Next-gen separator harvests rare stable isotopes from heavier elements
To make the United States self-sufficient in rare exotic elements, the Oak Ridge National Laboratory (ORNL) has developed a latest generation electromagnetic isotope separator (EMIS) to harvest stable isotopes across the entire periodic table.
During the Second World War, the scientists working on what became the Manhattan Project to develop the world's first atomic bomb for the allies needed a way of separating the fissile isotope uranium-235 from non-fissile isotope uranium-238. With what were essentially unlimited resources except for time, they tried several different techniques, one of which was a derivation of the cyclotron called the California University cyclotron (calutron).
The calutron worked by inducing an electric charge in gaseous atoms and then accelerating them in an electric field. These speeding atoms are then deflected by a magnetic field. The clever bit is that the heavier the atom is, the less it is deflected. In the case of uranium, the U²³⁸ atoms U²³⁵ atoms deflect less than the U²³⁵ atoms, separating them out.
Though this method of producing fissile uranium was largely abandoned in favor of other methods after the war, the principle was developed by ORNL to produce stable isotopes. That is, pure samples of specific isotopes that are completely non-radioactive. These are used in a wide variety of applications, including water and soil management, environmental studies, nutrition assessment, and forensics.
However, ORNL shut down its Manhattan-era calutron in 1998, making the US dependent on foreign sources for these hard to produce isotopes to replenish dwindling domestic supplies. The first of these produced 500 milligrams of the rare isotope ruthenium-96 in 2018, which was unavailable anywhere in the world.
Today, the latest third-generation EMIS-3 units at Oak Ridge can outperform the old calutrons, which were a bit finicky. They had trouble resolving the difference between isotopes that were close together in mass and sometimes could only separate every other isotope in a sequence. This meant that isotopes had to be processed and reprocessed in batches to achieve the proper separation.
The new machines are much better at this and can handle elements at the heavier end of the periodic table, like ytterbium-176, which is used in nuclear medicine and radiology. Other ytterbium isotopes are used in quantum computing as well.
In addition, the EMIS-3 can separate different isotopes simultaneously because each EMIS unit can operate independently instead of needing to be hooked to one another in sequence to get the job done. They can also be reconfigured in weeks as opposed to gaseous centrifuge isotope separators (GCIS) that take years.
A new EMIS facility is under construction and is expected to be operational by 2030.
"The nice thing about EMIS-3 is that it’s a very solid platform for further development," said Brian Egle, head of Oak Ridge's Enrichment Science and Engineering Division’s Stable Isotope Research, Development and Production Section. “It’s extremely modular, and that gives the design a lot of flexibility. When you’re looking at the whole periodic table, flexibility is very important. If we need to add additional safety engineering controls for different toxicities or hazards, that’s easily done."
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