Study of medical radioisotope production of Ac-225 by proton accelerator

²²⁵Ac radionuclides have shown great potential for use as radiopharmaceuticals in cancer therapy by conjugation them with carrier molecules due to their strong cytotoxicity, suitable half-life, and ability to be used as ²¹³Bi generators. The production of ²²⁵Ac via bombardment of ²³²Th targets with accelerated protons is currently the most widely used method in the world. In order to better quantify the achievable yields and radiopurity, this production process is simulated in this study. Firstly, the formation cross sections of ²²⁵Ac、²²⁶Ac、²²⁷Ac、²²⁵Th、²²⁹Pa、²²⁵Ra、²²⁹Th, and ²²⁷ Ra by proton incident on thorium with energies up to 500 MeV is calculated using Monte Carlo transport codes PHITS in combination with different spallation reaction models(INCL4.6 + GEM, Bertini + GEM, JAM + GEM), and are compared them with the available experimental data as well as the nuclear data given by TENDL-2021. Then, based on the predicted and experimental cross sections, the production yields and purity of ²²⁵Ac and other co-produced medical isotopes during and after irradiation are investigated.