Patent Number: 052805050
Section: claims

1. A method for producing a selected isotope from a target material which is not normally a solid and which, when bombarded by selected high energy particles, produces the selected isotope, comprising the steps of: forming a frozen layer of the target material on a cooled target surface;  bombarding the target material with said high energy particles for a selected time period, the target material being altered by the bombarding particles to contain a quantity of the isotope; and  extracting the isotope-containing target material.  wherein said bombarding step includes the step of directing a beam of said high energy particle at said interior surface in the direction of said axis, and thus at an angle .theta./2 to the surface.  a target surface;  means for cooling the surface to a temperature below the freezing temperature of the target material;  means for depositing a layer of frozen target material on the surface;  means for bombarding the target material with said high energy particles for a selected time period, the target material being altered by the bombardment to contain a quantity of the selected isotope, and;  means for extracting the isotope-containing target material. 2. A method as claimed in claim 1 wherein said forming step includes the steps of cooling the surface to a temperature below the freezing temperature of the target material, and introducing the target material into the vicinity of said surface in a liquid form. 3. A method as claimed in claim 2, wherein the introducing step includes the step of directing the target material as a jet spray at the surface. 4. A method as claimed in claim 1 wherein said surface is the interior surface of a cone having a central axis, said interior surface extending at an angle .theta./2 to said axis; and 5. A method as claimed in claim 4 wherein said extracting step includes the steps of melting the isotope-containing target material, and extracting the melted material. 6. A method as claimed in claim 5 including the step, performed prior to the melting step, of tilting the cone so that is axis is oriented substantially vertical. 7. A method as claimed in claim 5 wherein said extracting step includes the steps of collecting the melted, isotope-containing target material at the tip of the cone, and forcing the collected material from the cone tip. 8. A method as claimed in claim 1 wherein said selected time period is the time required to obtain a desired quantity of the selected isotope for the particle energy and target material layer thickness utilized. 9. A method as claimed in claim 1 including the step of evacuating the environment in which the surface is located. 10. A method as claimed in claim 1 wherein said extracting step includes the steps of heating the isotope-containing target material to sublimate the material, and extracting the sublimated material. 11. A method as claimed in claim 1 wherein said high energy particles are at an angle to said surface such that the particles pass through a thickness of the target material greater than the thickness of said layer before reaching said surface. 12. A method as claimed in claim 1 wherein said selected isotope is a radioisotope. 13. A method as claimed in claim 12 wherein said radioisotope is .sup.18 F and wherein said frozen target material is .sup.18 0 ice. 14. Apparatus for producing a selected radioisotope from a target material which is not normally a solid and which, when bombarded with selected high energy particles, produces the selected isotope, the apparatus comprising: 15. Apparatus as claimed in claim 14, including a sealed chamber in which said surface is positioned; and wherein said means for depositing includes means for introducing the target material into the chamber in liquid form. 16. Apparatus as claimed in claim 15 wherein said means for introducing includes a nozzle in said chamber for directing the target material as a jet spray at the surface. 17. Apparatus as claimed in claim 16 wherein said nozzle is adjacent to said surface when it is directing target material thereat, and including means for retracting said nozzle when not in use. 18. Apparatus as claimed in claim 14 wherein said surface is the interior surface of a cone having a central axis, said interior surface extending at an angle .theta./2 to said axis. 19. Apparatus as claimed in claim 18, including a sealed chamber, and means for mounting said cone in the chamber with its axis pointed in the direction of the means for bombarding. 20. Apparatus as claimed in claim 19 wherein said means for extracting includes means for melting the isotope-containing target material, and means for extracting the melted material. 21. Apparatus as claimed in claim 20, including means operative prior to said means for melting for tilting the cone so that is axis is oriented substantially vertical. 22. Apparatus as claimed in claim 21 wherein said melted, isotope-containing target material flows from said surface to the tip of the cone, and wherein said means for extracting includes means for forcing the collected target material from the cone tip. 23. Apparatus as claimed in claim 22 wherein said means for forcing includes means for applying positive pressure to the target material in the tip. 24. Apparatus as claimed in claim 22 including means for facilitating the flow of melted target material to said tip. 25. Apparatus as claimed in claim 21 wherein said means for tipping includes means for pivoting the chamber. 26. Apparatus as claimed in claim 18, including means for facilitating the cooling of the cone to dissipate heat resulting from the high energy particles applied thereto by said means for bombarding. 27. Apparatus as claimed in claim 26 wherein said means for facilitating cooling includes at least one fin extending from an exterior surface of said cone. 28. Apparatus as claimed in claim 27 wherein said fins are integral with the cone. 29. Apparatus as claimed in claim 14 wherein said target surface is part of a target structure, and wherein said means for cooling includes means for placing at least a portion of the target structure in contact with a liquid coolant. 30. Apparatus as claimed in claim 29 wherein said liquid coolant is liquid nitrogen. 31. Apparatus as claimed in claim 14 wherein there is a minimum depth t.sub.b' that the high energy particles must pass through the deposited frozen target material layer to produce a desired quantity of isotope from the target material, and wherein the cone angle .theta. and the layer thickness t.sub.i are selected such that t.sub.i .about.t.sub.b' sine .theta./2. 32. Apparatus as claimed in claim 14 wherein the extracting means includes means for heating the isotope-containing target material to sublimate the material, and means for extracting the sublimated material. 33. Apparatus as claimed in claim 14 wherein said high energy particles are at an angle to said surface such that the particles pass through a thickness of the target material greater than the thickness of said layer before reaching said surface. 34. Apparatus as claimed in claim 14 wherein said selected isotope is a radioisotope. 35. Apparatus as claimed in claim 34 wherein said selected radioisotope is .sup.18 F, and wherein said frozen target is .sup.18 0-ice.