Abstract: A generator for liquid containing .sup.99m Tc has an adsorbant bed of alumina, zirconia or the like and has associated therewith a quantity of an electron scavenging compound of a rare earth, silver or gold so as to maintain elution efficiency during the working life of the generator. The compound may be a rare earth oxide such as ceric oxide typically present as a coating on alumina particles in an amount of about 0.1% by weight or a compound such as silver chloride present in quantities typically of about 5%. The eluant may be sodium or potassium perchlorate in water.