A new method for the direct measurement of the energy absorption coefficient of gamma rays

The most important primary interaction cross section of gamma radiation which is of interest in radiation dosimetry and health physics is the energy absorption coefficient μen of the medium under study. Direct measurement of μen is, however, difficult and recourse is t aken to theoretical computations for its estimation. In this study a new, simple and direct method for the determination of μen is reported. The method is based on paraxial sphere transmission using a proportional-response gamma detector. The bremsstrahlung originating from photoelectrons in the absorbing medium and fluorescence radiations from shielding etc. have been suppressed by using suitable filters. The effects of nonparaxiality of finite sample thickness have been accounted for, using extrapolation procedures. The deviation from nonproportionality and other corrections have been shown to be small. The measured value of μen for paraffin has been determined as (3.3+-0.2)x10-3 m2/Kg. This compares favourably with the theoretically computed value of 3.35 x 10-3 m2/Kg given by Hubbell et al