Americium is a radioactive metallic element with atomic number 95 and element symbol Am. It's the only synthetic element encountered in everyday life, in minute quantities in ionization-type smoke detectors. Americium was first synthesized and identified in 1944 by Glenn T. Seaborg, Ralph James, L Morgan, and Albert Ghiorso at the University of California, Berkeley as part of the Manhattan Project. The element was produced using a 60-inch cyclotron. Americium is a shiny silver radioactive metal. All isotopes of this element are radioactive. The isotope with the longest half-life is americium-243, which has a half-life of 7370 years. The most common isotopes are americium-241, with a half-life of 432.7 years, and americium-243. Americium-242 is also known, with a half-life of 141 years. In total, 19 isotopes and 8 nuclear isomers have been characterized. The isotopes variously undergo alpha, beta, and gamma decay. EPA Facts AboutAmericium-241EPA Facts About Americium-241 July 2002 What is americium-241? Americium is a man-made radioactive metal that exists as a solid under normal conditions. Americium is produced when plutonium absorbs neutrons in nuclear reactors and nuclear weapons tests. Americium occurs in several forms called isotopes. The most common isotope is americium-241. Americium when blended with beryllium is used as a neutron source in the testing of machinery and in thickness gauges in the glass industry. Americium also is used as a radiation source in medical diagnostic devices and in research. Possible uses are in medicine where gamma emission of Am-241 has allowed the deter-mination of mineral content of bones, lipid content of soft tissues, and body composition. Americium is commonly used in minute amounts in smoke detectors as an ionization source. However this isotope is extremely expensive to produce in usable quantities. There is no known biological role of americium in living organisms. It's generally considered toxic because of its radioactivity.