Americium is an actinoid metal and a heavy transuranic element. In its pure state, freshly prepared Americium is a lustrous silver-white metal; it tarnishes slowly on contact with air. Its atomic number is 95; its atomic symbol is Am. It has an atomic mass of 248, an atomic radius of 184 picometers, and a density of 13.69 grams per cubic centimetre. Like all transuranic elements, Americium is radioactive; its most stable isotope, Americium 243, decays with a half life of about 7370 years, and its most common isotope, Americium 241, has a half life of 432.2 years. Americium decays into Neptunium through emission of alpha radiation.
Americium is a synthetic element which does not occur naturally on Earth in detectable quantities; because it has a relatively short half life, any deposits which might have originally formed in the Earth’s crust would have decayed a long time ago. Americium is produced in large quantities in the lab by bombarding Plutonium with heavy neutron radiation. Americium is also a normal byproduct of atomic explosions and is sometimes produced in controlled nuclear reactions in power plants. Americium is highly radiocative, giving off intense low energy gamma radiation and about three times as much alpha radiation as radium; when handling Americium even in relatively minute quantities, precautions must be taken to ensure that no exposure to radiation or radioactive contamination occurs. Americium can be absorbed by the body and become concentrated in the bones; it is thus capable of causing cancer and radiation sickness. Americium it is one of the dangerous components of nuclear fallout and radioactive waste. Americium was discovered by Glenn Seaborg, Ralph James, Leon Morgan, and Albert Ghiorso in 1944 at the University of Chicago Metallurgical Laboratory. Its name, of course, refers to the Americas.
Despite its high radioactivity and the expense of producing it in usable quantities, Americium does have some common industrial uses. Combining Americium with lighter elements such as Beryllium creates a relatively benign neutron emitter. Minute amounts of Americium are used in smoke detectors, in guages used for quality control purposes in such applications as highway construction and glass manufacturing, and in neutron radiography. It has been used for medical diagnotic techniques, though it is now obsolete in this field. Americium, like many radioactive materials, can be used to create an atomic chain reaction; however, having a critical mass of about 60 kilograms, Americium is not as useful a fissile material as more common and cheaper materials such as Uranium and Plutonium and thus is not used to create nuclear weapons or nuclear reactors. Americium has been suggested as a high-power nuclear rocket fuel, and as an agent to stop people from making Plutonium fuel rods into nuclear weapons. However, for the most part, pure Americium is nothing but a laboratory curiosity.
Los Alamos National Laboratory