Laser-produced uranium plasma evolves into more complex species

When energy is added to the uranium under pressure, a shock wave is created and even a tiny sample vaporizes like a small explosion. By using smaller controlled explosions, physicists can test on a microscopic scale and in a safe laboratory environment what one could only test previously in larger experiments and more dangerous with bombs.

"In our case, it is the laser that deposits energy in a target, but you get the same formation and the evolution of uranium plasma as a function of time," he said. the author Patrick Skrodzki. "With these small-scale explosions in the lab, we can understand a similar physics."

In a recent experiment, scientists working with Skrodzki used a laser to remove atomic uranium, stealing its electrons until they ionized and transformed into plasma, while recording chemical reactions in the form of more complex oxides formed, cooled by plasma. Their work places the uranium species and the reaction pathways that separate them on a map of space and time to determine the number of nanoseconds that they need to form and to which part of the evolution of the plasma.

In their article, published this week in Physics of plasmas, the authors discovered that uranium forms more complex molecules, such as uranium monoxide, uranium dioxide and other larger combinations, when it mixes with different percentages of oxygen.

"We used optical emission and examined excited states that were disintegrating in fundamental states, but this is only a small fraction of the image," Skrodzki said.

Uranium, with its 92 electrons and about 1,600 energy levels, can produce a complex spectrum that is difficult to decipher, even with high resolution spectroscopy. In the paper, the authors focused on an energy transition in plasma. They closely examined plasma plume morphology, collisional interactions with various oxygen concentrations, and other factors, such as plume containment and particle velocity, to provide a detailed picture of the plasma plume. the evolution of species, from atomic uranium to more complex uranium oxides.

The data obtained has implications for technologies that use lasers to probe materials and detail their elemental composition, such as the Mars Curiosity rover laser spectroscopy system. It can also be used with a portable device to check the compliance of a nuclear treaty by looking for evidence of enriched uranium production.

"There is still a lot of work to be done on this subject," Skrodzki said. "It's a scientific question because nobody knows anything about the optical emission in the visible region of these higher oxides. We want to try to provide data to fill those gaps."