How can nuclear science help crime investigation?

Atoms do not lie. No matter how hard a criminal tries to hide, clean, or conceal evidence, there will always be some trace. Nuclear techniques make it possible to analyse samples collected from crime scenes (drug trafficking, murder, art forgery, etc.), such as glass fragments, bullet shells, human hair, fibres from artwork or soil, which, together with other forensic evidence collected by more traditional methods, such as DNA or fingerprints, can help find and prosecute perpetrators.

Common nuclear methods include X-ray techniques, neutron activation analysis, ion beam analytical techniques, and carbon-14 dating that analyse the chemical and physical properties of samples. Specialists can extract data that cannot be obtained by other techniques, e.g. the age of a forged work or the presence of poison in the victim's body.

These techniques have advantages over conventional methods in that they are much less destructive than other methods in that they analyse one particle in millions and determine its origin accurately, without altering essential tests as chemical analyses do, which can alter the original conditions of fragile samples.

X-ray techniques

Source: IAEA

It is well known that X-rays can be used to solve crimes such as, for example, a case in the late 1970s in the United States, where the prosecution compared bites on a victim's body with an X-ray of a suspect's jaw.

The use of radiation from X-rays is one of the most widely used analytical tools in forensic investigations because the techniques used are reliable and accurate, can be applied to tiny samples, most of the time the X-rays do not destroy them, and produce results within minutes so that several analyses can be performed in a short period of time. In addition, because some X-ray equipment can be easily transported, it is possible to use it directly at the crime scene.

X-ray techniques are used to detect the presence of certain chemical elements in almost all materials. X-rays can be used to analyse the composition of soil, drugs or minerals to deduce where they come from and to obtain data useful in comparative examinations of paints, metals or gunshot residues, as well as in medical examinations.

Scientists use devices such as X-fluorescence spectrometers or synchrotrons to irradiate material samples with X-ray beams that interact with atoms in the sample, releasing energy that can be measured. After analysing these measurements, scientists can conclude which types of atoms have released that energy within the sample.

Neutron Activation Analysis (NAA)

Source: OIEA

Researchers have been using neutron activation analysis for decades to calculate the concentrations of chemical elements, or their isotopes, in samples of evidentiary items such as bullets.

In AAN, experts study the interaction between the neutron flux and the analysed material to understand the isotopic composition of the analysed material, which allows them to draw conclusions about its age and provenance. To do this, the experts irradiate a sample with neutrons, whose atoms would react by releasing energy that can be measured and analysed with a special detector.

This technique is commonly used to determine the origin of bullets and to detect the presence of drugs or other toxic substances in the body by analysing hairs and to verify the origin of foods that are traded at a high price, such as some species of truffles from certain places, and to detect whether it is a food fraud or the real product.

Ion beam analysis

To do this, scientists use an accelerator to greatly increase the speed of ions or electrons to generate a beam of charged particles that come into contact with forensic samples, releasing energy that can be analysed.

Non-destructive analysis of ion beams in a work of art
Source: Jozef Stefan Institute (Slovenia)

With this technique, it is also possible to understand the chemical composition and thus the origin and age of drug substances, explosives, gunshot residue and works of art, among other things.

Through gunshot residue analysis, authorities can investigate violent crimes involving firearms and detect, for example, minute particles on a suspect's clothing or hands, which in turn can confirm the perpetrator of the crime.

Ion beams can also be used to analyse glass fragments from vehicles in car accidents or criminal investigations. Through a combination of ion beam analysis and artificial intelligence, it is possible to find out which car model has windows that correspond to the analysed glass fragments with a reliability of 80%.

Carbon 14 dating

Radiocarbon dating is a method in which an isotope, carbon-14, is used to calculate the exact age of ancient objects that include organic matter in their composition and to detect forged works of art.

This method has been used to date objects up to 50,000 years old and to resolve investigations into the authenticity of paintings, statues, and other valuable historical artifacts.

Discoverers of Carbon 14 (Samuel Ruben on the left and Martin Kamen on the right)

Other methods

Other nuclear techniques commonly used in forensic investigations include stable isotope analysis of foodstuffs. The latter allows experts to verify the origin and authenticity of different foods and to prosecute those responsible for adulterations, such as the sale of low-quality products labelled as premium products.

In this type of analysis, stable isotopes are measured with specialised equipment that detects small differences in the proportions of heavy and light forms of atoms of different chemical elements.

IAEA in the fight against crime

The International Atomic Energy Agency (IAEA) has an international network of national nuclear laboratories that provides concrete tools to forensic science experts and criminal authorities through the technical cooperation programme and coordinated research projects to obtain information on the origin and authenticity of foodstuffs, verify the authenticity of works of art and analyse evidence in criminal investigations.

The IAEA also provides technical assistance to countries to build their forensic capabilities, through training, scientific visits, and advice, and helps to strengthen relationships between the scientific community, authorities, and forensic experts seeking to prevent or prosecute criminal activities worldwide through the use of nuclear science and technology.

Collaborating agencies include the United Nations Office on Drugs and Crime (UNODC), the United Nations Interregional Crime and Justice Research Institute (UNICRI), the United Nations Industrial Development Organization (UNIDO), and the Food and Agriculture Organization of the United Nations (FAO), as well as other international partners.

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