Chemists introduce novel method to separate isotopes

October 24, 2017 by Louise Lerner, University of Chicago
In a new method to separate isotopes, atoms directed at a specially crafted atomic lattice bounce off at different angles based on their different quantum wavelengths. (The red track represents a lighter isotope, the blue track a heavier one.) Credit: Arin R. Greenwood, Federico Giberti, and Kevin J. Nihill

Separating different versions of elements—isotopes—is an excruciatingly difficult task: They differ by just one or two extra neutrons, an infinitesimal difference in mass. But University of Chicago researchers announced Oct. 23 that they've added an entirely new way to do so.

In a paper published in Physical Review Letters, a team led by Prof. Steven J. Sibener describes a way to separate isotopes of neon using a beam of gas aimed at a precisely patterned silicon wafer, which reflects the different isotopes at slightly different angles. The method could one day be a less costly and more energy-efficient way to separate isotopes for medicine, electronics and other applications.

The few neutrons' difference in an isotope can make a world of difference to its usefulness. Today, the most common isotopes of interest are uranium for nuclear energy and a constellation of radioisotopes for medical treatments, but enrichment is also increasingly of interest in the electronics world. In particular, isotopically pure silicon makes much more efficient transistors for chips, and holds significant promise for quantum computing.

But the difficulty in the task—current commercial methods generally involve lasers or bombarding an element with electrons until it ionizes, and often multiple repeated rounds to get the numbers higher—has limited its common use.

Sibener's team instead started with a supersonic beam of neon, in which all atoms have been accelerated to the same high speed. The beam slams into a crystalline surface whose atoms are arranged in just the right lattice formation so that incoming atoms are flung off at slightly different angles depending on their isotopic composition.

"One can think about it like separating the various colors of light into a rainbow using a prism," said Sibener, the Carl William Eisendrath Distinguished Service Professor of Chemistry and the James Franck Institute.

The method could be used for lighter elements on the periodic table, up to about atomic mass 40, as well as small molecules, said graduate student Kevin Nihill and postdoctoral scholar Jacob Graham, co-first authors on the paper.

They also noted that the bounce off the surface at slightly different velocities, which suggests the method could be augmented to yield higher levels of enrichment and purification using velocity separation.

"This is a wonderful and very precise demonstration study, and we are very pleased with the results," Sibener said. "It has been a delight to run down to the lab every day to see what's happened. We're very much looking forward to planning the next steps in this project to explore other atoms and molecules."

Explore further: Researchers develop technique that could detect explosives, dangerous gases rapidly and remotely

More information: Kevin J. Nihill et al. Separation of Isotopes in Space and Time by Gas-Surface Atomic Diffraction, Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.119.176001

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4 comments

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RogueParticle
1 / 5 (2) Oct 24, 2017
They differ by just one or two extra neutrons, an infinitesimal difference in mass.
For naturally occurring uranium, the two isotopes of interest are U235 and U238, the nuclei of which contain (surprise!) 235 and 238 nucleons. The difference in mass between them is (roughly) 235/238 = 1.26%, which could hardly be described as infinitesimal.
rrwillsj
1 / 5 (3) Oct 24, 2017
RP, your facts are correct. However, I think the writers of this article were generalizing about a novel method of processing all the elements.

Speculating at possible, even though improbable, discoveries. When simpler, cheaper methods of separating isotopes are developed.
Steelwolf
not rated yet Nov 08, 2017
RP, when considering the difference betwen the basic isotopes of hydrogen, Hydrogen, Deuterium and Tritium, one or two neutrons IS a HUGE difference, but that is not the thrust of the article. Going from Tritium to Helium turns a once nicely fusible isotope into a neutron scavenger, which can kill yer reaction doublings real quick, half a shake or so.
So come down off your condescending high horse and quit acting like a science Trump.
Steelwolf
not rated yet Nov 08, 2017
Being able to accurately define, create and then filter out specific isotopes is a very huge thing, This will actualy help to answer a lot of questions some of us differ on in our theories. More difinitive answers is a good thing.

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