Resonant laser ionization and mass separation of 225Ac

225Ac is a radio-isotope that can be linked to biological vector molecules to treat certain distributed cancers using targeted alpha therapy. However, developing 225Ac-labelled radiopharmaceuticals remains a challenge due to the supply shortage of pure 225Ac itself. Several techniques to obtain pure 225Ac are being investigated, amongst which is the high-energy proton spallation of thorium or uranium combined with resonant laser ionization and mass separation. As a proof-of-principle, we perform off-line resonant ionization mass spectrometry on two samples of 225Ac, each with a known activity, in different chemical environments. We report overall operational collection efficiencies of 10.1(2)% and 9.9(8)% for the cases in which the 225Ac was deposited on a rhenium surface and a ThO2 mimic target matrix respectively. The bottleneck of the technique was the laser ionization efficiency, which was deduced to be 15.1(6)%.

Automated summary

225Ac is a radio-isotope used in targeted alpha therapy for treating distributed cancers. However, the shortage of pure 225Ac poses a challenge for developing 225Ac-labelled radiopharmaceuticals. One of the investigated techniques to obtain pure 225Ac is high-energy proton spallation of thorium or uranium combined with resonant laser ionization and mass separation. In this study, off-line resonant ionization mass spectrometry was performed on two samples of 225Ac, revealing operational collection efficiencies of 10.1(2)% and 9.9(8%) for different chemical environments.