Verification of cosmic neutron doses in long-haul flights from Japan

International Commission on Radiological Protection recommends that aircraft crew and frequent flyers be informed of their individual doses received from cosmic radiation onboard aircrafts. The cosmic radiation dose in aviation is generally assessed by model calculations. In Japan, the code “JISCARD EX” is used since 2007 for management of cosmic radiation exposure of aircraft crew. In the present study, the precision of this code was investigated in regard to neutrons which contribute the most to the effective dose in aviation. Measurements of cosmic neutrons were performed with two moderator-type neutron monitors having different response functions: a conventional-type rem meter (NCN1) and an extended energy-range rem meter (WENDI-II) in four long-haul flights to Singapore, Sydney, Washington, D.C. and London from Japan (Narita or Kansai airport). Through the combined analyses of these measurements, the contribution of high-energy (>15 MeV) neutron component was estimated. The ambient dose equivalents, H*(10), measured with WENDI-II agreed well with the calculations made by JISCARD EX, while the contribution of the high-energy component obtained as the difference between the measured H*(10) values of two monitors was systematically higher than the model calculations.