Spectral characterization of 4 MV Bremsstrahlung by attenuation analysis

The "quality of radiation" for a high energy x-ray beam can be specified by its attenuation curve in a selected material. The inverse Laplace transform of the attenuation curve can be used as an approximate indication of the energy spectrum of the beam. Existing mathematical procedures for this purpose have been evaluated and were found to poorly represent measured transmission data for 4 MV x-rays from a linear accelerator. The transmission data between 1 and 0.002 could be fitted within the experimental uncertainty by expressing the logarithmic transmission as a second order polynomial of attenuator thickness. The inverse Laplace transform them becomes a Gaussian function of the attenuation coefficient. This new version of "attenuation analysis" provides a practical method for specification of the quality of the radiation in this energy range.