An inventive solution speeds up production of actinium-225

August 5, 2021, 12:00PMNuclear News
Chemist Kevin Gaddis has adapted components of a high-pressure ion chromatography system to withstand the extreme conditions of a hot cell. (Photo: ORNL/Carlos Jones)

An Oak Ridge National Laboratory researcher has built a device that can speed up the separation of the medical radioisotope actinium-225 from irradiated thorium targets and withstand the high-radiation environment of a hot cell. In July, ORNL announced that Kevin Gaddis, a chemistry technician at the lab, had built and tested a prototype and was working to secure a patent for a device that cut separations time by 75 percent.

Defining the problem: According to ORNL, high pressure ion chromatography (HPIC), which uses a high-pressure pump to enable more rapid separation of ions, is one of the fastest and most efficient ways to do chemical separations. But thorium targets that have been irradiated in a particle accelerator must be handled in a hot cell, and high irradiation levels can destroy an HPIC’s electronic components.

Because high radiation can destroy the components, technicians have relied on gravity to perform separations in hot cells. But allowing solutions to drip through a column, rather than pushing them through, makes for a slower process.

Speed is important because demand is high for Ac-225, which has a half-life of 10 days. “Hours matter,” Gaddis said in an August 2 media statement from ORNL. “If we can reduce the time for the separation, we can get more product out.”

Finding a solution: Gaddis, who works with other ORNL scientists on a Tri-Lab Ac-225 production project with scientists from Los Alamos National Laboratory and Brookhaven National Laboratory, used radiation-tolerant materials to build a HPIC that uses air pressure rather than electricity to control the flow of the sample and chemicals that separate Ac-225 from byproducts. Gaddis designed the system so that the computer and electronic pump could be located outside the hot cell, according to ORNL. A simplified control panel, with air-actuated valves, controls the flow of liquid and chemicals.

The use of a hot cell with automated manipulator arms demanded other accommodations, including adequate space between separator columns, easy-to-flip valve switches, and 3D-printed threaded caps that could be sealed by the manipulators.

Testing in a mock-up of a hot cell using cold water showed that the system could perform the fourth separation step in the multi-step Ac-225 purification process—removal of adjacent lanthanides—in 75 percent less time than using the gravity-fed system. Gaddis aims to have the automated HPIC system installed in the hot cell used for Ac-225 production by the fall and hopes to use the system for more isotope separations, according to ORNL.

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