Scientists use lasers to detect weapons-grade uranium from miles away

Nuclear reactor Kodak
The Cold War is decades behind us but nuclear arms are still an unfortunate reality. From afar, it isn’t always clear who is developing such weapons and intelligence has been known to be imprecise, leading to international finger-wagging at best and wars at worst.

But a team of researchers from the University of Michigan has turned to a technique used by the Mars rover to trace chemical weapons, using lasers to detect weapons-grade uranium at a distance.

“The primary obstacle to developing a nuclear weapons capability is getting hold of the right material,” Igor Jovanovic, professor and lead researcher, told Digital Trends. Of the two isotopes most commonly used in nuclear weapons, one — uranium-235 — is difficult to detect since it occasionally emits radiation.

“Our goal has been to find a way to detect this material,” Jovanovic said, “preferably at a distance, which is very difficult or even impossible using the available methods.”

The researchers were inspired after certain laser-based sensing methods — “specifically, laser-induced breakdown spectroscopy” — showed success, including by the Mars rover identifying material compositions on the red planet.

Jovanovic and his team turned to laser-induced breakdown spectroscopy and a phenomenon called laser filamentation, which enables them to measure from far away.

First, they fire laser pulses at an unknown material. The lasers interact with the material’s surface and produces a micro-plasma. This plasma interacts with oxygen in the air to produce excited oxide molecules that emit specific wavelengths of light, which can be detected and analyzed to infer what molecules, atoms, or isotopes are present.

The secret to the precise detection is in the isotopes. “The reason why we can make the measurements of isotopes more accurately is because we measure the light from molecules of uranium oxide,” Jovanovic explained. “It turns out that we can see a greater difference between different isotopes in uranium,” such as uranium-238 and uranium-235, “if we observe the emission from molecules rather than from atoms.”

In the past, laser filamentation can detect some materials from several miles away. For this to work, the uranium would need to be exposed in some way. For example, traces of uranium may be left in the dirt surrounding a manufacturing plant and the researchers would need to develop a more efficient system for light collection. Jovanovic suggested tools and tricks used by astronomers may help his team accomplish this.

First, the technique could be used for the obvious purpose of monitoring uranium production sites, ensuring that nations abide by nuclear treaties.

The second application could be in something called “nuclear forensics.” Jovanovic explained: “In nuclear forensics, the goal is to measure the properties of a measured material, such as uranium enrichment, accurately but also rapidly so that a proper attribution can be made and subsequent action taken. For example, in the case of a nuclear detonation, one would want to quickly measure the composition of explosion debris in a relatively inaccessible, high-radiation environment.”

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