By Carolyn Krause/Special to The Oak Ridger
Posted Mar 12, 2019 at 5:06 PM
Oak Ridge National Laboratory will once again be producing an array of nearly pure, stable, nonradioactive isotopes with uses ranging from treating cancer and medical imaging to keeping airports safe.
Oak Ridge National Laboratory will once again be producing an array of nearly pure, stable, nonradioactive isotopes with uses ranging from treating cancer and medical imaging to keeping airports safe.
Brian Egle told Friends of ORNL last week that ORNL is reestablishing production of enriched stable isotopes for various applications as a result of a new program funded by the Office of Nuclear Physics in the Department of Energy’s Office of Science.
The new Enriched Stable Isotope Production Facility on the main ORNL campus combines an innovative method of electromagnetic isotope separation (EMIS) developed at ORNL in the past eight years with conventional gas centrifuge technology.
The aim of the program — carried out by Egle, Adam Stevenson, Clint Ausmus and Kevin Hart — is to produce efficiently and reliably kilogram quantities of target materials enriched in stable isotopes. Many of these target materials go to ORNL’s High Flux Isotope Reactor, where they are irradiated with neutrons and turned into radioisotopes.
The first product of the new program was a tiny vial of gray powder containing the rare isotope, ruthenium-96, which was not available anywhere in the world. The 500 milligrams of Ru-96 was used last year in a new experiment at the Relativistic Heavy Ion Collider at DOE’s Brookhaven National Laboratory. The experimenters needed it to detect and measure the intense magnetic fields created in nuclear collisions to better understand a form of matter present at the beginning of the universe.
“With gas centrifuge technology, we get high throughput but low enrichment for each stage,” Egle explained. “In our new electromagnetic isotope separator, we get low throughput —milligrams per hour — but high enrichment. To produce some stable isotopes in kilogram quantities, we need a large number of devices to reach significant enrichment.”
The original stable isotope enrichment program run by ORNL at the Y-12 National Security Complex started in the 1950s and ended in 1998, largely because of competition from Russia. The program used the Beta-3 calutrons for electromagnetic separation of isotopes. From 1943 to 1945, calutrons in nine buildings at Y-12 separated the least abundant isotope of uranium (U-235) from the most abundant one (U-238) to make a product enriched in fissionable U-235 for use in the first atomic bomb.
According to Egle, 90 naturally occurring elements on Earth are made up of 266 stable isotopes. Isotopes of the same element are chemically the same but have a different number of neutrons in their atomic nuclei. Enriched isotopes are used in medical imaging and treatments, basic scientific research, industry, nuclear energy and national security.
“We have $360 million worth of stable isotope inventory,” Egle said. “We do a wide range of metallurgical, ceramic and vacuum processing of custom materials.”
He showed a slide of a penny-size disk of nearly pure copper-65 enriched by Scott Aaron, retired program director. This coin is worth $180,000. Despite the cost of materials enriched in stable isotopes, the demand is rising. Customers send in inquiries and order isotopes through the www.isotopes.gov website of DOE’s revived isotope distribution program.
At many U.S. airports, passengers’ hands, shoes and bags are swabbed to check for the presence of nitrogen, an ingredient of explosives. Nickel-63, a radioisotope made at HFIR from a target enriched in stable nickel-62 at ORNL, is used for detection of an unusual concentration of nitrogen, which usually indicates the presence of explosives at airports.
ORNL researchers are working on preparing gas centrifuges to produce xenon-129 for medical imaging of human lungs to determine if chronic obstructive pulmonary disease is present. COPD causes increasing breathlessness in patients.
An ORNL priority for EMIS research is the production of lutetium-177, which was recently approved by the FDA for use in treatment of certain types of pancreatic cancer. If placed on sugar molecules, the gamma-ray-emitting isotope seeks out a tumor on the pancreas and destroys only the tumor tissue, not the healthy tissue.
One way to make lutetium-177 is to irradiate enriched ytterbium-176 in a reactor. The problem is that the only source of ytterbium is Russia, and the Russians will not sell this element to the Americans. However, ORNL plans to use EMIS to make targets enriched in lutetium-176 that can be irradiated with neutrons in HFIR to produce lutetium-177.
Burnable poisons are used in commercial nuclear power plants to produce a more level distribution of power in the reactor core and reduce the need for a large control system. An ideal burnable poison would also increase the fuel lifetime.
The neutron-absorbing gadolinium-157 isotope was found to have the right properties and, if pure, could save approximately $6 million at the end of four years of a commercial reactor’s operation. However, the cost of separation is too high now. ORNL researchers hope to show that plasma separation in a field of radio waves of a specific frequency can cost effectively produce gadolinium-157 in large quantities for the nuclear industry.
ORNL used calutrons to separate an element’s heavier and lighter isotopes and enrich a target material in one of the isotopes. The electrically charged atoms of the lighter isotope introduced into the magnetic field move in an ion beam in a tighter circle than injected ions of the heavier isotope, allowing separation and collection in a correctly placed pocket.
In the EMIS system, vacuum pumps have been replaced with a less expensive turbopump, and the researchers solved a problem to enable the production of higher-purity (99+ percent) isotopes that are caught in and removed from graphite pockets. In addition, the ORNL group replaced the calutron’s electron-emitting tungsten or tantalum filament in the ion source with a radiofrequency-driven electron gun containing argon.
“If you are trying to do EMIS 24/7 for 18 months and if you have to stop every 10 to 120 hours for four hours to replace a filament, your productivity will take a big hit,” Egle said. “With our rf-driven electron gun, we ran 24/7 for 50 days straight with no major interruptions.”
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