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Abstract. The aim of this study is to ascertain and confirm the source of background noise in cosmic-ray muon radiography (muography) using emulsion film detectors. For this, we build two types of emulsion detectors with different momentum thresholds and perform test measurements of an actual geoscientific target. This experiment reveals that contamination of nonsignal particles with momenta of less than 2 GeV c −1 cause significant systematic errors for the density estimation of muography. Utilizing the results of precedent studies, we conclude that the origin of these low-momentum particles is either electromagnetic components of air showers or cosmic-ray muons scattered in topographic material. In this paper, we analyze the emulsion data in detail, including the film-inefficiency compensation and momentum selection by applying an upper bound to the chi-square distribution for the data.

A new method of momentum measurement of charged particles through multiple Coulomb scattering (MCS) in the OPERA lead-emulsion target is presented. It is based on precise measurements of track angular deviations carried out thanks to the very high resolution of nuclear emulsions. The algorithm has been tested with Monte Carlo pions. The results are found to