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Explosives detection

Problem of the explosives detection

Among a lot of potential methods of terrorism (biological, chemical, radiation, explosives) problem of the explosives detection is a priority task due to the following reasons:

  • Explosives are most frequently utilized in terrorist attacks;
  • Explosives can be relatively easy be acquired or prepared from the available reagents;
  • Explosives can be easy transported and delivered into the target point;
  • Explosives are relatively hard to detect;
  • Explosives are comparatively easy to deploy.

Functional components of the bomb – controlling system, detonator, fuse and charge. A bomb can be identified by their form through x-ray screening. Although plastics and liquids explosive do not possess any particular forms and can be discriminated just by their chemical content.

Active Interrogation Analysis techniques are utilized for nondestructive identification of dangerous materials content. It is recognized today that most promising and mature technologies of explosive detection among list of other available options are Neutron Activation Analysis with its several modifications.

Ratec company developed and implemented in Explosives Detection Systems the neutron technologies based on well known analytical methods and their modifications:

Thermal Neutron Activation Analysis

Explosives in general contain more than 18% of nitrogen and that chemical property is utilized for their detection. Reaction of thermal neutron capture in nitrogen is applied for its concentration measurement and following identification of explosives: 
14N + nth → 14N(nth,ɣ) 15N

During interaction with neutron nitrogen gives off the unique characteristics gamma ray during the thermal neutron capture reaction (n,ɣ). Characteristics gamma rays are high in energy and can be detected by the detectors array. The information from the detectors goes to the computer and processes by special algorithms which look for certain signature patterns and making decision about explosive presence.

Thermal Neutron Analysis technique detects explosives based on elemental composition of the inspected object.

Pulsed Fast Thermal Neutron Analysis

Pulsed Fast Thermal Neutron Analysis utilized microsecond wide fast neutron pulses produced by electronic neutron generator. It measures carbon and oxygen content (evidence of explosive) during the pulses via detecting prompt g-rays resulting from fast neutron inelastic scattering reactions. In between the pulses neutrons are thermalized by low atomic mass elements in object content. Then nitrogen is can be detected via thermal neutron capture reaction (n,ɣ).

Pulsed fast neutron analysis

Pulsed mode of neutron irradiation allow the use of Time Of Light (TOF) technique which is useful for reducing the influence of background radiation from neutron interactions and can be used to determine the location of the detected material. 

It is possible when very short nanosecond fast neutron pulses can be produced. Then measurements of start time when neutron pulse is created and stop time when the  g-rays are recorded give information about object location and provide a possibility to ignore gamma ray from background in object content determination.

Associated Particles Imaging

Associated Particles Imaging technique is “Tagging” the primary neutron by associated alpha particles that are produced through deuterium-tritium (DT) fusion reaction in electronic neutron generator. That method can utilize Time of Light technique by measuring time of alpha particles detection and accepting for material content identification only those gamma-rays that coincide with “tagged” neutrons.