If walls could talk, would they tell you the whereabouts of secret, weapons-grade plutonium? According to a team of nuclear engineers, yes.
In a study published this month in the journal Radiation Measurements, a team of nuclear engineers have shown how everyday building materials like brick and title can be used to look back in time at a environments' nuclear history and paint a 3D picture of what kind of materials may have been there and how strong their radiation was. This research can help nuclear inspectors tell the difference between a building used to make nuclear power and one used for more nefarious purposes.
Robert Hayes, the study's first author and associate professor of nuclear engineering at North Carolina State University, tells Inverse that using these building materials as "gamma-ray cameras" allows them to look retroactively at these materials even if they've since been removed from the environment.
"This method does it retrospectively," Hayes tells Inverse. "The way it is [typically] done now is I would actually have a radiation detector in my hand that requires electricity or battery power and that only measures the [radiation source] when it's there. So if I take the source away, my detector is not going to see anything."
Instead, Hayes' team has developed a way to rewind the footage that insulators in the environment, like light fixtures or bricks, would have captured about the nuclear material just by being near it. Radiation will leave a mark on these materials similar to how the smell of a bonfire will stick to your clothes for days. In this way, the researchers can see back in time to where and when the source of radiation was.
"A brick is really just mud."
"What we've developed is a way to say 'Well, the source was there in the past' and the detector was there because [the material] was in the vicinity of various [insulating] materials."
The team's latest study focused on how this can be achieved using commercial grade dosimeters, device sdesigned to sense ionizing radiation, but Hayes tells Inverse that they have already proven that this works just as well in material like bricks too, thanks to radiation-absorbing silicate in the material.
"A brick is really just mud," Hayes tells Inverse, "[but] when you remove silicates from that sintered mud... those silicates become dosimeters."
Using these techniques, Hayes tells Inverse they can determine what kind of nuclear source existed in the environment before they arrived, where in the environment it was and even how long it'd been there. But, that last part can be tricky, says Hayes, and depends on the material's half-life.
"The signals that you measure from the bricks have a certain half-life," Hayes tells Inverse, referring to the amount of time required for the radioactivity of an object to decrease by half. "If I was to use calcified tissues like a shark's tooth or deer's antlers, the half-life in those calcified tissues tends to be on the order of millions of years."
Materials like quartz found in bricks and tiles have half-lives of similar lengths, but softer materials like linen have much shorter half-lives and thus cannot see into the past quite so well.
"It's like Harry Potter magic."
Going forward, Hayes says they hope to next refine the sensitivity of this technique so that's it's able to better differentiate between low dose and high dose sources as well as be more sensitive to materials with lesser half-lives, like shirt buttons or plastic.
"This is crazy cool science," Hayes tells Inverse. "It's like Harry Potter magic what we can do now that we could not do before."
Abstract: A 4.5 kg sphere of α-phase plutonium was subjected to passive imaging using optically stimulated luminescence dosimetry techniques via inverse square modeling under cylindrical symmetry around the dosimeter array. The results showed angular resolution in the localization capability close to 1° due to axial resolution below 1 cm. Radial resolution was much worse having an offset of 16 cm using only point source geometry estimates for the commercial dosimeters. Using MCNP™ to reconstruct the profile demonstrated a substantial improvement in reconstructing the relative response as opposed to assuming simple point source geometry. From this, an inverse solving approach known as DRAM was used to estimate source distribution in addition to location. These results are considered regarding their implications for nuclear nonproliferation to the extent they demonstrate potential to determine whether illicit nuclear material had historically been kept in any specific location or alternatively, whether such materials had not been kept in a location they were claimed to have been stored. Having measured the materials location and knowing the integrated measurement time then allows estimating amount of material via dose (or alternatively, knowing the assay could give storage time estimates).