Characterisation of neutron-sensitive bubble detectors for application in the measurement of jet aircrew exposure to natural background radiation

Abstract

A survey of the natural background dose equivalent received by Canadian Forces aircrew was conducted using neutron-sensitive bubble detectors (BDs) as the primary detection tool. Since this study was a new application for these detectors, the BD response to neutron dose equivalent (RD) was extended from thermal to 500 MeV in neutron energy. Based upon the extended RD, it was shown that the manufacturer's calibration can be scaled by 1.5±0.5 to give a BD sensitivity that takes into account recently recommended fluence-to-neutron dose equivalent conversion functions and the cosmogenic neutron spectrum encountered at jet altitudes. An investigation of the effects of systematic bias caused by the cabin environment (i.e., temperature, pressure and relative humidity) on the in-flight measurements was also conducted. Both simulated and actual aircraft climate tests indicated that the detectors are insensitive to the pressure and relative humidity variations encountered during routine jet aircraft operations. Long term conditioning tests also confirmed that the BD-PND model of detector is sensitive to variations in temperature to within ±20%. As part of the testing process, the in-flight measurements also demonstrated that the neutron dose equivalent is distributed uniformly throughout a Boeing 707 jet aircraft, indicating that both pilots and flight attendants are exposed to the same neutron field intensity to within experimental uncertainty.