Estimation of dose due to cosmic rays in Japan

Dose rates due to cosmic rays at all municipalities in Japan are estimated using a computer code (PLOTINUS) developed by K. O'Brien. Latitude, longitude and altitude data for all municipalities are assumed to be represented by the location of the city office and categorized into 417 data sets every degree for latitude, every two degrees for longitude, and every 50-m for altitude as input data for computation. The outputs for each cosmic ray component are grouped into two categories, ionizing component including photons and neutron component. The population weighted average dose in Japan is estimated to be 29.2 nSv h-1 for the ionizing component, 6.1 nSv h-1 for the neutron component and 35.3 nSv h-1 for the total. The highest value among prefecture averages is found in Nagano Prefecture to be 44.0 nSv h -1 although it is not located at the highest latitude but at the highest altitude. Based on the assumption in the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2000 Report for dose estimation due to cosmic rays, the doses in Japan are estimated to be 0.21 mSv a-1 for the ionizing component, 0.045 mSv a-1 for the neutron component and 0.26 mSv a-1 for the total. (author)