Chemical element with atomic number of 43
Emilio Gino Segrè
Technetium (chemical symbol - Tc, from Lat. Technetium) is a chemical element of the 7th group (according to the outdated classification - the seventh group of the secondary subgroup, VIIB), the fifth period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 43.
A simple substance technetium is a radioactive transition metal of silver-gray color. The lightest element with no stable isotopes.  The first of the synthesized chemical elements.
Only about 18,000 tons of naturally formed technetium could be found at any given time in the earth's crust before the beginning of the nuclear era. Natural technetium is a product of spontaneous fission of uranium ore and thorium ore or a product of neutron capture in molybdenum ores. The most common natural isotope is 99Tc. The rest of the technetium on Earth is produced synthetically as a product of fission of uranium-235 and other fissile nuclei in nuclear reactors of all types (energy, military, research, propulsion