A Composite Target of a Radium Salt and a Soft Metal Matrix for Production of Ac-225 with a Proton or Electron Accelerator

TL;DR

This paper proposes a novel composite target made of radium salt powder and indium metal matrix for efficient production of Ac-225 using proton or electron accelerators, improving thermal management and yield.

Contribution

It introduces a new composite target design with indium powder that simplifies preparation and enhances heat dissipation for Ac-225 production.

Findings

Thermal conductivity of the composite target is measured and modeled.

The target can produce approximately 80 GBq of Ac-225 after 10 days of irradiation.

The target temperature remains below indium's melting point during operation.

Abstract

The production of 225Ac using either a proton or 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 good choice for the metal matrix in the case of radioactive radium salts. The target can be formed with low die pressure without any need for heating, 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 produced during the irradiation should not produce significant handling challenges post-irradiation. For the proposed target geometry and beam parameters, thermal modelling indicates that the target temperature will be below the melting point of indium and the heat flux from the surfaces will be manageable. Thermal resistance at the target interfaces is shown to have a large effect on the target temperature. Using indium powder to form the mixture, occupying about 40 % of the target volume, we find that the yield of 225Ac is 80 GBq (2 Ci) for a 10-day irradiation with a 24 MeV, 3 kW proton beam and approximately the same for three milkings of 225Ra after a 10-day irradiation with a 25 MeV, 20 kW electron beam.