the chemical element with atomic number 43 and the symbol Tc. It is the lowest atomic number element without any stable isotopes; every form of it is radioactive, meaning it gives off atomic particles. Nearly all technetium is produced synthetically, and only minute amounts are found in nature. Naturally occurring technetium occurs as a spontaneous fission product in uranium ore or by neutron capture in molybdenum ores. The chemical properties of this silvery gray, crystalline transition metal are intermediate between rhenium and manganese.