Microstructure engineering of actinide refractory materials for ISOL@MYRRHA day-1 target operation

The future ISOL@MYRRHA will be able to produce different radioactive isotopes for applications in the field of nuclear physics, condensed-matter physics, biology, nuclear medicine and others. The used Isotope Separation On-Line (ISOL) technique relies on a series of successive steps starting with the irradiation of a target material by a proton beam where the impact of the protons induces nuclear reactions through which the radioisotopes are produced. During irradiation, these radioisotopes have to be released from the target, by keeping it at temperatures in the range of ~2000°C in vacuum. When produced in the bulk of the material, the isotopes have to diffuse out of the target material grains and effuse throughout its interconnected pore network to escape from the target. After that, the isotopes are directed towards an ion source where they are selectively ionized, extracted and accelerated towards an electromagnetic mass separator for further purification before being delivered to the end-users as a so-called Radioactive Ion Beam (RIB). Successful operating facilities, like ISOLDE at CERN and ISAC at TRIUMF, can produce up to about 1000 different RIBs from up to 75 chemical elements.

This work focuses on the target release efficiency, one of the most important and most limiting steps of an ISOL facility. This is normally worked out through carefully selecting the target material compound (e.g. oxide, carbide or metal form) and engineer a microstructure which contains an interconnected pore network. Additionally this microstructure must be stable under proton beam irradiation and high ISOL operation temperatures (up to 2000°C), where target material degradation (i.e. through sintering) brings RIB yield reduction over time. Actinide oxides are suggested as one of the first target materials for the ISOL@MYRRHA operation, although they have been discarded in the past for ISOL operation due to their high sintering rates. In this work, actinide oxide materials with open porous structures with small grain sizes will be attempted to be stabilized at the highest possible temperature and tested for release by irradiation with a proton beam in an external facility.