AbstractThe dose distributions in a phantom man exposed to monodirectional electromagnetic radiation in the energy range 0·02 to 1·25 MeV are calculated as a function of incident fluence. This procedure is consistent with established practice in neutron dosimetry. The calculations are performed by a Monte Carlo technique whereby 30,000 photon histories are followed down to a cut-off energy of 10 keV.The results are used to derive the integral over the mass of both dose and dose squared. Dose to the gonads and other organs in several radiation fields are calculated and compared with experimental data. The critical organ is thus identified and the possibility of designing a “risk” meter based on these data is noted.