摘要：We have developed a portable assembly type cosmic-ray muon telescope system with power-effective real-time readings to monitor the internal structure of a volcano.Using this system, we have performed measurements at the Satsuma-Iojima volcano and studied the feasibility of using a continuous flux of cosmic-ray muons over the observation period.The system is based on the measurement of time-dependent muon absorption along different, nearly horizontal paths through a solid body.The rationale is that one can deduce the time-dependent changes in the density distribution of muon absorption in the interior of the object where an absorption variation, i.e., a density path variation, becomes an intensity variation since the muon energy spectrum is exponential or, expressed otherwise, it drops rapidly when the energy threshold increases.The muon telescope, which has a surface area of 1 m2, was installed at the observation point located 1.2 km from the summit crater of Satsuma-Iojima.Muon tracks within scintillator layers in the telescope were analyzed continuously by real-time three-dimensional image processing to measure the level of absorption along different ray paths through the summit crater region.A typical angular resolution of the muon detector of ±16 mrad corresponds to a spatial resolution of ±20 m at a distance of 1.2 km.Our results show the density structure determined in Satsuma-Iojima volcano, Japan, which is located above sea level.A density structure situated above sea level can be analyzed at a resolution that is significantly higher than is possible with conventional geophysical measurements.
关键词：Cosmic ray muon module ;density path variation ;time-dependent muon absorption ;solid body ;density structure
