Radioactive substances leave electron ‘fingerprints’ behind

New forensics technique could help solve nuclear whodunits

Walls can’t talk, but scientists can now read stories written in their subatomic particles. And that could make it harder to store radioactive material in secret.

Nuclear radiation rearranges the electrons in insulators such as brick, glass and porcelain. So comparing the positions of electrons in atoms at different spots on walls, windows and floors could provide a rough snapshot of where radioactive material was once stored and how strong it was, researchers report online July 3 in Health Physics.

This technique could also help identify the source of radioactivity — which is important for judging whether a room contained legal radioactive material with a scientific or medical purpose or if it housed a substance used for making nuclear weapons.

That’s because different nuclear materials give off their own specific blend of gamma rays, X-rays and so on, and each type of radiation penetrates insulators with different strengths. So the variation in the distribution of electrons at different depths of an insulator reveals what kind of radiation it was exposed to, explains coauthor Robert Hayes, a nuclear engineer at North Carolina State University in Raleigh.

Hayes, along with Sergey Sholom of Oklahoma State University in Stillwater, tested this idea with two AAA battery‒sized capsules of radioactive substances — cobalt-60 and cesium-137. They set the capsules on top of two typical bricks, letting the substances saturate the bricks with radiation overnight. The scientists then removed chunks of brick from under each vial and examined the electrons at different depths. The electron patterns they observed were precisely what researchers expected to see from these two radioisotopes, Hayes says.

Authorities could use this technique to retrace where a dirty bomb was stored before detonation to figure out who built it, says Eric Lukosi, a nuclear engineer at the University of Tennessee, Knoxville who was not involved in the work.

“This is still very early in its development,” Lukosi says, “but it’s an interesting approach.”