Development of an emulsion imaging system for cosmic-ray muon radiography to explore the internal structure of a volcano, Mt. Asama

A simple particle detection system comprising an emulsion cloud chamber was developed as a potential apparatus for cosmic-ray muon radiography of a volcano. A successful radiographic measurement of the internal structure of Mt. Kama-yama through Mt. Maekake-yama is described. We analyzed the data and the bulk density of 2.25±0.040.06 g cm−3 was determined in Kama-yama. Using the value of the density of the mountain, we confirmed that the volume occupancy in the shallow region of a crater (at a place between the crater rim and 100 m below the rim) is 8.1-8.1+45.9%. We discuss the future perspective of the power-free radiographic imaging device for understanding and monitoring volcanic activity.