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: A system applicable to the detection of particle radiation for the suppression of noise and its variations for the detection of a pure signal in a measured noisy discrete signal detects events appearing in a predetermined energy window. It carries out a count N.sub.2 for a time .DELTA.T.sub.s and a count N.sub.3 for a time .DELTA.T.sub.b, in which .DELTA.T.sub.b =q..DELTA.T.sub.s and q is a positive number, during which no event corresponding to the expected pure signal is present. It then evaluates the information supplied by counts N.sub.2, N.sub.3 for the chosen value of the coefficient q, or the associated false detection probability, by comparison with at least one information threshold I.sub.m, each threshold being associated with a predetermined false detection level. Comparison takes place indirectly as a function of the probability and uses tabulated values.

Abstract: A system for the suppression of noise and its variations for the detection of a pure signal in a measured noisy discrete signal. The system measures a counting rate N.sub.2 in a signal channel and a counting rate N.sub.3 in a reference channel, evaluates the estimation value .lambda..sub.E of the ratio .lambda. between the mean noise levels in the channels and evaluates the associated false detection probability I as a function of (N.sub.2, N.sub.3 .lambda..sub.E). The system then performs a comparison of I with at least one information threshold I.sub.m, each associated with a predetermined false detection level. Comparison can take place indirectly on a function of the probability and can use tabulated values. The system has particular application to the detection of corpuscular radiation.

Abstract: A system for detecting the presence of a pure signal in a discrete noisy signal measured at a constant average noise level M, having a processor for measuring a counting rate N and for calculating a false detection probability PF as a function of the counting rate and an estimated average noise level M, and for comparing the probability with a predetermined false detection level TF. A pure signal is detectd when the probability is below the false detection level.