Taking its name from the Greek word "technetos," meaning artificial, technetium [Tc43] was the first synthetically produced element. In 1937, researchers Carlo Perrier and Emilio Segre discovered technetium after bombarding a sample of molybdenum with deuterium nuclei. Doctors and medical researchers use minute amounts of this silvery-grey metal as a radioactive tracer to detect certain illnesses and to monitor body functions. Engineers use technetium to calibrate machinery, and small concentrations of technetium oxide can protect steel and iron from corrosion.
Uranium, with an atomic number of 92, is the heaviest known naturally occurring element. Neptunium [Np93] was the first synthesized transuranium (after uranium) element. Working at the University of California's Berkeley Radiation Laboratory, Edwin McMillan and Philip H. Abelson produced Neptunium by bombarding uranium with neutrons. They named the new element Neptunium after the planet Neptune, the next planet after uranium's namesake Uranus.
First produced in 1940 by a research team including Glenn Seaborg, Edwin McMillan, Joseph Kennedy and Arthur Wahl, plutonium [Pu94] takes its name from the planet Pluto, following in line with uranium and neptunium. Researchers discovered that bombarding the heavy, unstable element with slow neutrons caused it to break down in a fission chain reaction, releasing incredible amounts of energy. Nuclear power plants us a controlled plutonium fission reaction to produce electricity, and an uncontrolled fission chain reaction releases the destructive force of the atomic bomb.
Working in 1944 at the University of Chicago, the researchers Seaborg, James and Morgan initially referred to americium [Am95] as "pandemonium" due to the difficulties they experienced trying to isolate the new element. Ionization chamber smoke detectors contain small amounts of this silvery-white, highly radioactive metal in the form of americium dioxide. One gram of americium dioxide can produce over three million household smoke detectors.