Reduction of radiolysis in liquid targets for radiometal production: What not to do

Reduction of radiolysis in liquid targets for radiometal production: What not to do

Nicholas Zacchia, Mark Martinez, Stefan Zeisler, Cornelia Hoehr
TRIUMF, University of British Columbia Department of Chemical and Biological Engineering

Poster

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Research in PET imaging is starting to turn towards radiometal isotopes which provide a range of half-lives, binding affinities, and the potential for dual modality imaging and therapy. However, convenient access to these isotopes is lacking, hampering research efforts. One production route for radiometals is a solution target on a medical cyclotron. At TRIUMF, research quantities of 68Ga, 44Sc, 86Y and 89Zr are produced in a liquid target by irradiating nitrate salt solutions. A key drawback is that nitrate solutions increase gas production through radiolysis. This has meant steadily increasing target pressure during irradiations which either limits the amount of time we can irradiate, the beam current used or both.
Motivated to reduce pressure buildup inside of our target, we have explored the addition of catalytic particles to the irradiated solutions. The hope was that radiolytic H2 and O2 gas could be recombined to water. Nano to micro sized particles of platinum, palladium and rhodium were added to solutions of yttrium nitrate in 0.8 M nitric acid. Rather than reduce radiolysis, the addition of catalytic particles mostly increased pressure rise in the target as well as introducing undesirable effects in the transfer lines and valves.