The atomic number of the first artificially produced element, technetium, is 43. Atomic number counts protons, so every technetium atom has 43 protons in its nucleus.
Technetium was created and identified in 1937 by Italian chemists Carlo Perrier and Emilio Segrè. They examined a molybdenum foil made radioactive in Ernest Lawrence’s cyclotron and showed that it contained the long-sought element 43. Its name comes from the Greek technētos, meaning “artificial.”
The discovery filled a conspicuous gap in Dmitri Mendeleev’s periodic table. Technetium is the lightest element whose isotopes are all radioactive, although tiny natural traces can form through uranium fission and other nuclear processes. The statement that it was “artificially produced” refers to its discovery and predominant production, not to the absolute absence of natural technetium.
Technetium-99m, a short-lived radioactive nuclear isomer, is especially important in medicine. It emits detectable gamma rays and is used in millions of diagnostic imaging procedures, including bone and organ scans.