Techniques, systems, and devices are disclosed for constructing a scattering and stopping relationship of cosmic-ray charged particles (including cosmic-ray electrons and/or cosmic-ray muons) over a range of low-atomic-mass materials, and to detect and identify content of a volume of interest (VOI) exposed to cosmic-ray charged particles based on the constructed scattering and stopping relationship. In one aspect, a process for constructing a scattering-stopping relationship for a range of low-density materials exposed to cosmic-ray charged particles is disclosed. This technique first determines a scattering parameter and a stopping parameter for each material within the range of low-density materials exposed to charged particles from cosmic ray. The technique then establishes a scattering-stopping relationship of cosmic ray charged particles for the range of low-density materials based on the determined pairs of scattering and stopping parameters associated with the range of low-density materials.

Technologies related to determining elemental composition of a sample that comprises fissile material are described herein. In a general embodiment, a pulsed neutron generator periodically emits bursts of neutrons, and is synchronized with an analyzer circuit. The bursts of neutrons are used to interrogate the sample, and the sample outputs gamma rays based upon the neutrons impacting the sample. A detector outputs pulses based upon the gamma rays impinging upon the material of the detector, and the analyzer circuit assigns the pulses to temporally-based bins based upon the analyzer circuit being synchronized with the pulsed neutron generator. A computing device outputs data that is indicative of elemental composition of the sample based upon the binned pulses.

A .sup.3Helium gas counter comprising a container, a gas tube within the container, and a mixture of .sup.3Helium and Xenon or a mixture of .sup.3Helium and Krypton. A method of making a .sup.3Helium gas counter comprising providing a container, placing a gas tube within the container, and depositing a mixture of .sup.3Helium and Xenon or a mixture of .sup.3Helium and Krypton into the gas tube.

A neutron detector system for discriminating fissile material from non-fissile material wherein a digital data acquisition unit collects data at high rate, and in real-time processes large volumes of data directly to count neutrons from the unknown source and detecting excess grouped neutrons to identify fission in the unknown source. The system includes a Poisson neutron generator for in-beam interrogation of a possible fissile neutron source and a DC power supply that exhibits electrical ripple on the order of less than one part per million. Certain voltage multiplier circuits, such as Cockroft-Walton voltage multipliers, are used to enhance the effective of series resistor-inductor circuits components to reduce the ripple associated with traditional AC rectified, high voltage DC power supplies.

A detector apparatus is provided and includes a collector having access to a sample of a gaseous fluid and a tester coupled to and disposed remotely from the collector. The tester includes a test chamber into which a sample is directed from the collector, an excitation element to excite the sample in the test chamber and a spectrum analyzing device coupled to the test chamber to analyze the excited sample for evidence of a concentration of particles of interest in the gaseous fluid exceeding a threshold concentration. The threshold concentration is defined in accordance with a type of the particles of interest and a residence time of the sample.

An apparatus comprises a neutron detector. The neutron detector comprises a conversion layer comprising a mixture of a neutron absorbing material and a scintillation material; and a photodetector optically coupled to the conversion layer and arranged to detect photons generated as a result of neutron absorption events in the conversion layer; wherein the apparatus is adapted to be carried by a user and the conversion layer is positioned within the neutron detector such that when the apparatus is being carried by a user in normal use neutrons are absorbed in the conversion layer after passing through the user such that the user's body provides a neutron moderating effect. In some cases the apparatus may be carried in association with a backpack or clothing worn by a user, for example, the neutron detector may be sized to fit in a pocket. In other cases the apparatus may be a hand-held device with the conversion layer arranged within a handle of the device to be gripped by a user when being carried.

Embodiments of the present invention disclose a nuclide identification method, a nuclide identification system, and a photoneutron emitter. The photoneutron emitter comprises: a pulsed electron accelerator configured for emitting electrons; and a photoneutron converting target configured to receive the electrons emitted by the pulsed electron accelerator and convert the electrons into photoneutrons. The photoneutron converting target has a volume of about 100 to about 8000 cm.sup.3, of about 100 to about 2500 cm.sup.3, or of about 785 cm.sup.3. These embodiments of the present invention can improve an accuracy of identification of a nuclide, and provide a practical photoneutron emitter, method and system for identifying a nuclide. Especially, these embodiments of the present invention can improve an accuracy of identification of a fissile nuclide such as .sup.233U, .sup.235U, and .sup.239Pu, and provide a practical photoneutron emitter, method and system for identifying a fissile nuclide such as .sup.233U, .sup.235U, and .sup.239Pu.

A scintillator stack includes a light-transportation layer and a scintillator layer. The scintillator stack can be included in a scintillator device. The scintillator stack can be made using a co-extrusion method.

An apparatus comprises a neutron detector. The neutron detector comprises a conversion layer comprising a mixture of a neutron absorbing material and a scintillation material; and a photodetector optically coupled to the conversion layer and arranged to detect photons generated as a result of neutron absorption events in the conversion layer; wherein the apparatus is adapted to be carried by a user and the conversion layer is positioned within the neutron detector such that when the apparatus is being carried by a user in normal use neutrons are absorbed in the conversion layer after passing through the user such that the user's body provides a neutron moderating effect. In some cases the apparatus may be carried in association with a backpack or clothing worn by a user, for example, the neutron detector may be sized to fit in a pocket. In other cases the apparatus may be a hand-held device with the conversion layer arranged within a handle of the device to be gripped by a user when being carried.

A human body back-scattering inspection method and system are discloses. The method includes: obtaining a back-scattering scan image of a human body under inspection; distinguishing a body image from a background image in the back-scattering scan image; and calculating a feature parameter of the background image to determine whether radioactive substance is carried with the human body. With some embodiments of the present disclosure, it is possible to determine whether any radioactive substance is carried with a human body during back-scattering inspection of the human body. In further embodiments of the present disclosure, it is possible to approximately determine which part(s) of the human body carries the radioactive substance. This improves efficiency of inspection.