Production of 225Ac and 223Ra by irradiation of Th with accelerated protons

The possibility of producing ²²⁵Ac and ²²³Ra by irradiation of natural ²³²Th with medium-energy protons was examined. Thorium foils were irradiated with 90-, 110-, and 135-MeV protons at the accelerator of the Institute for Nuclear Research, Russian Academy of Sciences, in Troitsk (Moscow oblast). The cumulative production cross sections for ²²⁵Ac were 6.7 ± 0.9, 9.8 ± 1.9, and 13.9 ± 1.5 mb, and for ²²⁷Th (²²³Ra precursor), 43 ± 5, 37 ± 6, and 35 ± 4 mb, respectively. Based on the experimental data and theoretical calculations, the possible yields of ²²⁵Ac and ²²³Ra in irradiation of thick thorium targets at various accelerators were determined. An efficient procedure was suggested for isolating the products from the irradiated targets: ²²⁵Ac, by liquid extraction and extraction chromatography, and ²²³Ra, by sublimation from a thorium-lanthanum melt followed by thermochromatographic separation in metallic titanium columns and extraction-chromatographic isolation of radium. The procedure allows production of large (units of curies) amounts of radiochemically pure ²²⁵Ac and ²²³Ra, which is promising for wide use of these radionuclides in nuclear medicine.