Short answers, pulled from the story.
Scientists Glenn T. Seaborg, Leon O. Morgan, Ralph A. James, and Albert Ghiorso discovered americium in the autumn of 1944 at the University of Chicago and the University of California, Berkeley. They used a 60-inch cyclotron to bombard plutonium-239 with neutrons to create the element. The discovery was officially announced after the team accidentally leaked the existence of elements 95 and 96 on the children's radio show Quiz Kids.
A typical smoke detector contains 1 microcurie of americium, which equals approximately 0.29 micrograms. This tiny amount of americium-241 dioxide is sufficient to ionize air and detect smoke particles. The isotope has a half-life of 432.2 years, ensuring the source remains effective for decades.
The isotope americium-242m has a half-life of 141 years and possesses the largest cross-section for absorbing thermal neutrons of any known isotope. Scientists propose using this isotope as fuel for compact nuclear reactors and propulsion systems for space ships. The European Space Agency is considering americium for space probes to address waning stockpiles of plutonium-238.
David Hahn, known as the Radioactive Boy Scout, was a 17-year-old who attempted to build a breeder nuclear reactor in 1994. He extracted americium from approximately 100 smoke detectors to create his own nuclear device. His project attracted the attention of the FBI and the Environmental Protection Agency, highlighting the risks of amateur nuclear experimentation.
Americium exhibits oxidation states ranging from +2 to +7, with +3 being the most stable state. The element forms insoluble salts such as fluoride, oxalate, and hydroxide in the +3 state. Americium metal has a density of 12 grams per cubic centimeter and changes crystal structure from hexagonal to face-centered cubic under extreme conditions.
Metamictization is a process where americium damages its own crystal structure by emitting alpha particles that strike surrounding atoms. This self-irradiation causes electrical resistivity to increase over time, rising from 2 microohm-centimeters to 10 microohm-centimeters after 40 hours. The effect saturates at about 16 microohm-centimeters after 140 hours and makes determining properties like the melting point uncertain.