Étude de la Dose au Voisinage de l'Interface entre deux Milieux de Composition Atomique Différente exposés aux Rayonnement γ du 60Co

Ionization measurements in the vicinity of a carbon/metal interface, using gamma rays from 60Co, have made possible the determination of the dose absorbed by a water-equivalent medium in contact with a body of higher atomic number. In the neighbourhood of the interface an extremely rapid dose variation was found, characterized by the occurrence of peaks at a distance of about 20-40 mg/cm2 behind the interface. At the interface between a metal and a water-equivalent medium the dose is smaller than that in water, except for media of very high Z (>75); at the interface between a water-equivalent medium and a metal the dose within the metal is greater than that in water as long as Z is <40. The interpretation of these phenomena is based on the analysis of the contributions made to the electron flux by the electrons originating in the front and in the back medium and which either have or have not undergone back-scattering in the other medium. A comparison of the ionization within various media and of the corresponding absorption coefficients shows that for gamma rays from 60Co and for the condition studied, the mean energy of the electrons which form the electron flux in equilibrium state is of the order of 10 kev.