Accelerator-based method of producing isotopes

A subcritical method to produce Mo-99 comprising:

• a) supplying a proton beam having an energy of up to 400 MeV;
• b) directing the proton beam at a downstream core of low-enriched uranium, said core comprised of:
• a plurality of coated cylindrical foils, said coated cylindrical foils arranged in an array of coaxial cylinders with said cylinders having a common axis orthogonal to the beam direction and with said cylinders decreasing in diameter and increasing in height from the outermost concentric cylinder to the innermost concentric cylinder such that the plurality of coated cylindrical foils forms a substantially spheroidal shape and wherein said core is immersed in water and surrounded by a first shell of low-enriched uranium, a second shell of beryllium, and a third shell of carbon;
• c) placing a high-atomic-number (“high-Z”) material downstream of the proton beam and upstream of the core;
• d) exposing the high-Z material to the proton beam so as to produce a flux of neutrons in the direction of the downstream core, and producing on average greater than 10 fissions in the core for each proton of the proton beam;
• e) causing the neutrons to contact the low-enriched uranium and causing fissions therein for a time sufficient to generate desired quantities of Mo-99 from the low-enriched uranium;
• and
• f) extracting said Mo-99 from said core.