An assessment of radionuclidic impurities of (210)Po produced via neutron irradiation of (209)Bi for use in targeted alpha-particle radiotherapy.

Radionuclidic impurities of (210)Po prepared by neutron irradiation of (209)Bi via the (209)Bi(n,gamma)(210)Bi reaction were investigated. Following irradiation and ingrowth, a pure (210)Po solution was obtained by sublimation and dissolution. Results were obtained by liquid scintillation (LS) counting, isotope dilution alpha (alpha)-spectrometry, and high-purity germanium gamma-ray spectrometry. No alpha-emitting (3-10MeV) or gamma-emitting (30-3600keV) impurities were detected, with calculated lower limits of detection for impurities of approximately 0.01% (210)Po activity. LS spectra revealed no identifiable beta-emitting impurity. LS sources prepared using Opti-Phase 'Hi Safe' III and Opti-Fluor LS cocktails were stable over a 4-day multi-cycle counting period for (210)Po dissolved in 0.1% trifluoracetic acid (pH approximately 2, water fraction approximately 2%). The radioactivity concentration determined by LS counting was verified by isotope dilution alpha spectrometry. These results suggest that neutron irradiation of (209)Bi (followed by sublimation) can produce (210)Po in a highly pure form that is suitable for radiopharmaceutical preparations.