A detector of ionizing radiation comprises a photodetector and a scintillator in the shape of truncated cone comprising a large base, a small base and a lateral surface, the large base of the scintillator being coupled to the photodetector, any half-angle at the apex of the cone being in the range between 5° and 35°, the lateral face being coated with a black coating. The detector in accordance with an embodiment can produce a very short pulse.