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

Actinium-225 and213 Bi 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 of225 Ac. The high-energy proton spallation reaction on natural thorium metal targets has been utilized to produce millicurie quantities of225 Ac. The results of sixteen irradiation experiments of thorium metal at beam energies between 78 and 192MeV 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 of225 Ac range from 3.6 to 16.7mb in the incident proton energy range of 78-192MeV. Based on these data, production of curie quantities of225 Ac is possible by irradiating a 5.0gcm-2 232 Th target for 10 days in either BNL or LANL proton irradiation facilities.