According to new research published today in Scientific Reports, a team of nuclear engineers have used lasers to identify enriched uranium, a key ingredient in nuclear weapons, at a distance. This device could eventually be deployed in trucks or on drones to snoop out illegal nuclear activity and aid in non-proliferation efforts aimed at reducing the global nuclear arsenal.
Techniques for measuring chemicals at a distance are by no means new—it is one of the main techniques used by the Curiosity Mars Rover to sample the composition of the Red Planet's surface. Things get a little trickier when the technique is leveraged to measure isotopes (which describes to instances of the same element, only with different numbers of neutrons in their nuclei), but when it comes to measuring uranium at a distance, being able to parse isotopes makes all the difference.
Uranium is one of the more common elements in nature, with the World Nuclear Association reporting that it is "found in most rocks" in small quantities. The overwhelming majority (about 99.3 percent) of this naturally occurring uranium is uranium-238, an isotope that is incapable of sustaining the nuclear fission reactions needed for its use in nuclear weapons. But if you knock three neutrons out of the isotope's nucleus, you end up with uranium-235, the main ingredient in the world's most dangerous warheads.
When lasers are used to detect chemicals, the laser strikes the surface of the atom of the chemical and forms a plasma in the process. During this process, light is emitted at different colors that will then act as a fingerprint for that particular chemical.
As University of Michigan nuclear engineer Igor Jovanovic and his colleagues discovered, this also works to determine the difference between uranium isotopes, even when they're free-floating in the air. By firing very short and intense laser pulses at uranium isotopes, the researchers were able to turn both the uranium particles and the air around them into plasma. This allowed the uranium and the oxygen in the air to bond, and the energy levels stored in bonds between oxygen and uranium-235 or oxygen and uranium-238 are just different enough to be measured.
Read More: What is Uranium?
"These molecules radiate just slightly different colors, depending on whether we are looking at uranium-235 or uranium-238," Jovanovic said in a statement. "Not only is it possible to make measurements in air, but some constituents of air in fact make this detection more readily achievable."
Although the team was only able to test their device at a few meters distance in a laboratory at Penn State, they were testing it on weapons-grade nuclear material at the university's reactor. The results were reliable enough that the system could eventually be applied at distances upwards of a mile, so long as the uranium is exposed, as might be the case with the dust particles around a secret uranium enrichment facility, for instance.
Yet not all instances of this device's use need be applied to covert nuke facilities. The researchers also envision its use for things like nuclear forensics, which is used to determine the origin of nuclear material in the aftermath of an nuclear explosion, as well as monitoring the production of nuclear fuel at legit reactors to ensure the right levels of enrichment. According to Jovanovic's colleague Kyle Hartig, a nuclear engineer at the University of Florida, the technique may also find uses from further afield.
"This technique is not limited to uranium," Hartig said in a statement. "It is capable of simultaneous detection of molecules and atoms for the vast majority of elements in the periodic table."
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