Apparatus and method for detecting contraband using fast neutron activation

A method of detecting contraband in an object under investigation comprising:

• generating a collimated beam of fast neutrons;
• irradiating at least one section of said object with said collimated beam of fast neutrons, said fast neutrons interacting with atomic nuclei within said irradiated section to produce a gamma-ray spectrum having spectral lines characteristic of the elements contained within said at least one irradiated section;
• measuring the gamma-ray spectrum produced by said irradiation by detecting gamma-rays originating within said at least one section using a multiplicity of gamma-ray detectors judiciously positioned around said object;
• measuring the neutron flux that passes through said at least one section, said neutron flux comprising the number of neutrons that pass through said at least one section without interacting substantially with atomic nuclei;
• determining whether said measured gamma-ray spectrum and neutron flux indicate the combined presence of at least a plurality of elements from the group of elements consisting of hydrogen, carbon, nitrogen, and oxygen;
• and, if so
• identifying said at least one section as one that possibly contains contraband.

Apparatus for detecting a prescribed contraband material within an object under investigation comprising:

• means for generating high energy neutrons;
• means for irradiating said object with said high energy neutrons, said neutrons interacting with the nuclei of atoms of elements contained within said object, thereby causing gamma rays having a characteristic energy to be emitted, said characteristic energy uniquely identifying a particular element from which the gamma ray is emitted, the number of emitted gamma rays of a particular characteristic energy being a function of the spatial and density distributions of the corresponding particular element within said object;
• means for detecting the number of gamma rays emitted from the object at a plurality of prescribed characteristic energies, said means including a multiplicity of gamma-ray detectors judiciously positioned around said object;
• means for detecting the number of neutrons that pass through said object without interacting substantially with atomic nuclei of the elements within said object, the number of said passed-through neutrons providing an inverse measure of the density of atomic nuclei within said object;
• said gamma ray and neutron detection means thereby providing a measure of the spatial and density distributions of a corresponding plurality of elements within said object;
• and
• means for determining whether the measured spatial and density distributions of said plurality of elements corresponds to said prescribed contraband material;
• whereby the presence of said prescribed contraband material within said object can be detected.

Apparatus for non-invasively detecting contraband in an object under investigation comprising:

• means for generating fast neutrons;
• means for irradiating a prescribed portion of said object with said fast neutrons, the interactions of said fast neutrons with atomic nuclei within said irradiated portion of said object giving rise to a gamma-ray spectrum having spectral lines that comprise a unique signature of the nuclear species contained in said irradiated portion of said object;
• means for measuring the spectral lines of said gamma-ray spectrum to determine spatial and density distributions of the atomic nuclei of the elements that are contained within said irradiated portion of said object, said spectral line measuring means including a multiplicity of gamma-ray detectors selectively positioned relative to said object so as to sense gamma-rays emitted therefrom;
• neutron detection means positioned behind said object for detecting fast neutrons that pass through the irradiated portion of said object without interacting substantially with atomic nuclei therein, the number of fast neutrons that detected providing an additional measure of the spatial and density distribution of atomic nuclei within the irradiated portion of said object;
• and
• means for determining whether said spatial and density distributions of atomic nuclei correspond to contraband.