Radiation exposure in civil aircraft

An active dosemeter based on two silicon planar detectors was flown on civil aircraft Eights to study the altitude and latitude dependence and any potential short-term variations of the radiation exposure. The count rate versus altitude at flight levels FL310-FL410 near Frankfurt (Germany) has been found to be proportional to an exponential law [exp(-x/(175 +/- 10))] where x is the amount of residual atmosphere in g.cm(-2). The latitude dependence at investigated altitudes levels off at latitudes,greater than 60 degrees. No significant short-term variations of the count and dose rates were detected on the flights during quiet times of solar activity. Preliminary mean dose equivalent rates are 3.2 and 1.4 mu Sv.h(-1) for high and low latitude flights respectively. These values are probably lower limits due to the uncalibrated neutron response of the instrument.