A composite target of a radium salt and a soft metal matrix for production of Ac-225 with a proton or electron accelerator

The production of 225Ac using either a proton or an electron accelerator requires a target of 226Ra. Radium metal is difficult to work with and so a radium salt, such as radium carbonate, is preferred as a target material. Normally available as a powder, the average density of the powder is low, and the thermal conductivity is poor, thus limiting the beam power that can be dissipated in the target. This work proposes the creation of a solid mixture of a radium salt powder with a metal matrix. Although aluminum powder has been used in similar applications, we suggest that indium powder is a good choice for the metal matrix in the case of radioactive radium salts. The target can be formed with low die pressure, thus simplifying the hot cell equipment needed for target preparation. We describe how the solid mixture can be formed, measure its thermal conductivity, and compare the value to model estimates. We calculate the yield of 225Ac under different scenarios. Calculations show that the radioactive isotopes of indium should not produce significant handling challenges. Thermal modeling indicates that the target temperature will be below the melting point of indium. The Fluka Monte Carlo code predicts that a target with 1/2 g of radium will produce 80 GBq for a 10-day irradiation with 3 kW of 24 MeV protons and 47 GBq of 225Ra for a 25 MeV, 20 kW electron beam. A target of one gram of radium will produce about 80 GBq with electrons.