Abstract A novel method is suggested for producing a new positron (e +) emitting isotope in a nuclear reactor with application to slow e + beams. The initial radiated sample is 124Xe which is transformed to 126I by two neutron absorptions and an intermediate decay. Over 25 Ci of positrons with a specific activity of 25 Ci gm can be produced by this technique, allowing the generation of a slow e + beam of over 4 × 10 7 e + cm 2 −s. As discussed in the conclusion, specific activities approaching 200 Ci gm should be for activation cells are presented, one with Xe in the gas phase, the other with solid Xe. Both designs allow the easy separation of the 126I from other contaminants, permitting the production of a pure, high specific activity source.