons are secondary particles produced by the interaction of interstellar protons with the atmosphere. Muons have the characteristics of different angle scattering for different materials and deep penetration in matters, which are helpful in the identification of high-Z substances and the internal density imaging of large targets. In geoscientific research, attenuated transmission imaging of large targets usually employs planar plastic scintillator detectors to record muons tracks. However, due to their large volume, the detector cannot be employed in scenarios where a spacious room is unavailable, such as inside a small borehole. This work proposes a novel calorimeter-type borehole muon detector with a compact structure, fewer electronic channels, decent positional and angular resolutions, and high efficiency. The detector can record the angle of the incident muon. On this basis, imaging of the target object can be realized. This work introduces the principle and concept design of the borehole muon detector, the detector's Monte Carlo simulation study, and the scintillator unit's experimental research. The experimental study of the scintillator unit shows that the position resolution of the position-sensitive detector can reach up to 5.1 mm. The Monte Carlo simulation analysis of the borehole muon detector illustrates that its azimuth angular resolution is similar to 0.103 rad, and the zenith angular resolution is similar to 0.016 rad. The weighted average efficiency of the detector is 64.8%. Simulation results show that the proposed detector is capable of identifying objects with different densities, such as the cavity and the iron sphere, given reasonable measurement duration. This work provides a technical base for the next step of detector design optimization and production.