Researchers have outlined several neutron- and photon-driven pathways for producing critical medical radioisotopes using fusion energy sources, according to a new preprint posted to arXiv. The paper focuses on creating generator parents for Actinium-225 (${}^{225}$Ac) and Lead-212 (${}^{212}$Pb), two alpha-emitting nuclides with high therapeutic potential but severely limited supply. The proposed methods would utilize the high-energy neutron flux from deuterium-tritium (D-T) fusion reactions to transmute target materials like thorium and protactinium. This approach presents a non-fission-based alternative for isotope production, potentially offering a new economic driver for the development of commercial fusion power plants and dedicated neutron source facilities. Source: arXiv
The most direct route detailed for ${}^{225}$Ac production is the ${}^{230}$Th(n,2n)${}^{229}$Th reaction. The authors calculate that a 10 MW D-T neutron source irradiating a thorium target with a 27% ${}^{230}$Th isotopic fraction for six months would accumulate approximately 250 Curies of ${}^{229}$Th. This quantity of the generator parent, which has a half-life of 7916 years, would be sufficient to supply five million ${}^{225}$Ac dose-equivalents annually at the start of its use. The analysis suggests this level of production requires only about 2 gigawatt-days of cumulative D-T fusion operations, a metric within the operational plans of several near-term fusion pilot plant concepts. The long half-life of ${}^{229}$Th makes it a durable, long-term asset for medical supply chains. Source: arXiv
The most direct route detailed for ${}^{225}$Ac production is the ${}^{230}$Th(n,2n)${}^{229}$Th reaction.
For the production of ${}^{212}$Pb, the paper proposes a different pathway involving thermal-neutron irradiation. By irradiating tens of grams of ${}^{230}$Th in a thermal neutron environment, gram quantities of ${}^{232}$U can be produced. This ${}^{232}$U, in turn, serves as a decades-long source for ${}^{228}$Th, the immediate parent of ${}^{212}$Pb. The authors project that this method could generate enough material for millions of ${}^{212}$Pb dose-equivalents per year. This highlights the versatility of using different neutron energy spectra, where fast neutrons from D-T reactions could be moderated to thermal energies to drive specific reactions, expanding the portfolio of isotopes a single fusion facility could produce. Source: arXiv
The preprint also explores alternate production routes starting from more abundant materials like ${}^{232}$Th. Fusion neutrons can convert ${}^{232}$Th into ${}^{231}$Pa at a rate of 1 to 2 tonnes per gigawatt-year of fusion operation. This manufactured ${}^{231}$Pa can then be irradiated in a separate thermal reactor to produce ${}^{232}$U at a rate of up to 0.4 grams per gram of ${}^{231}$Pa. This two-step process, combining a fusion neutron source with a conventional fission reactor, could significantly broaden the feedstock options for medical isotope generation. Such symbiotic applications could provide early revenue streams for the nascent private fusion industry and justify the construction of dedicated high-flux neutron sources before net-energy-gain power plants are fully realized. Source: arXiv