A method for detecting an explosive in an object under investigation involves the initial X-
ray irradiation of the object under investigation, e.g. a piece of luggage or mailing, and forming its X-
ray images; using the X-
ray images to detect areas with a
high density of organic materials and identifying articles therein; determining the location, dimensions and supposed
mass of an unidentified article; determining and forming a directional pattern of the
neutron radiator corresponding to the dimensions of the unidentified article. The method further includes subsequent thermal
neutron irradiation of the area with the unidentified article; recording gamma-ray quanta having the energy of 10.8 MeV and
cascade gamma-ray quanta with energies of 5.534 and 5.266 MeV by at least two gamma-ray detectors; counting of simultaneously recorded pairs of
cascade gamma-ray quanta; determination of the overall gamma-ray intensity, taking into account weight factors in readings of the detectors; determination of the threshold value for the overall gamma-ray intensity basing on the supposed
mass of explosive being detected; and making a decision in the event the threshold value of overall gamma-ray intensity is exceeded. When checking small-size objects, the
neutron irradiation step is preceded by replacing the
ambient air by a gaseous medium not containing
nitrogen.