An automatic x-ray isodose plotter.

A radiation detector is made to follow each isodose line in turn and its path is recorded. Polar coordinates are used. The output of the detector is compared with a selected fraction of a fixed reference detector for use with X-ray generators or a DC voltage for isotope sources. If the output from the moving detector is too great, the servo system is arranged to drive the moving detector to a position of lower dose rate, or vice versa if the signal is too small.