Muographic data analysis method for medium-sized rock overburden inspections

Abstract. Muographic measurements of rock overburdens are of particular interest because they can be applied to natural resources and undiscovered cave explorations, and even to searching for hidden chambers in historic architectural structures. In order to derive the absolute density distribution of the overburden, we conventionally needed to know accurate information about the measurement conditions, e.g., the detector's geometrical acceptance, detection efficiency, and measurement time, in order to derive the absolute value of the transmitted muon flux. However, in many cases, it is not a simple task to accurately gauge such conditions. Open-sky muon data taken with the same detector are useful as reference data to cancel these factors; however, if the detector is not transportable, this data taking method is not feasible. In this work, we found that the transmitted muon flux will follow a simple function of the areal density along the muon path as long as the incident muon energies are below a few hundred GeV. Based on this finding, we proposed a simple analysis method that does not require detailed knowledge of the detector's conditions by combining the independently measured density information for the partial volume of the target. We anticipate that this simple method is applicable to future muographic measurements of rock overburdens.