Development of the cosmic-ray muon detection system for probing internal-structure of a volcano

Very high energy cosmic-ray muons penetrating through a mountain enable us to probe internal-structure of volacanoes by using the cosmic-ray muon energy spectrum and the range-energy relation of muons. An improved cosmic-ray muon detection system comprising two segmented detectors with multiplicity cut of the soft components of cosmic ray was developed. The result of the test measurement for the volcano Mt. Asama will be presented.