Radioactivity and radiation against trafficking and crime
Editorial review 2026
Certain Customs checkpoints have heavy installations capable of radiographing an entire truck. These radiographs use gamma rays which are more penetrating than the X-rays used in conventional radiography. Customs officers have thus detected drugs hidden in a fake engine compartment and arrested the truck driver. Sophisticated reconstructions are needed to visualize the contents of the truck in space and perform cross-sections of suspicious areas.
Explosives detection
On the left, three gamma radiographs of a suitcase (A): at the top, on a conventional radiograph, the darker areas are the densest; in the middle, resonant radiography, where the darker areas correspond to a higher nitrogen density; at the bottom, the result of processing the two images reveals a block of Semtex explosive. (B) Radiographs on the right of a second suitcase. This time the explosive is concealed in the lid (false bottom). © DR
Nuclear techniques make it possible to improve the detection of explosives in airports. Baggage is subjected to radiography using gamma rays whose energy – 9.17 MeV (Nuclear Resonance Absorption – NRA) – corresponds exactly to the excitation energy of nitrogen nuclei, an element present in high concentration in explosives. These nuclei de-excite by re-emitting gamma rays. A double radiography is carried out: a standard radiography and a “resonant” radiography in which the amount of photons absorbed and re-emitted by the nitrogen contained in the inspected object is measured. Standard radiography is sensitive to dense materials, resonant radiography to nitrogen-containing products. Comparing the two images makes it possible to precisely locate suspicious substances.
Another application is that of portable explosive detectors. Used in countries devastated by war, these detectors could make it possible to clear minefields. These devices use neutrons because of their penetrating power. As they penetrate the ground, neutrons interact with the nuclei of nitrogen, carbon and hydrogen compounds making up common explosives. The nuclei that capture these neutrons de-excite by emitting characteristic-energy gamma rays. By detecting and measuring the energy of these gamma rays, it is possible to determine the chemical nature of the atoms present in the ground and deduce the presence of explosive substances. Portable neutron sources are required, for example Californium-252. This artificial nucleus located far beyond uranium undergoes 3% spontaneous fissions producing neutrons.
Weapon detection in a suitcase
The conventional radiograph of this briefcase provides little indication about the nature of the objects it contains. On the other hand, the same briefcase, radiographed using low-Z backscatter technology, reveals the outline of a pistol in its holster. © DR
Police and customs services use the techniques developed by nuclear physicists to combat drug trafficking, arms trafficking and terrorism. They use radiation sources other than radioactive sources, notably gamma rays produced using small accelerators, ultra-sensitive detectors and image reconstruction techniques developed in their experiments.
Low-density organic materials appear practically transparent in conventional X-ray or gamma radiographs. This is the case for organic materials used in explosives that are rich in carbon, oxygen, nitrogen and hydrogen atoms, light atoms whose atomic number Z is low.
American engineers working in the field of counterterrorism have succeeded in producing images highlighting these organic materials by means of an X-ray or gamma-ray beam scanning the object being examined. The intensity of the scattered rays is measured and recorded for the image according to the position of the beam. Backscattering (bouncing backward) is particularly intense when the rays interact with explosives, plastics or other organic materials rich in low-Z atoms. Even inorganic objects, made of metals, appear in these images with their shape and contours allowing them to be identified.