Large scale accelerator production of 225Ac: Effective cross sections for 78–192 MeV protons incident on 232Th targets

Actinium-225 and 213Bi have been used successfully in targeted alpha therapy (TAT) in preclinical and clinical research. This paper is a continuation of research activities aiming to expand the availability of 225Ac. The high-energy proton spallation reaction on natural thorium metal targets has been utilized to produce millicurie quantities of 225Ac. The results of sixteen irradiation experiments of thorium metal at beam energies between 78 and 192 MeV are summarized in this work. Irradiations have been conducted at Brookhaven National Laboratory (BNL) and Los Alamos National Laboratory (LANL), while target dissolution and processing was carried out at Oak Ridge National Laboratory (ORNL). Excitation functions for actinium and thorium isotopes, as well as for some of the fission products, are presented. The cross sections for production of 225Ac range from 3.6 to 16.7 mb in the incident proton energy range of 78–192 MeV. Based on these data, production of curie quantities of 225Ac is possible by irradiating a 5.0 g cm−2 232Th target for 10 days in either BNL or LANL proton irradiation facilities.