Techniques for on-demand production of medical isotopes such as mo-99/tc-99m and radioactive iodine isotopes including i-131

Abstract

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 The gaseous fission products can be withdrawn from the irradiation chamber on a continuous basis, and the radioactive iodine isotopes (including I-131) extracted.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 - 20 . (canceled) 
     
     
         21 . A method for producing radioisotopes comprising:
 introducing non-enriched uranium (“NEU”) material into a an irradiation chamber, the irradiation chamber having one or more walls formed of neutron-reflecting material;   irradiating the NEU material with neutrons having energies above 800 keV to cause fast fission reactions to occur in the NEU material and generate fission products, wherein:
 at least some neutrons from the irradiating are reflected from at least one of the one or more walls, thereby increasing the path length over which those neutrons are in the NEU material, and 
 the increased path length increases the probability that those neutrons in the NEU material will cause fast fission reactions; and 
   extracting the fission products from the NEU material.   
     
     
         22 . The method of  claim 21  wherein one of the fission products extracted comprises at least one of molybdenum-99 (Mo-99) and technetium-99m (Tc-99m). 
     
     
         23 . The method of  claim 21  wherein one of the fission products extracted comprises at least one of iodine 131 (I-131) and iodine 132 (I-132). 
     
     
         24 . The method of  claim 21  wherein the NEU material in the irradiation chamber occupies a single spatially contiguous region. 
     
     
         25 . The method of  claim 21  wherein the NEU material in the irradiation chamber occupies multiple spatially disjoint regions. 
     
     
         26 . The method of  claim 21  wherein the one or more walls formed of neutron-reflecting material comprise at least one internal wall of the irradiation chamber. 
     
     
         27 . The method of  claim 21  wherein the one or more walls formed of neutron-reflecting material comprise an outer wall that surrounds all the NEU material in the irradiation chamber. 
     
     
         28 . The method of  claim 21  wherein the one or more walls formed of neutron-reflecting material comprise:
 at least one internal wall of the irradiation chamber; and 
 an outer wall that surrounds all the NEU material in the irradiation chamber. 
 
     
     
         29 . A method for producing radioisotopes comprising:
 providing a volume of NEU material;   interspersing the NEU material with neutron-reflecting material;   surrounding the volume of NEU material with additional neutron-reflecting material;   surrounding the additional neutron-reflecting material with neutron-absorbing material; and   irradiating the NEU material with neutrons having energies above a fission threshold to cause fast fission reactions to occur in the NEU material and generate fission products;   wherein,
 for at least some neutrons, the neutron-reflecting material prolongs the time that those neutrons remain within the volume of NEU material, thereby increasing the number of fast fission reactions caused by those neutrons before those neutrons encounter the neutron-absorbing material. 
   
     
     
         30 . The method of  claim 29 , and further comprising extracting the fission products from the NEU material. 
     
     
         31 . The method of  claim 30  wherein extracting at least one of the fission products requires removing the NEU material from the irradiation chamber. 
     
     
         32 . The method of  claim 30  wherein extracting at least one of the fission products does not require removing the NEU material from the irradiation chamber. 
     
     
         33 . An apparatus for producing radioisotopes comprising:
 a fast neutron generator; and   a plurality of spaced shells made of neutron-reflecting material, wherein:   the shells include an outermost shell,   the shells surround the neutron generator, and   the spacing between adjacent shells provides a number of regions configured to receive NEU for irradiation by neutrons generated by the neutron generator.   
     
     
         34 . The apparatus of  claim 33  wherein the outermost shell is at thicker than the remaining shell or shells. 
     
     
         35 . The apparatus of  claim 33 , and further comprising an outer containment vessel having one or more walls made of neutron-absorbing material to absorb neutrons passing out of the outermost shell. 
     
     
         36 . The apparatus of  claim 35  wherein the walls of the outer containment vessel are spaced from the outermost shell to limit the likelihood that neutrons scattered or reflected from the walls of the outer containment vessel will encounter the outermost shell. 
     
     
         37 . The apparatus of  claim 33  wherein the neutron generator provides neutrons having energies of at least 10 MeV.