[Dose rate constant and radial dose function of an iodine 125 radiation source in various substances]

The dose distribution around an isotropic, point radiation source can be expressed by the dose rate constant, the quadratic law of distance, and a radial dose function which depends on the absorption and scatter processes occurring in the surrounding material. The radial dose function and the dose rate constant of a point iodine-125 source can be represented in a clear and rather exact manner as simple functions of the linear attenuation and energy absorption coefficients, because the average photon energy does not considerably vary with the growing distance from the source. This representation is in contrast with some functions defined in a distance of 1 cm, in conformity with the definition of the dose rate constant in the air according to DIN 6814, part 3.