Uranium is actually a rather common element on Earth. You can find it in small quantities within most rocks, but 99.3% of that uranium is the relatively harmless uranium-238. It’s the much more rare uranium-235 that sustains nuclear reactions and is vital in the production of nuclear weapons. Naturally, being able to detect this isotope of uranium is important, and scientists from the University of Michigan think they’ve found a way to do that at a distance using lasers.
The physical difference between uranium-238 and 235 is miniscule — uranium-238 has three more neutrons than 235 does. That has a significant impact on its properties, making it useful in nuclear power plants and in nuclear weapons. In order to do that you need to enrich uranium it by concentrating the 235 isotope. Facilities that do this are highly regulated, and a “rogue” enrichment operation is bad news for everyone. That’s something authorities want to track down, but how?
A concentration of uranium-235 higher than the trace background levels indicates an enrichment operation. Scientists can differentiate these two isotopes from each other using a variety of methods. Although, most of them require close proximity to the sample. The laser-based system developed by U of M nuclear engineer Igor Jovanovic and his colleagues does not suffer that limitation.
The team used very short, high energy laser pulses to identify uranium isotopes. Plasma is momentarily formed when a laser of this sort (known as a femtosecond filament laser) strikes an object, which in this case leads the uranium atoms to form a bond with oxygen in the atmosphere around them. By analyzing the optical and acoustic spectrum of the resulting uranium oxide molecules, the researchers confirmed there’s a measurable difference between natural and enriched uranium.