Effect of the accelerator design on the position of the effective electron source.
An analysis of the effective source-surface distance was made taking into account the influence of energy, field size, equivalent square field size, and the accelerator design. Measurements made in three accelerators showed the influence of parameters like beam flattening and collimation systems on the effective source-surface distance. A brief review of the theory is made leading to a mathematical expression for the effective source-surface distance, showing a good agreement with the experimental results. An alternative method for correcting the dose rate, maintaining the nominal source-surface distance, and not using the inverse square law, but a greater power function, is suggested.