Gallium-68 generator
A Germanium-68/Gallium-68 Generator is a device used to extract the positron-emitting isotope 68Ga of gallium from a source of decaying germanium-68. The parent isotope 68Ge has a half-life of 271 days and can be easily utilized for in-hospital production of generator produced Ga-68. Its decay product gallium-68 (with a half-life of only 68 minutes, inconvenient for transport) is extracted and used for certain positron emission tomography nuclear medicine diagnostic procedures, where the radioisotope's relatively short half-life and emission of positrons for creation of 3-dimensional PET scans, are useful.
The parent isotope germanium-68 is the longest-lived (271 days) of the radioisotopes of germanium. It has been produced by several methods. In the U.S., it is primarily produced in proton accelerators: At Los Alamos National Laboratory, it may be separated out as a product of proton capture, after proton irradiation of Nb-encapsulated gallium metal. At Brookhaven National Laboratories, 40 MeV proton irradiation of a gallium metal target produces germanium-68 by proton capture and double neutron knockout, from gallium-69 (the most common of two stable isotopes of gallium). This reaction is: Ga-69(p,2n)Ge-68.
A Russian source produces germanium-68 from accelerator-produced helium ion (alpha) irradiation of zinc-66, again after knockout of two neutrons, in the nuclear reaction Zn-66(α,2n)Ge-68.
When loaded with the parent isotope germanium-68, these generators function similarly to technetium-99m generators, in both cases using a process similar to ion chromatography. The stationary phase is either metal-free or alumina, TiO2 or SnO2, onto which germanium-68 is adsorbed. The use of metal-free columns allows direct labeling of Ga-68 without prepurification, hence making production of gallium-68-radiolabeled compounds more convenient. The mobile phase is a solvent able to elute (wash out) gallium-68 (III) (68Ga3+) after it has been produced by electron capture decay from the immobilized (absorbed) germanium-68.
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