Common Bricks May Record Evidence of Nuclear Weapons

By Ryan F. Mandelbaum on at

Researchers have long studied retrospective dosimetry—looking at what kind of radiation was present in a room based on the signature left over in the environment. Frequently, this requires lots of treatment and work. One team of researchers at North Carolina State University thinks they have a simple way to detect the leftover radiation simply by taking a core of material out of a brick. Something like this could be important for things like nuclear weapons inspections.

“The potential is there for it to be something really important for the nonproliferation regime,” graduate student Ryan O’Mara told Gizmodo.

The system uses methods already used by archaeologists to date their finds, said O’Mara. Essentially, radiation such as gamma rays or x-rays can excite electrons in quartz crystals. The electrons get trapped in parts of the crystal’s structures and stay there for a while. Counting the electrons by exciting them out of the trap allows the researchers to see how much radiation there was in the room and where it came from.

Previous studies have treated the bricks first, but O’Mara and his adviser wondered if they’d be able to read the radiation without isolating the quartz grains. After testing some bricks with a radiation source, drilling a core into the brick, and reading what came out, they found that they could pretty faithfully reconstruct whatever was going on in the room. They published their paper in the most recent issue of Health Physics.

This is a difficult problem to solve. There are potential calibration issues, since building materials are all different, pointed out Stephanie Keehan, nuclear physics lecturer at RMIT University in Australia. She wasn’t sure that the method without treating the bricks first was valid and would like to see the experiment repeated. Melissa Spencer, health physicist at Penn State University, told Gizmodo in an email that she agreed in the calibration issues.

Spencer thought the technique could be important. “What is so interesting about this technique is not only that it could significantly reduce processing time and equipment needed (which is invaluable in an accident scenario), but also that it has the potential to identify what specific kind of radiation caused the dose, which helps to answer the question, ‘What happened here?’”

There’s plenty more work to be done, of course, and other ways to passively detect radiation, including “neutron activation analysis,” pointed out Keehan. In that analysis, elements in a material are identified by bombarding them with neutrons. But she noted that while not being so revolutionary, the method could make it easier to determine what kind of radiation the brick saw.

That’s end goal here, after all, said O’Mara: To make it more difficult for people to build nuclear weapons without getting caught. “If this method is deployed in the field, there’s always a detector watching.” [Health Physics]

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