Radiation Protection Dosimetry 7:185-189 (1984)
© 1984 Oxford University Press
Indoor Gamma and Cosmic Ray Exposure Rate Measurements Using a GE Spectrometer and Pressurised Ionisation Chamber
Indoor exposure rates due to the penetrating components of the natural radiation field have been measured with a portable germanium gamma ray spectrometer and a pressurised argon ionisation chamber. The ion chamber gives a direct measure of the total exposure rate (gamma plus cosmic radiation), while the spectrometer provides an independent estimate of the gamma exposure rate alone. This estimate is arrived at by first stripping the gamma ray spectrum of events corresponding to only partial absorption in the detector. The resultant total absorption spectrum is converted to flux incident at the detector which is then used to compute exposure in air. The appropriate stripping and flux conversion parameters were determined by calibrating the detector for both full absorption peak and partial absorption continuum efficiency for parallel incident flux. The gamma ray spectrum is also used to measure the uncollided flux from the various lines of the 238U series, 232Th series and 40K to infer their relative contributions to the total exposure rate. Results obtained so far in a variety of buildings demonstrate the utility and sensitivity of the method.