Americium
In late autumn 1944, a team at the University of California, Berkeley, used a massive 60-inch cyclotron to create a new element. Glenn T. Seaborg, Leon O. Morgan, Ralph A. James, and Albert Ghiorso worked together in this laboratory setting. They produced americium from plutonium-239 nitrate coated on platinum foil. The process involved evaporation and calcination into plutonium dioxide before irradiation. This work occurred under the umbrella of the Manhattan Project during World War II. The results remained classified until November 1945 when they were finally released to the public. Seaborg accidentally leaked details about the discovery five days before an official American Chemical Society meeting. He did so while appearing on a children's radio show called Quiz Kids. The initial samples weighed only a few micrograms and were barely visible to the naked eye. These tiny amounts glowed with intense radioactivity that scientists could detect but not see directly. The secrecy surrounding these early experiments meant that the world knew nothing about this transuranic element for over a year after its creation.
The chemical isolation of americium required a complex multi-step procedure involving multiple reagents. Plutonium-239 nitrate solution was first evaporated onto a small platinum foil area of roughly 0.5 square centimeters. After cyclotron irradiation, workers dissolved the coating using concentrated nitric acid. They then precipitated the material as hydroxide using aqueous ammonia. Further separation relied on ion exchange techniques to isolate specific isotopes from curium. The difficulty of separating these two elements led the Berkeley group to nickname them pandemonium and delirium respectively. A typical modern process dissolves spent reactor fuel in nitric acid to remove bulk uranium and plutonium via PUREX extraction. Lanthanides and remaining actinides separate from the residue using diamide-based extraction methods. Americium compounds get selectively extracted through chromatographic and centrifugation techniques. One proposed reagent involves bis-triazinyl bipyridine complexes which show high selectivity for americium. Separating americium from curium often requires treating their hydroxide slurry with ozone at elevated temperatures. This oxidation step converts americium into soluble Am(IV) complexes while leaving curium unchanged. Metallic americium finally emerges from reduction reactions using barium metal inside vacuum chambers made of tantalum and tungsten.
Freshly prepared americium displays a silvery-white metallic lustre that slowly tarnishes upon exposure to air. Its density measures 12 grams per cubic centimeter, placing it between lighter lanthanides and heavier actinides. The melting point reaches 1173 degrees Celsius, significantly higher than plutonium but lower than curium. At ambient conditions, the element exists as alpha-americium with hexagonal crystal symmetry. This structure features double-hexagonal close packing with layer sequences ABAC. Compressing the material to 5 gigapascals transforms it into beta modification with face-centered cubic symmetry. Further compression up to 23 gigapascels creates an orthorhombic gamma phase similar to uranium. Self-irradiation damage occurs naturally within the crystal lattice due to alpha particle emission over time. Electrical resistivity increases gradually in fresh samples from liquid helium temperatures to room temperature values. Low temperature measurements show mobility of radiation defects remains relatively low compared to other elements. Heating samples back to room temperature restores their original resistivity properties after prolonged storage at cryogenic levels. The thermal expansion coefficient varies slightly along different axes of the hexagonal unit cell. Paramagnetic behavior persists across wide temperature ranges unlike its neighbor curium which shows antiferromagnetic transitions.
Americium readily reacts with oxygen and dissolves easily in aqueous acids to form various salts. The most stable oxidation state for this element is plus three found in solutions. Several other states ranging from plus two to plus seven have been identified through optical absorption spectra. Trivalent americium forms insoluble fluoride, oxalate, iodate, hydroxide, phosphate and other common salts. Compounds in higher oxidation states act as strong oxidizing agents comparable to permanganate ions. Americium dioxide serves as the main solid form used in nearly all practical applications today. Halides exist for oxidation states plus two, plus three, and plus four where trivalent remains dominant. Black halides like AmCl2, AmBr2, and AmI2 result from reduction reactions with sodium amalgam. These black compounds oxidize rapidly in water releasing hydrogen gas while reverting to the trivalent state. Oxidation state plus five first appeared in 1951 within acidic aqueous solutions. Pentavalent ions prove unstable regarding disproportionation into lower or higher states. Oxyhalides such as AmVO2X and AmIVOX2 form when reacting halides with oxygen or antimony trioxide. Chalcogenides include sulfide AmS2, selenides AmSe2, and tellurides Am2Te3 among others. Silicides and borides demonstrate diverse crystal symmetries including orthorhombic and tetragonal structures. Organoamericium compounds like amerocene feature cyclooctatetraene ligands surrounding the central metal atom.
Household smoke detectors utilize americium-241 as their primary source of ionizing radiation. A typical new detector contains approximately one microcurie or 0.29 micrograms of this isotope. The amount declines slowly over decades as it decays into neptunium-237 which has a much longer half-life. After nineteen years, about three percent of the original americium converts to neptunium. By thirty-two years, that figure reaches roughly five percent. Alpha particles pass through an air-filled ionization chamber between two electrodes creating a constant current. Any smoke entering the chamber absorbs these alpha particles reducing ionization levels. This drop in current triggers the alarm system immediately. Compared to optical alternatives, ionization detectors remain cheaper while detecting smaller particles effectively. They do suffer from higher rates of false alarms compared to other technologies. The isotope emits five times more alpha particles than radium alternatives with minimal harmful gamma radiation. Most americium enters landfills when people discard old smoke detectors despite relaxed disposal rules. One seventeen-year-old named David Hahn extracted material from about one hundred detectors attempting to build a breeder reactor. Chemical operations technician Harold McCluskey suffered exposure to five hundred times the occupational standard during a lab explosion.
The isomer 242mAm possesses a half-life of 141 years and exhibits massive neutron absorption cross sections. Its critical mass for a bare sphere measures approximately nine to fourteen kilograms depending on reflectors. Adding metal or water reflectors could reduce this requirement down to three to five kilograms. Such small masses make portable nuclear weapons theoretically possible though none exist currently due to scarcity. Very compact ten-kilowatt high-flux reactors might use as little as twenty grams of this specific isomer. These low-power units would serve safely as neutron sources for hospital radiation therapy treatments. Spacecraft propulsion systems could rely on fission products directly propelling ships or heating thrusting gases. A single 3.2 kilogram charge of 242mAm could provide roughly 140 kilowatts over eighty days. Researchers at the UK National Nuclear Laboratory demonstrated heat generation capabilities in 2019 by lighting a bulb. This technology promises missions lasting up to four hundred years into interstellar space where solar panels fail. The European Space Agency considers using americium-241 for future probes despite lower power yields than plutonium-238. Neutron sources combine americium oxide with beryllium to produce efficient radiation for soil moisture measurement. Well logging applications utilize these sources alongside tomography and radiochemical investigations globally.
Continue Browsing
Common questions
Who discovered americium and when was it created?
Glenn T. Seaborg, Leon O. Morgan, Ralph A. James, and Albert Ghiorso created americium in late autumn 1944 at the University of California, Berkeley. The results remained classified until November 1945 when they were finally released to the public.
How did scientists isolate americium from plutonium-239 nitrate?
Scientists produced americium by evaporating plutonium-239 nitrate onto platinum foil before irradiating it with a 60-inch cyclotron. They dissolved the coating using concentrated nitric acid and precipitated the material as hydroxide using aqueous ammonia for further separation via ion exchange techniques.
What are the physical properties of metallic americium?
Freshly prepared americium displays a silvery-white metallic lustre that slowly tarnishes upon exposure to air. Its density measures 12 grams per cubic centimeter and its melting point reaches 1173 degrees Celsius.
Why is americium used in household smoke detectors?
Household smoke detectors utilize americium-241 as their primary source of ionizing radiation because alpha particles pass through an air-filled ionization chamber between two electrodes creating a constant current. Any smoke entering the chamber absorbs these alpha particles reducing ionization levels which triggers the alarm system immediately.
What potential uses exist for the isomer 242mAm?
The isomer 242mAm possesses a half-life of 141 years and exhibits massive neutron absorption cross sections suitable for spacecraft propulsion systems or hospital radiation therapy treatments. A single 3.2 kilogram charge of 242mAm could provide roughly 140 kilowatts over eighty days according to researchers at the UK National Nuclear Laboratory who demonstrated heat generation capabilities in 2019.