Monte Carlo Simulation for Background Noise Study of the Wudalianchi Volcano with Cosmic Ray Muons

Abstract

Muon radiography has become a powerful tool to study the volume density of large objects of a few hundred meters scale. However, background noise can reduce significantly the efficiency of this technique if not adequately eliminated. In our muon radiography experiment to image the density structure of the Wudalianchi volcano in northeast China, the muon flux was overestimated due to background noise leading to a serious underestimation of the volcano density. To estimate correctly the level of background noise and propose solutions to reduce it, we use the CRY (cosmic ray shower library) library to generate the cosmic particles (electrons, protons, and muons) and the GEANT4 tool to simulate the interaction of cosmic muons within the volcano structure. The results show that the background noise in muon radiography is mainly made of low-energy particles (less than 2 GeV). To discriminate this background and eliminate it, we study the feasibility of two methods: one is based on using absorbers in front and between the detection layers to stop low-energy particles or to increase their angular deviation so they can be efficiently tagged. The second is based on the Time of Flight (ToF) technique. The two methods aim at separating low-from-high-energy particles. This study will be instructive for our next volcano experiments.