Americium

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Americium

Americium is a synthetic element

Synthetic element

In chemistry, the chemical elements labeled as synthetic are too unstable to be found naturally on Earth. These synthetic elements possess half-lifes so short, relative to the age of the Earth, that any atoms of these elements that may have existed when the Earth formed have long since decayed away....
that has the symbol Am and atomic number

Atomic number

In chemistry and physics, the atomic number is the number of protons found in the atomic nucleus of an atom. It is conventionally represented by the symbol Z....
95. A radioactive

Radioactive decay

Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
lic element, americium is an actinide

Actinide

According to IUPAC nomenclature, the actinoid series encompasses the 15 chemical elements that lie between actinium and lawrencium included on the periodic table, with atomic numbers 89 - 103....
that was obtained in 1944 by Glenn T. Seaborg

Glenn T. Seaborg

Glenn Theodore Seaborg was an American scientist who won the 1951 Nobel Prize in Chemistry for "discoveries in the chemistry of the transuranic element," contributed to the discovery and isolation of ten elements, developed the actinide concept and was the first to propose the actinide series which led to the current arrangement of the Perio...
who was bombarding plutonium

Plutonium

Plutonium is a rare transuranic radioactive chemical element. It is an actinide metal of silvery-white appearance that tarnishes when exposed to air, forming a dull coating when plutonium oxide....
with neutron

Neutron

The neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton.Neutrons are usually found in atomic nucleus....
s and was the fourth transuranic element to be discovered. It was named for the Americas

Americas

The Americas are the region of the Western hemisphere that consists of the continents of North America and South America with their associated islands and regions....
, by analogy with europium

Europium

Europium is a chemical element with the symbol Eu and atomic number 63. It was named after the continent Europe.Characteristics ...
. Americium is widely used in commercial ionization-chamber smoke detectors as well as in neutron sources and industrial gauges.

Pure americium has a silvery and white luster.

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Encyclopedia

Americium is a synthetic element

Synthetic element

Atomic number

In chemistry and physics, the atomic number is the number of protons found in the atomic nucleus of an atom. It is conventionally represented by the symbol Z....
95. A radioactive

Radioactive decay

Metal

Actinide

Glenn T. Seaborg

Plutonium

Neutron

Americas

The Americas are the region of the Western hemisphere that consists of the continents of North America and South America with their associated islands and regions....
, by analogy with europium

Europium

Properties

Pure americium has a silvery and white luster. At room temperature

Room temperature

Room temperature is a common term to denote a certain temperature within enclosed space at which humans are accustomed.Room temperature is thus often indicated by general human comfort, with the common range of 10celsius to 23?C , though climate may acclimatize people to higher or lower temperatures....
s it slowly tarnishes in dry air. It is more silvery than plutonium

Plutonium

Neptunium

Uranium

Uranium is a silvery-gray metallic chemical element in the actinide series of the periodic table that has the chemical symbol U and atomic number 92....
. Alpha emission from ²⁴¹Am is approximately three times that of radium

Radium

Radium is a radioactive chemical element which has the symbol Ra and atomic number 88. Its appearance is almost pure white, but it readily oxidizes on exposure to air, turning black....
. Gram

Gram

The gram , ; symbol g, is a Physical unit of mass.Originally defined as "the absolute weight of a volume of pure water equal to the cube of the hundredth part of a metre, and at the temperature of melting ice" , a gram is now defined as one one-thousandth of the SI base unit, the kilogram, or Scientific notation kg, which itself is...
quantities of ²⁴¹Am emits alpha particles and low energy gamma ray

Gamma ray

Gamma rays are a form of electromagnetic radiation produced by atom particle interactions, such as electron-positron annihilation or radioactive decay....
s (60 keV, giving a dose at 1 metre of 0.0011 mSv/yr).

Americium is also fissile

Fissile

In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission.All known fissile materials are capable of sustaining a chain reaction in which either thermal or slow neutrons or fast neutrons predominate....
; the critical mass for an unreflected sphere of ²⁴¹Am is approximately 60 kilograms. It is unlikely that Americium would be used as a weapons material, as its minimum critical mass is considerably larger than that of more readily obtained plutonium

Plutonium

Uranium

Uranium is a silvery-gray metallic chemical element in the actinide series of the periodic table that has the chemical symbol U and atomic number 92....
isotopes.

Applications

Americium can be produced in kilogram

Kilogram

The kilogram or kilogrammeThe spelling kilogram is used by the International Committee for Weights and Measures and the U.S....
amounts and has some uses, mostly involving ²⁴¹Am since it is easiest to produce relatively pure samples of this isotope. Americium is the only synthetic element to have found its way into the household, where one common type of smoke detector

Smoke detector

A smoke detector is a device that detects smoke and issues a signal to a fire alarm system, or issues a local audible and/or visual alarm from the detector itself....
contains a tiny amount (about 0.2 microgram

Microgram

In the metric system, a microgram is 1/1,000,000 of a gram , or 1/1000 of a milligram, is one of the smallest units of weight/mass commonly used....
) of ²⁴¹Am as a source of ionizing radiation

Ionizing radiation

Ionizing radiation consists of subatomic particle radiation or electromagnetic radiation that are energetic enough to detach electrons from atoms or molecules, ionize them....
. This amount emits about 1 microcurie of nuclear radiation when new, with the amount declining slowly as the americium decays into neptunium

Neptunium

Neptunium is a chemical element with the symbol Np and atomic number 93. A radioactivity metallic element, neptunium is the first transuranic element and belongs to the actinide series....
, a different transuranic element, with a much longer half-life (about 2.14 million years). With its half-life of 432 years, the americium-241 in a smoke detector includes about 5% neptunium after 22 years, and about 10% after 43 years. After the 432-year americium-241 half-life, a smoke detector's original americium would, by definition, be more than half neptunium.

²⁴¹Am has been used as a portable source of both gamma rays and alpha particles for a number of medical and industrial uses. Gamma ray emissions from ²⁴¹Am can be used for indirect analysis of materials radiography

Radiography

Radiography is the use of X-rays to view unseen or hard-to-image objects. The main diagnostic purposes of X-rays are to see inside one's body, most commonly the bones which can be viewed at an optimum resolution ....
and for quality control in manufacturing [fixed gauges]. For example, the element has been employed to gauge glass

Glass

Glass generally refers to a Hardness, brittle, transparency amorphous solid, such as that used for windows, many Glass Bottles, or eyewear, including, but not limited to, soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovite , or aluminium oxynitride....
thickness to help create flat glass. ²⁴¹Am gamma rays were also used to provide passive diagnosis of thyroid function. This medical application is obsolete. ²⁴¹Am can be combined with lighter elements (e.g., beryllium or lithium) to become a neutron emitter. This application has found uses in neutron radiography as well as a neutron emitting radioactive source. The most widespread use of ²⁴¹AmBe neutron sources is found in moisture/density gauges used for quality control in highway construction. ²⁴¹Am neutron sources are also critical for well logging applications. It has also been cited for use as an advanced nuclear rocket propulsion fuel. This isotope is, however, extremely expensive to produce in usable quantities.

²⁴¹Am has recently been suggested for use as a denaturing agent in plutonium

Plutonium

History

Americium was first isolated by Glenn T. Seaborg

Glenn T. Seaborg

Albert Ghiorso

Albert Ghiorso is an American nuclear scientist who helped discover numerous chemical elements on the periodic table....
in late 1944 at the wartime Metallurgical Laboratory at the University of Chicago

University of Chicago

The University of Chicago is a private university located principally in the Hyde Park, Chicago neighborhood of Chicago. Although an older university by the same name existed prior to its founding, the modern University of Chicago credits its founding to the oil magnate John D....
(now known as Argonne National Laboratory

Argonne National Laboratory

Argonne National Laboratory is one of the United States Department of Energy's oldest and largest science and engineering research United States Department of Energy National Labs and is the largest in size in the Midwest ....
). The team created the isotope

Isotope

Isotopes are any of the different types of atoms of the same chemical element, each having a different atomic mass . Isotopes of an element have atomic nucleus with the same number of protons but different numbers of neutron....
²⁴¹Am by subjecting ²³⁹Pu

Plutonium

Neutron capture

Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus....
reactions in a nuclear reactor

Nuclear reactor

A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate, as opposed to a nuclear bomb, in which the chain reaction occurs in a fraction of a second and is uncontrolled causing an explosion....
. This created ²⁴⁰Pu and then ²⁴¹Pu which in turn decayed into ²⁴¹Am via beta decay

Beta decay

In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus , while in the case of a positron emission as beta plus ....
.

Seaborg was granted a patent for "Element 95 and Method of Producing Said Element," whose unusually terse claim number 1 reads simply, "Element 95." The discovery of americium and curium

Curium

Isotopes

Eighteen radioisotopes of americium have been characterized, with the most stable being ²⁴³Am with a half-life

Half-life

The half-life of a quantity whose value decreases with time is the interval required for the quantity to decay to half of its initial value. The concept originated in describing how long it takes atoms to undergo radioactive decay but also applies in a wide variety of other situations....
of 7370 years, and ²⁴¹Am with a half-life of 432.2 years. All of the remaining radioactive

Radioactive decay

Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide....
isotopes have half-lives that are less than 51 hours, and the majority of these have half-lives that are less than 100 minutes. This element also has 8 meta states, with the most stable being ^242mAm (t_½ 141 years). The isotopes of americium range in atomic weight

Atomic weight

Atomic weight is a Dimensionless quantity physical quantity, the ratio of the average mass of atoms of an chemical element to 1/12 of the mass of an atom of carbon-12....
from 231.046 u

Atomic mass unit

The unified atomic mass unit , or dalton or, sometimes, universal mass unit, is a Units of measurement of mass used to express atomic weight and molecular masses....
(²³¹Am) to 249.078 u (²⁴⁹Am).

Chemistry

In aqueous systems the most common oxidation state is +3. It is very much harder to oxidize Am(III) to Am(IV) than it is to oxidise Pu(III) to Pu(IV).

Currently the solvent extraction chemistry of americium is important as in several areas of the world scientists are working on reducing the medium term radiotoxicity

Ionizing radiation

Ionizing radiation consists of subatomic particle radiation or electromagnetic radiation that are energetic enough to detach electrons from atoms or molecules, ionize them....
of the waste from the reprocessing of used nuclear fuel

Nuclear fuel

Nuclear fuel is any material that can be consumed to derive nuclear energy, by analogy to chemical fuel that is Combustioned to derive energy....
.

See liquid-liquid extraction

Liquid-liquid extraction

Liquid-liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds based on their relative solubility in two different miscible liquids, usually Water and an solvent....
for some examples of the solvent extraction of americium.

Americium, unlike uranium, does not readily form a dioxide americyl core (AmO₂). This is because americium is very hard to oxidise above the +3 oxidation state when it is in an aqueous solution. In the environment, this americyl core could complex with carbonate as well as other oxygen moieties (OH^-, NO₂^-, NO₃^-, and SO₄^-2) to form charged complexes which tend to be readily mobile with low affinities to soil.

AmO₂(OH)⁺¹
AmO₂(OH)₂⁺²
AmO₂CO₃⁺¹
AmO₂(CO₃)₂^-1
AmO₂(CO₃)₃^-3

A large amount of work has been done on the solvent extraction of americium, as it is the case that americium and the other transplutonium elements are responsible for the majority of the long lived radiotoxicity of spent nuclear fuel

Spent nuclear fuel

File:Spent nuclear fuel hanford.jpgSpent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor to the point where it is no longer useful in sustaining a nuclear reaction....
. It is thought that by removal of the americium and curium

Curium

Curium is a synthetic element with the symbol Cm and atomic number 96. A Radioactive decay metallic transuranic element of the actinide series, curium is produced by bombarding plutonium with alpha particles and was named for Maria Sklodowska-Curie and her husband Pierre Curie....
that the used fuel will only need to be isolated from man and his environment for a shorter time than that required for the isolation of untreated used fuel. One recent EU funded project on this topic was known by the codename "EUROPART". Within this project triazines and other compounds were studied as potential extraction agents.

Americium

Properties

Applications

History

Isotopes

Chemistry

Further reading

External links