The first artificially produced element and a radioactive fission product of uranium. technetium has the atomic symbol Tc, atomic number 43, and atomic weight 98.91. All technetium isotopes are radioactive. technetium 99m (m=metastable) which is the decay product of molybdenum 99, has a half-life of about 6 hours and is used diagnostically as a radioactive imaging agent. technetium 99 which is a decay product of technetium 99m, has a half-life of 210,000 years.