Nuclear detectionHow Lasers Can Help with Nuclear Nonproliferation Monitoring

Published 17 April 2020

Scientists developed a new method showing that measuring the light produced in plasmas made from a laser can be used to understand uranium oxidation in nuclear fireballs. This capability gives never-before-seen insight into uranium gas-phase oxidation during nuclear explosions. These insights further progress toward a reliable, non-contact method for remote detection of uranium elements and isotopes, with implications for nonproliferation safeguards, explosion monitoring and treaty verification.

Mountains. Shipping containers. The surface of Mars.

There are times when it’s complicated or impossible to bring a sample into a laboratory to test its composition.

This is especially true when it comes to detecting explosions containing nuclear material. Detection that can be done quickly or onsite minimizes human exposure during hazardous collections or laboratory analysis.

However, the nature of nuclear chemistry—particularly oxidation, the way uranium interacts with oxygen during a nuclear explosion—is largely unknown, leaving gaps in our ability to accurately identify nuclear activities. A team of researchers led by PNNL physicist Sivanandan S. Harilal is working to expand our uranium chemistry understanding using a surprising tool: lasers.

PNNL says that the method, detailed in a recent paper in the Journal of Analytical Atomic Spectrometry, shows how measuring the light produced in plasmas made from a laser can be used to understand uranium oxidation in nuclear fireballs.  This capability gives never-before-seen insight into uranium gas-phase oxidation during nuclear explosions. These insights further progress toward a reliable, non-contact method for remote detection of uranium elements and isotopes, with implications for nonproliferation safeguards, explosion monitoring and treaty verification.

Nonproliferation Plasmas
A pulsing, fast-as lightening laser blasts into a solid material and excites the atoms so they vaporize into a tiny, brightly colored plume of plasma. The reaction when the atoms jump into this superhot plasma plume emits light which researchers can capture and study using optical spectroscopy.

Plasmas made from different elements at different temperatures emit different wavelengths of light, each of which produce a distinct color. Thus, the color of plasma in a candle’s flame is different than the plasma made in a neon sign, or the microscopic plasma plume Harilal and his team generate to study uranium.

The distinct colors of light emitted by a plasma are the same no matter how much of a material is turned into a plasma. Harilal’s uranium laser produced plasma (LPP) is made from such a small amount of nuclear material that the method can be considered non-destructive. Even so, the light measurements researchers get from LPP is similar to the reactions in the fireball produced during a nuclear explosion.

“It’s a question of scale,” says Harilal. “The lasers create the same fireball chemistry that happens in a nuclear explosion, so we can study the chemistry and how it reacts to different environmental conditions. It’s small, but the light is good. We can collect it with no problem.”