Patent Number: 056152388
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radioactive isotope production target and a method for fabricating a radioactive isotope production target and more specifically to a 99Mo production target and a method for fabricating a 99Mo production target using low enriched uranium. 2. Background of the Invention The use of radioactive isotopes is widespread, and includes applications in such diverse fields as industrial flow rate processes environmental investigations and medicine. These radioisotopes are produced primarily by bombarding highly enriched uranium (HEU), or .sup.235 U with neutrons to produce the daughters. While the demand for radioisotopes continues to increase, the use of HEU continues to be discouraged, primarily as HEU can be reprocessed for nuclear weaponry development. Since the United States desires to curtail the export of HEU, it is necessary to find a substitute target material. One of the major isotopes used in medicine is Technetium-99m, primarily as this isotope has a short-lived half-life of approximately six hours. Technetium-99m for medical purposes is a decay product of .sup.99 Mo, which is produced in research reactors from the fissioning of .sup.235 U or from neutron capture in .sup.98 Mo to make the heavier .sup.99 Mo. .sup.99 Mo has a half-life of 66 hours. .sup.99 Mo is produced using a variety of target designs that contain highly enriched uranium (HEU) of approximately 93 percent .sup.235 U. These designs include cladding shaped as plates, rods and cylinders with uranium material inserted therein Fuel plate designs utilize a sandwich configuration wherein the fissionable material in the form of a wire or a "meat" matrix resides between two plates of nonfissionable material, such as zirconium, aluminum, nickel, or alloys thereof. The advantage of these designs is efficient heat transfer throughout the target. A disadvantage of these plate designs is the need to dissolve the matrix with high volumes of solution to obtain the fission products. Such processes result in product being lost and/or further decaying prior to use. In addition, many plate designs require the use of highly enriched uranium. Fuel rod designs (U.S. Pat. Nos. 3,799,883 and 3,940,318) eliminate those losses experienced when processing the products of HEU fission from plate configurations. Such HEU target rods comprise a hollow cylindrical can with a thin layer of UO.sub.2 coated to the inside wall. Molybdenum recovery is accomplished by adding an acid solution into the target cylinder to dissolve the irradiated UO.sub.2 from the cylinder wall for later processing. However, these rod configurations are limited in that they can accommodate only relatively thin layers of UO.sub.2 coating, of approximately 0.001 inches. Such thicknesses can result in reasonable yields of .sup.99 Mo if HEU is employed as the fissionable material, but not if low enriched uranium (LEU) is used. Approximately five to six times the uranium must be processed and recovered for the same .sup.99 Mo yield obtained in HEU processes. However, increasing the thickness of LEU coatings in rod configurations does not work, as flaking of the material off the inside of the cylinder occurs at effective thicknesses beginning at approximately 0.002 inches. A need exists in the an for a .sup.99 Mo target wherein said target exhibits good heat transfer, has low chemical processing requirements, and incorporates simple design configurations. Such a target must use only low enriched uranium as fissionable material. SUMMARY OF THE INVENTION It is an object of the present invention to provide a radioisotope production target and a method for producing same which overcomes many of the disadvantages of the prior art. It is another object of the present invention to economically provide a relatively simple radioisotope production target. A feature of the invented product is the use of easily removable, low enriched fissionable material. An advantage of the invented product and process is the elimination of complicated fabrication processes and chemical processing steps, thereby affording developing nations the opportunity to produce radioisotopes. Yet another object of the present invention is to provide a radioisotope production target without using high enriched uranium. A feature of the invention is using low enriched uranium as a fissionable material. An advantage of the invention is minimizing export and usage of high enriched uranium thereby maximizing both material handling safety and security against pro-nuclear weapon nations. Still another object of the present invention is to provide a method for fabricating a radioisotope production target using fabrication techniques that do not require bonding the fissionable material with target cladding. A feature of the invention is using mechanical compression forces only to conjoin elements of the invention. An advantage of the invention is the elimination of processes heretofore necessary to separate fissionable materials from nonfissionable materials after irradiation. Briefly, the invention provides for a radioisotope production target comprising an inner cylinder having an outer surface, a first end, and a second end, a foil of fissionable material circumferentially contacting the outer surface of the inner cylinder so as to substantially cover the outer surface of the inner cylinder, and an outer hollow cylinder having an inner surface, a first end, and a second end, said inner surface of the outer hollow cylinder adapted to receive the substantially foil covered inner cylinder and compress tightly against the foil to provide good mechanical contact therewith. The invention also provides for a method for fabricating a primary target for the production of fission products comprising choosing a first substrate having a first substrate first surface, a first substrate second surface, a first substrate peripheral edge, and a first substrate predetermined thickness, preparing the first substrate first surface to receive a foil of fissionable material, said foil of fissionable material having a first foil surface, a second foil surface, and a predetermined thickness, contacting the foil first surface with the first substrate first surface so as to allow for later removal of the foil from the first substrate, choosing a second substrate having a second substrate first surface, a second substrate second surface, a second substrate peripheral edge, and a second substrate predetermined thickness, preparing the second substrate first surface to receive the foil second surface so as to allow for later removal of the foil from the second substrate; attaching the first substrate peripheral edge to the second substrate peripheral edge such that the first substrate second surface and the second substrate second surface are exposed to ambient atmosphere and the foil is sandwiched between the first substrate and second substrate to prevent foil exposure to ambient atmosphere, and compressing the exposed first substrate second surface and the second substrate second surface to assure snug mechanical contact between the foil and the first substrate first surface and between the foil and the second substrate first surface.