Estimation of Cosmic Ray Dose in Airplanes with Pocket Dosimeters

INTRODUCTION For the purpose of dose control of aircrew, many dose measurements have been conducted in airplanes. In IRPA-9, we had reported data mainly obtained with a NaI(Tl) scintillation spectrometer(1). In the present study, however, analyses were done on data of pocket dosimeters (Silicon detectors: Aloka PDM-101 for ionizing components and PDM-303 for neutrons). As the pocket dosimeters are compact and easy to handle, their uses are certainly advantageous to collect numbers of data with small efforts. However, commercially available pocket dosimeters are designed for monitoring of nuclear facilities, and particle radiation is fully detectable only when the detector’s volume is large. Therefore, doses indicated by such small pocket dosimeters are not true, and adequate conversion procedures are necessary. Many studies have been done which seek relative dose contributions of neutrons and ionizing components. Researchers of the Institute of Physical and Chemical Research conducted measurements of neutrons on board a chartered airplane in 1975, which covered throughout Japan, giving neutron dose rate of 0.38 μSv/h at 9,450m altitude and 0.083 μSv/h at 4,880m altitude. Simultaneously, they measured dose rate of ionizing components giving 0.941 μSv/h at 9,450m altitude and 0.212 μSv/h at 4,880m altitude. Combined these, the neutron dose contribution was estimated to be 40.4% at 9,450m altitude and 39.2% at 4,880m altitude, respectively. Their conclusion was that the typical neutron dose contribution would be about 40% of ionizing components’(2). However, attention is necessary that the report was made before ICRP Publication 60(3), so that the contribution of 40% should be translated to 80% now.