Patent Number: 044877382
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with the preferred embodiment of the method of the present invention, a target is prepared by pressing approximately 90 grams of powdered zinc oxide into a solid disc contained inside a high purity aluminum ring. High purity aluminum is used to avoid the presence of copper contaminants in the aluminum, which would migrate into the target during irradiation and contaminate the spallogenic copper formed from the ZnO. The target is placed in an aluminum target enclosure for introduction into the target region of the linear accelerator. The ZnO target is irradiated with a proton beam having an energy of approximately 800 MeV and a beam current on the order of 300 microamperes, for a period on the order of 60-70 hours. The spallation cross section of the ZnO target for .sup.67 Cu is approximately 5.35 millibarns. Under such conditions, an amount of .sup.67 Cu on the order of 1.0 curie (approximately 1.3 micrograms) is formed, together with approximately 34 other identifiable nuclides, which are presented in FIG. 1. The only other isotopes of copper which are produced in measurable quantities are the short-lived isotopes .sup.64 Cu and .sup.61 Cu. In accordance with the preferred method of chemical separation, which is illustrated schematically in FIG. 2, the irradiated ZnO target is removed from the aluminum ring and dissolved in a concentrated HCl solution. To this acid solution is added approximately 20 milligrams of Pd.sup.+2 (added as 2.5 cc of palladium chloride solution containing 8.5 mg Pd.sup.+2 /cc). Approximately one-half to two grams of finely powdered metallic zinc are then added to the acid solution. The zinc is oxidized to Zn.sup.+2, which reduces the Pd.sup.+2 to metallic palladium and also reduces the spallogenic Cu.sup.+2 in solution to metallic copper. The metallic palladium precipitates as a finely divided solid and quantitatively scavenges from solution the spallogenic copper. The metal precipitate is then redissolved in an acid solution and the palladium and copper are once again precipitated, this time by sparging the acid solution with gaseous hydrogen sulfide. The sulfide precipitate is then dissolved once again in an acid solution, and the palladium and copper in solution are separated by chromatography on an anion exchange column. In an alternative variation of the chemical separation step of the method, the palladium is precipitated by the introduction of powdered zinc as above, and the precipitated palladium/copper mixture is subsequently passed through a series of three ion exchange columns, as illustrated in FIG. 3. In accordance with the latter alternative method, the mixture of metallic palladium and copper, which also contains traces of spallogenic cobalt, manganese and vanadium, is collected by filtration and dissolved in an acid solution consisting of approximately 9 ml concentrated HCl and 1 ml concentrated HNO.sub.3. This solution is passed through a cation exchange resin column, preferably consisting of purified Dowex AG (Analytical Grade) 50.times.4 (sulfonic acid resin type column), which is commercially available from Bio-Rad, Inc. of Richmond, Calif. This column operates to capture any gallium that may be present with the spallogenic copper. In this regard, it is noted that .sup.67 Ga, which is a spallogenic reaction product, has a gamma emission spectrum which is nearly identical to that of .sup.67 Cu, thus making it difficult to detect in the initial stages of chemical separation. The cation column also collects .sup.51 Cr, which is also present in trace amounts in the reaction products. The eluate solution, which contains Cu as well as Pd in essentially concentrated HCl, is introduced untreated into a second column which is an anion exchange column, and which preferably consists of purified Dowex AG 1.times.8 quaternary amine resin, a strong base anion resin. The Cu.sup.+2, together with the Pd.sup.+2, is initially bound to the anion exchange resin. The Cu.sup.+2 is then selectively eluted from the column with 2M HCl, leaving behind the Pd.sup.+2 as a palladium chloro complex. The eluted solution, containing Cu.sup.+2 and having a volume on the order of 15 ml, is evaporated to dryness and the residue subsequently dissolved in a solution consisting of 80% (by volume) acetone and 20% water, acidified to 0.1 molar HCl. This solution is then passed through a third column containing a Bio-Rad Dowex AG 50.times.8 cation exchange resin. The Cu is absorbed on this column initially, together with any Co.sup.+2 or Mn.sup.+2 that may be present. The Cu.sup.+2 is then selectively eluted with an acetone/water solution acidified to 0.5M HCl. The use of this third column to remove traces of Mn and Co is not mandatory to the practice of the method, but is preferred when the .sup.67 Cu is to be used over a period longer than several half-lives, since in such circumstances the activities of trace amounts of spallogenic radioactive Co and Mn isotopes become large relative to the activity of the .sup.67 Cu and thereby interfere with measurement of .sup.67 Cu gamma ray emissions. The 0.5M HCl/acetone/water solution containing the spallogenic .sup.67 Cu is sufficiently pure for use in medical applications. However, if desired, this solution may be evaporated to dryness and the residue redissolved in 0.1M HCl, which renders the solution more desirable for some medical applications. The yield of .sup.67 Cu by this version of the method is on the order of 50% of the spallogenic .sup.67 Cu originally produced. The only impurities that have been detected are trace amounts of inactive Zn and inactive Cu. The spallogenic Cu includes some .sup.64 Cu, which has a half-life of 12.7 hours and which largely decays by the time the .sup.67 Cu-bearing solution is shipped and prepared for use. Also present in the spallogenic Cu is .sup.61 Cu, which decays even faster with its half-life of 3.3 hours. EXAMPLE 1 In an actual demonstration of the method, a spallation target consisting of 79.2 grams of powdered zinc oxide was bombarded with 800 MeV protons for a period of 93.4 hours in the linear accelerator of the Los Alamos Meson Physics Facility. The beam current averaged 423 microamps and resulted in a total integrated irradiation of 39,531 microamp-hours. A yield of 3.11 curies of .sup.67 Cu was obtained, using the alternative separation process described above. Also obtained were 10.0 curies of .sup.64 Cu and an undetermined amount of .sup.61 Cu. Additionally, it was determined that 3.4 curies of .sup.62 Zn and 0.96 curie of .sup.48 V were produced, as well as other unidentified nuclides. EXAMPLE 2 In another demonstration of the method, also using the alternative 3-column separation process, a target consisting of 75.7 grams of zinc oxide was irradiated with 800 MeV protons for a period of 23.9 hours. The beam current was approximately 386 microamps and provided an integrated irradiation of 9,219 microamp-hours. A yield of 1.0 curie of .sup.67 Cu was obtained. Also obtained were 9.4 curies of .sup.64 Cu, 11.9 curies of .sup.61 Cu, 2.5 curies of .sup.62 Zn and 0.22 curie of .sup.48 V. EXAMPLE 3 In another demonstration, a target consisting of 73.2 grams of zinc oxide was irradiated with a total irradiation of 15,643 microamp-hours. The target was then dissolved in 160 cc of concentrated HCl. To this solution was added 2.5 cc of a PdCl.sub.2 solution containing 8.5 mg/cc Pd. 0.5 gm of zinc dust was added to effect reduction of the Pd and spallogenic Cu in solution. The reduced metal was collected by filtration and dissolved in a solution consisting of 10 cc concentrated HCl and 1 cc concentrated HNO.sub.3. The resulting solution was heated and stirred and sparged with hydrogen sulfide for several minutes. The resulting precipitate was collected by filtration and dissolved in a HCl/HNO.sub.3 solution as described above. This solution was diluted with 9M HCl, which was used to rinse the filter, to obtain a solution approximately 9M in HCl. The Cu-bearing 9M HCl solution was added to an AG 1.times.8 anion exchange column. The column was washed with 2 to 3 column volumes of 9M HCl. The copper was then eluted from the column with 2M HCl, leaving the Pd behind on the column. The resulting solution was determined to contain 201 millicuries of .sup.67 Cu. The foregoing descriptions of alternative preferred embodiments of the method of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The particular embodiment described and illustrated were selected in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.