Technetium

Element 43 was one of the remaining gaps in the periodic table. Technetium was briefly produced by bombarding molybdenum not with neutrons, but with deuterons because these charged particles could be greatly accelerated in a cyclotron. It is the simplest element with no stable isotopes to have been formed in the laboratory.
 Emilio Gino Segrè Italy 1937 Technetium

Element 43 was one of the remaining gaps in the periodic table. Technetium was briefly produced by bombarding molybdenum not with neutrons, but with deuterons because these charged particles could be greatly accelerated in a cyclotron. It is the simplest element with no stable isotopes to have been formed in the laboratory.