Application of the photon-fluence scaling theorem to absorbed dose calorimetry for bremsstrahlung peak energy >1.02 MeV

Application of the 'photon fluence scaling theorem' allows the ionization chamber to be placed at points in media where the photon fluence is the same, hence eliminating problems with energy response. The theorem is applicable to Compton scattered photons. For photon energies greater than 1.02 MeV, pair production alters the photon fluence in such a way as to invalidate the scaling theorem. In this report the effect of pair production is examined, so that a correction may be applied to the photon fluence scaling theorem. This correction extends application of the theorem for bremsstrahlung spectra up to at least 25 MeV peak energy. 10 refs., 4 tabs., 1 fig