Evaluation of Geomagnetic Latitude Dependence of the Cosmic-ray Induced Environmental Neutrons in Japan

Abstract

A series of precise measurements of the cosmic-ray induced neutron energy spectra have been performed to assess the natural background neutron dose rate in whole Japan. The energy spectra were measured in two regions with different altitudes and geomagnetic latitudes, Hokkaido (northernmost main island) and Kagoshima (southernmost main island), by means of a multi-sphere neutron spectrometer, so called the Bonner Sphere (BS). The total neutron fluence rate, the ambient dose equivalent rate H*(10) and the effective dose rate in isotropic geometry were obtained from the measured neutron energy spectra, and the dependence of these dose rates on geomagnetic latitude was also evaluated.