A solid detector for detecting the presence of ionizing radiation in the noise of the detector crystal. For this purpose, the device provides for the generation, at the moment of each of pulses of the ionizing radiation, of signals which open a gate towards a level selector. The device comprises a semiconductor, provided with microchannels where electrons are multiplied by means of secondary emission, and a collector of the electrons generated in the microchannels. The signals which open the gate are generated by the secondary electrons issuing from the microchannels and picked up by the collector.