Dose rate outside primary barriers.

The author has investigated the use of the inverse square function to predict the photon dose rate outside primary barriers for medical accelerators. Measurements of the dose rate as a function of distance outside the barriers were made at five medical accelerator facilities. An analysis of the data showed that the radiation field appears to diverge from a point between the x-ray target and primary barrier. This behavior of the x-ray beam was attributed to scattering of photons in the shield barrier. It was concluded that the dose outside the barrier will be overestimated if the distance from the x-ray target to the point of calculation is utilized to carry out an inverse square correction.