Abstract: System for the detection of substances and in particular explosives, by neutron irradiation thereof.It comprises means (4) for the irradiating, by neutrons, of an object (6) which may contain a substance, means (14) for detecting the gamma radiation which can be emitted by the object and means (18) for processing the signals supplied by the detection means. These processing means count the gamma photons of each line of a plurality of characteristic lines of at least one chemical element of the substance, determining for each line a probability of false detection of the chemical element associated with said line, determine the product of these probabilities, compare said product with a threshold fixed by users and notify the latter if the product is below the threshold, the object then being assumed to contain the substance.

Abstract: According to the invention, the object (34) is brought to a first inspection station (I to IV) in which the object is irradiated by thermal neutrons, the capture gamma radiation then liable to be emitted by the object and characterizing a chemical element of the substance to be detected is detected, if the intensity of said radiation exceeds a predetermined threshold, the object is brought to a second inspection station (V,VI), in which the object is irradiated by fast neutrons and the prompt gamma radiation then liable to be emitted by the object and characterizing the chemical element is detected, the energy of the fast neutrons being at least equal to that of prompt gamma radiation, in order to confirm or disprove the information obtained in the first station.

Abstract: It comprises e.g. a 14 MeV neutron generator for supplying these neutrons to an object liable to contain an explosive, a germanium detector and analysis means coupled to the detector and able to analyse the fast .gamma. photons emitted by the object and trapped by the detector and determine the nitrogen/oxygen ratio in the object, so that this ratio can be compared with that of the explosive and establish whether the object contains said explosive.

Abstract: A device for detecting fissionable material including a neutron source, two parallelepipedal panels placed on a support and forming a dihedral with an adjustable opening. The dihedral has an edge centered on the neutron source, and the panels consist of solid modules made of a material able to thermalize the neutrons and of a module of the same material in which a unit for detecting fission neutrons is housed. This detection unit is located at the end opposite the neutron source, and the object to be checked is placed between the two panels. The device has application to the checking of nuclear waste.