Techniques for on-demand production of medical radioactive iodine isotopes including I-131
A system for radioisotope production uses fast-neutron-caused fission of depleted or naturally occurring uranium targets in an irradiation chamber. Fast fission can be enhanced by having neutrons encountering the target undergo scattering or reflection to increase each neutron's probability of causing fission (n, f) reactions in U-238. The U-238 can be deployed as one or more layers sandwiched between layers of neutron-reflecting material, or as rods surrounded by neutron-reflecting material. The gaseous fission products can be withdrawn from the irradiation chamber on a continuous basis, and the radioactive iodine isotopes (including I-131) extracted.
1. A method for producing radioactive iodine comprising:
providing a volume of non-enriched uranium (“NEU”) material in an irradiation chamber, the irradiation chamber having a gas inlet port and a gas outlet port;
providing one or more non-moderating neutron-reflecting regions disposed in the irradiation chamber;
irradiating the uranium material with neutrons provided by a compact, stand-alone neutron generator to cause fission reactions to occur in the uranium material, wherein:
the neutrons are provided at an energy above a fast fission threshold for U-238,
the one or more non-moderating neutron-reflecting regions are configured to increase the path length traveled by at least some of the neutrons before those neutrons leave the irradiation chamber,
at least some of the fission reactions lead to the production of radioactive iodine, and
at least some of the radioactive iodine sublimates in the irradiation chamber;
during irradiation, introducing a carrier gas into the gas inlet port to mix with the sublimated radioactive iodine and form a gas mixture;
withdrawing the gas mixture from the gas outlet port; and
separating at least some of the radioactive iodine from other components of the gas mixture.
2. The method of claim 1 wherein at least a portion of the gas mixture is returned to the gas inlet port after separation of the radioactive iodine.
3. The method of claim 1 wherein separating at least some of the radioactive iodine includes using a silver zeolite trap.
4. The method of claim 1 , and further comprising, after an irradiation period:
removing the NEU material from the irradiation chamber;
dissolving the NEU material in a solvent, thereby releasing additional sublimated iodine as part of an additional gas mixture; and
separating at least some of the additional radioactive iodine from other components of the additional gas mixture.
5. The method of claim 1 wherein the NEU material consists of one of the following forms: solid material, crushed solid material, metallic shavings, metallic filings, sintered pellets, liquid solutions, molten salts, molten alloys, and slurries.
6. The method of claim 1 wherein the NEU material comprises material in granular form.
7. The method of claim 1 wherein the NEU material comprises material in molten form.
8. The method of claim 1 wherein the NEU material comprises material in solid form.
9. The method of claim 1 wherein the NEU material comprises material formed into multiple elongate rods.
10. The method of claim 1 wherein the compact, stand-alone neutron generator generates neutrons above an energy of 0.8 MeV.
11. The method of claim 1 wherein the one or more non-moderating neutron-reflecting regions disposed in the irradiation chamber comprise multiple elongated parallel non-moderating neutron-reflecting regions disposed within the irradiation chamber, wherein each of the multiple elongated parallel non-moderating neutron-reflecting regions has an interior bore for receiving the NEU material.
12. The method of claim 1 wherein the at least one non-moderating neutron-reflecting region disposed within the irradiation chamber comprises multiple non-moderating neutron-reflecting regions.
13. The method of claim 1 wherein the NEU material comprises depleted uranium.
14. The method of claim 1 wherein the compact, stand-alone neutron generator comprises a linear accelerator-type neutron generator.
15. The method of claim 12 wherein the at least one non-moderating neutron-reflecting region disposed within the irradiation chamber further comprises a non-moderating neutron-reflecting wall interior to the irradiation chamber that is exterior to the multiple non-moderating neutron-reflecting regions.