The only radioisotope of gallium that is presently used is gallium-67, which is produced in a cyclotron by proton bombardment of a zinc metal target according to the 68Zn(p,2n)67Ga nuclear reaction. Gallium-67 (ix/2 = 78.2 hours) decays by EC to stable zinc-67 with principal y-ray emissions of 93 keV (38%), 185 keV (24%), and 300 keV (16%). The radiotracer is isolated by dissolution of the target in hydrochloric acid followed by isopropyl ether extraction of the gallium-67 from the zinc and other impurities. Gallium-67 is back-extracted from the isopropyl ether into 0.2 M hydrochloric acid, evaporated to dryness, and dissolved in sterile, pyrogen-free 0.05 M hydrochloric acid.7 Gallium is an amphoteric element that acts as a metal at low pH but forms insoluble hydroxides when the pH is raised above 2 in the absence of chelating agents. At high pH, gallium hydroxide acts as a nonmetal and dissolves in ammonia to form gallates. Gallium forms compounds of oxidation states +1, +2, and +3; however, only the Ga+3 state is stable in aqueous solutions.
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