Cleaning up and simplifying californium production

Radioactive californium-252 is a prolific neutron emitter, making it useful for examining jet engine parts for defects, finding underground oil and gas reservoirs, bombarding certain tumors, and operating nuclear reactors, among other things. Californium is also a superheavy element, a member of a small club whose chemistry still isn’t well understood. At the American Chemical Society national meeting in San Diego on Wednesday, researchers described a new way to produce the isotope that is more efficient than existing ones.

Seventy percent of the world’s ²⁵²Cf production happens at Oak Ridge National Laboratory, in radiation-shielded, remotely-operated labs called hot cells. The decades-old process starts with dissolving irradiated curium targets in concentrated nitric acid to isolate heavy elements through a cationic exchange process that separates ²⁵²Cf and other products chromatographically. This step involves materials that can’t tolerate high acidity, so chemists have to raise the solution’s pH significantly before proceeding. The pH balancing step is expensive because it produces waste and takes time to manipulate samples in the hot cells.

In a session organized by the Division of Nuclear Chemistry, ORNL radiochemist Lætitia H. Delmau described a revised ²⁵²Cf purification process that could reduce cost and waste. The method uses a neutral ligand, tetraoctyldiglycolamide, to extract ²⁵²Cf from the nitric acid solution, eliminating the need for a cationic exchange separation.

Delmau reported recovering 99% of ²⁵²Cf in small-scale tests of her method and was able to recycle the solvents she used. She also found the ligand preferentially bound actinide elements, like Cf, over other elements in the solution, improving separation efficiency.

Jenifer Shafer, a nuclear chemist at the Colorado School of Mines who organized the session, said Delmau’s efforts could make research on heavy elements like californium more accessible. She said the cost of purifying ²⁵²Cf and dealing with its waste is not trivial. “Everything we can do to improve cost factors and improve dissemination to other chemists” will help scientists discover more about this region of the periodic table, Shafer said.