Image-detector for high energy photon beams

Image-detector for depicting differences in intensity in high energy photon beams with the aid of a photon-sensitive element, comprising an ionization chamber, two substantially equivalent plates of an electrically insulating material, attached to each other by a ring-shaped electrically insulating divider, the outer walls of both plates being covered with electrically conductive material, one of the plates equipped with a number of parallel high voltage electrodes over a central part of its inner wall and the other plate equipped over a central part of its inner wall with a number of parallel ionization current electrodes extending perpendicular towards the high voltage electrodes, the inner walls of both plates around the central parts being covered with an electrically conductive material, and a liquid dielectric being situated in the space between the plates wherein the high voltage electrodes are provided with voltage separately and in a previously determined series of electrode voltage combinations with the aid of a controlled high voltage selector system, such that currents by the ionization current electrodes are separately measured with the aid of a multi-channel electrometer amplifier circuit.