text: The feasibility of Tc production with the 22-MeV-proton bombardment of a Mo target in medical cyclotrons was demonstrated in 1971. The recent shortages of Tc reignited the interest in the production of "instant" 99mTc by proton bombardment of isotopically enriched Mo targets (>99.5%) following the reaction Mo(p,2n)Tc. Canada is commissioning such cyclotrons, designed by Advanced Cyclotron Systems, for Tc production at the University of Alberta and the Université de Sherbrooke, and is planning others at the University of British Columbia, TRIUMF, University of Saskatchewan and Lakehead University.
  A particular drawback of cyclotron production via (p,2n) on Mo is the significant co-production of  Tc. The preferential in-growth of this nuclide occurs due to the larger reaction cross-section pathway leading to the ground state, which is almost five times higher at the cross-section maximum in comparison with the metastable one at the same energy. Depending on the time required to process the target material and recovery of Tc, the amount of Tc  relative to Tc will continue to decrease, in turn reducing the specific activity of Tc available. It has been reported that ingrowth of Tc as well as the presence of other Tc isotopes can negatively affect subsequent labelling and/or imaging; however, the use of high purity Mo targets, specified proton beam energies, and appropriate time of use have shown to be sufficient for yielding Tc from a cyclotron comparable to that from a commercial generator.  Liquid metal molybdenum-containing targets have been proposed that would aid in streamlined processing, ensuring better production yields. A particular problem associated with the continued reuse of recycled, enriched Mo targets is unavoidable transmutation of the target as other Mo isotopes are generated during irradiation and cannot be easily removed post-processing.