Scalable Production of Lead-212 and Actinium-225 Generators with Fusion Neutrons

Abstract

Targeted alpha therapy will require a large expansion of ${}^{212}$Pb and ${}^{225}$Ac production. We propose neutron- and photon-driven routes that convert ${}^{230}$Th, ${}^{231}$Pa, ${}^{232}$Th, and ${}^{237}$Np into generator parents ${}^{228}$Th and ${}^{229}$Th. The most direct ${}^{225}$Ac route is ${}^{230}$Th(n,2n)${}^{229}$Th. A 10 MW deuterium-tritium (D-T) neutron source irradiating thorium with a 27% ${}^{230}$Th isotopic fraction accumulates about 250 Ci of ${}^{229}$Th in six months, initially enough for five million ${}^{225}$Ac dose-equivalents per year, and its 7916 yr half-life makes it useful for millennia. This requires only $\sim$2 gigawatt-days of D-T fusion operations. Thermal-neutron irradiation of tens of grams of ${}^{230}$Th produces gram quantities of ${}^{232}$U, a decades-long source of ${}^{228}$Th for millions of ${}^{212}$Pb dose-equivalents per year. Alternate routes proceed through ${}^{231}$Pa: fusion neutrons produce 1 to 2 tonnes of ${}^{231}$Pa per gigawatt-year from ${}^{232}$Th, and a thermal reactor converts up to 0.4 g of ${}^{232}$U per gram of ${}^{231}$Pa. Each gram of stored ${}^{232}$U produces 10 mg (8.2 Ci) of ${}^{228}$Th per year. Subsequent ${}^{228}$Th(n,$\gamma$)${}^{229}$Th converts 0.07 to 0.34 g of ${}^{229}$Th per gram of ${}^{228}$Th. We also analyze the ${}^{237}$Np(n,2n)${}^{236\mathrm{m}}$Np route to ${}^{228}$Th. These pathways scale from kilowatt to megawatt D-T sources and could secure millions of ${}^{212}$Pb and ${}^{225}$Ac dose-equivalents per year.

arXiv comment18 pages, 15 figures