Forensic nuclear techniques for crime investigation

La ciencia forense nuclear

Nuclear forensic science focuses on examining nuclear or radioactive materials that are outside regulatory control, to determine their origin, age, and possible connections to relevant individuals, locations, or events. Its purpose is to support investigations of crimes, terrorism, illicit trafficking, or nuclear proliferation.

The International Atomic Energy Agency (IAEA) provides technical assistance, training, coordinated research projects, and consultations to strengthen national capabilities in this field.

Practical applications in criminal investigation

Some practical applications of nuclear forensic science include:

• Identification of suspicious substances in drug trafficking, determining chemical traces and their geographical origin.
• Determining the age of forged artworks through C-14 dating or isotopic composition analysis.
• Analysis of poisons (for example, heavy metals) using advanced, light, and non-destructive techniques, complementing traditional toxicological tests.
• Comparison of residues in bullet casings or bullets through the analysis of invisible metallic components and particle microscopy.

The main techniques used

• Neutron Activation Analysis

One of the pillars of nuclear forensic science. It consists of irradiating the sample with neutrons in a reactor and analyzing the radiation emitted by the activated elements. It is extremely sensitive—capable of detecting quantities as small as micro-micrograms—and allows quantitative analysis without destroying the sample.

• X-ray spectroscopy and ion beam techniques

These techniques include methods such as X-ray fluorescence, absorption spectroscopy, and ion beam techniques to characterize the elemental composition and structure of samples. They have the advantage of being fast, in many cases portable, and non-destructive.

• Radiocarbon (C-14) dating 

Allows estimation of the age of organic samples or materials containing carbon, such as old paintings or textile fibers, which is key in detecting forgeries or altered evidence.

• Gamma-ray spectroscopy and alpha/beta counting

Measuring radioactive emissions (for example, using alpha particle detectors or gamma counting) makes it possible to identify specific radionuclides and estimate their concentration, providing information about the processing or origin of the material.

• Mass spectrometry: TIMS and MC-ICP-MS

Mass spectrometry can achieve extremely high isotopic resolution. There are two main techniques:

• Thermal ionization mass spectrometry (TIMS)
• Multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS)

Both techniques allow the distinction of nearly identical isotopes (e.g., ^235U versus ^236U), which is key for tracing sources and industrial processes. Their application requires a system to ionize the sample, a vacuum chamber, an analyzer to separate it, and detectors to measure it.

• Scanning electron microscopy (SEM) and spectroscopic imaging

This method makes it possible to analyze morphology and composition at the nanometric level, revealing processing or manufacturing marks on bullets, glass, or other materials. It is performed with a scanning electron microscope. Scanning electron microscopy reveals nanometric-level morphology and composition, showing processing or manufacturing marks on bullets, glass, or other materials.

•  X-ray absorption spectroscopy (XANES/EXAFS)

This technique is used to characterize oxidation states and atomic environments in uranium samples or other compounds. It is especially valued in complex cases. Spectroscopic imaging is performed with an X-ray detector coupled to the microscope.

• XANES (X-ray Absorption Near Edge Structure)
  Focuses on the region near the absorption edge.
  Provides information on oxidation state and chemical coordination.
• EXAFS (Extended X-ray Absorption Fine Structure)
  Analyzes the farther region of the absorption spectrum.
  Offers data on interatomic distances, the number of neighboring atoms, and the structural order or disorder around the atom.

Both XANES and EXAFS techniques require a synchrotron, a monochromator, a sample holder, and X-ray detectors.

• Objective color analysis

Through quantified digital images taken with high-resolution digital cameras, the color of compounds such as uranium peroxides is studied to infer thermal treatments or processes applied. Each pixel is represented by numerical values in a color model, allowing the images to be analyzed, processed, or compared in a more mathematical and precise way.

There are two color models for these images:

• RGB (Red, Green, Blue): Based on the combination of the three primary colors of light. It is used in screens, cameras, and most digital devices.
• HSV (Hue, Saturation, Value): An alternative model that describes color in a way that is more intuitive to the human eye:
  • Hue = the type of color (red, green, blue, etc.)
  • Saturation = the intensity or purity of the color
  • Value = the value or brightness (how light or dark the color is)

Requirements of nuclear forensic techniques

Nuclear forensic techniques require specialized infrastructure, such as nuclear reactors, high-resolution mass spectrometers, or ion beams. It is also necessary to maintain a strict chain of custody, implement protocols that prioritize non-destructive methods, and foster cooperation between international forensic laboratories. Nuclear forensic capability is not limited to having advanced equipment: it requires training and interdisciplinary expertise spanning nuclear science, criminalistics, and nuclear security.

The Joint Research Centre of the European Commission and the IAEA work together to advance nuclear forensic science through coordinated projects and specialized training.

Real cases where nuclear techniques were applied to criminal investigation

Contaminated letters in Romania (illegal use of isotope I-125)

In an unusual case, a group of criminals used letters contaminated with iodine-125—normally used in medical treatment—to impersonate an opponent in gambling and gain a financial advantage. Although the carriers were unaware of the radiation, nuclear monitoring and analysis detected the isotope. Nuclear forensic techniques identified the presence of the radioactive material and its origin, and the results were essential for prosecutors to establish intent and link the criminal group to the events.

The investigation received support from the IAEA and the International Nuclear Forensics Research Network, and the nuclear analysis was integrated into the expert evidence used in court.

Assassination of Alexander Litvinenko (Polonium-210, 2006)

Alexander Litvinenko was poisoned in London with polonium-210, an extremely radioactive isotope. The British authorities used a combination of analytical techniques to trace the source of the polonium and estimate the dose received. Although most information comes from government investigations, the case demonstrated how nuclear techniques can attribute responsibility in sophisticated assassinations involving radioactive substances.

International cooperation and databases such as the IAEA's Incident and Trafficking Database (ITDB) have been essential for sharing standards, comparative references, and best practices.

 

Sources: IAEA, European Commission, ScienceDirect