System for monitoring the position intensity uniformity and directivity of a beam of ionizing radiation

In a monitoring system for determining the uniformity of a beam of ionizing radiation and any deviations thereof from a predetermined axis, comprising a radiation detector with a plurality of superposed ionization chambers centered on said axis and separated by radiation-transparent walls, a source of said radiation forming a beam generally centered on said axis, a disk-shaped electrode transverse to said axis in each of said chambers, and circuitry connected to said electrodes for evaluating the relative magnitudes of currents induced by the beam in said electrodes,

• the improvement wherein said electrodes include a first electrode with a diameter significantly less than that of said beam in one ionization chamber and a second electrode with a diameter substantially equal to that of said beam in another ionization chambers, said circuitry including voltage-comparison means provided with input connections modifying the relative magnitudes of voltages proportional to said induced currents by a factor corresponding to the surface-area ratio of said electrodes whereby said voltages are equal upon full illumination of all said electrodes by a homogenous beam.