n.
Metallic chemical element , one of the transition element s, chemical symbol Tc, atomic number 43.
All its isotope s are radioactive (see radioactivity ); some occur in trace amounts in nature as nuclear fission products of uranium . Its isotope technetium-97 was the first element artificially produced (1937; see cyclotron ). Technetium-99, a fission product of nuclear reactors that emits gamma ray s, is the most-used tracer isotope in nuclear medicine . Technetium resembles platinum in appearance and manganese and rhenium in chemical behaviour. It is also used as a metallurgical tracer and in corrosion-resistant products.