Radioactive material can be seen when “no longer there” with new method
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Researchers from North Carolina State University have developed a technique to allow the characterisation of nuclear material in a location even after the material has been removed.
The approach is based on how radioactive material can change the arrangement of outer electrons in insulator materials such as brick, porcelain and glass.
By collecting samples of different materials in a room and evaluating the arrangement of electrons at defect sites in the crystalline structure of, for instance, brick walls, an investigator can determine whether there were any nuclear materials in that room and, if so, how potent they were.
“If the samples were taken at regular intervals in a grid pattern, the relative radiation dose profile can be used to triangulate where in the room the source was located, in three dimensions,” said Professor Robert Hayes, a nuclear engineer at North Carolina State University. “Basically, we can see nuclear material that is no longer there.”
Measuring the radiation dose at various depths of a sample of insulating material can also help inform an investigator about the type of radiation source that was present at the scene: gamma rays are likely to penetrate the entire thickness of the material, while beta radiation is less penetrative and alpha radiation the least penetrative.
This is not “extremely precise,” Professor Hayes admits, but it can help investigators answer important questions. For instance, it could help distinguish between naturally occurring nuclear material, medical materials and “special” nuclear materials used to create weapons.
This could be particularly significant in policing nuclear non-proliferation agreements and in security applications, and could, for instance, allow an investigator to identify and characterise a dirty bomb based on samples taken from a room the bomb was once stored in.
“This is a valuable tool for emergency responders, nuclear non-proliferation authorities and forensics, because it allows us to get a rough snapshot of the size of a radiation source, where it was located, how radioactive it is, and what type of radioactive material it is.”
“You can’t handle nuclear material in secret anymore,” he concludes. “It means the world is now densely blanketed by low-resolution integrating gamma-ray spectrometers, so we can always go back and measure what was present. There’s no hiding.”