Americium

Americium, ₉₅Am

Americium
Pronunciation	/ˌæməˈrɪsiəm/ (listenⓘ) ​(AM-ə-RISS-ee-əm)
Appearance	silvery white
Mass number	[243]
Americium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Eu ↑ Am ↓ (Uqe) plutonium ← americium → curium
Atomic number (Z)	95
Group	f-block groups (no number)
Period	period 7
Block	f-block
Electron configuration	[Rn] 5f7 7s2
Electrons per shell	2, 8, 18, 32, 25, 8, 2
Physical properties
Phase at STP	solid
Melting point	1449 K ​(1176 °C, ​2149 °F)
Boiling point	2880 K ​(2607 °C, ​4725 °F) (calculated)
Density (near r.t.)	12 g/cm3
Heat of fusion	14.39 kJ/mol
Molar heat capacity	28[1] J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 1239 1356
Atomic properties
Oxidation states	+2, +3, +4, +5, +6, +7 (an amphoteric oxide)
Electronegativity	Pauling scale: 1.3
Ionization energies	1st: 578 kJ/mol
Atomic radius	empirical: 173 pm
Covalent radius	180±6 pm
Spectral lines of americium
Other properties
Natural occurrence	synthetic
Crystal structure	​double hexagonal close-packed (dhcp)
Thermal conductivity	10 W/(m⋅K)
Electrical resistivity	0.69 µΩ⋅m[1]
Magnetic ordering	paramagnetic
Molar magnetic susceptibility	+1000.0×10−6 cm3/mol[2]
CAS Number	7440-35-9
History
Naming	after the Americas
Discovery	Glenn T. Seaborg, Ralph A. James, Leon O. Morgan, Albert Ghiorso (1944)
Isotopes of americium v e
Main isotopes[3] Decay abun­dance half-life (t1/2) mode pro­duct 241Am synth 432.2 y α 237Np SF – 242m1Am synth 141 y IT 242Am α 238Np SF – 243Am synth 7350 y α 239Np SF –
Category: Americium view talk edit | references

Americium is a transuranic, radioactive chemical element with the symbol Am and the atomic number 95. In chemistry, it is placed in a group of metal elements named the actinides. Americium does not exist in nature and has to be made by chemists

Americium is silver in color, and is made by bombarding a plutonium target with neutrons.

It was the fourth transuranic element to be discovered. It was named for the Americas, like europium was named for Europe.^[4][5]

The longest half life of any type of americium is 7370 years.^[6]

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Americium is a synthetic element, so it must be made by people and is not found in nature. Most americium is made as a byproduct of nuclear reactors, and can be separated out during nuclear reprocessing.

The two most stable isotopes of americium are ²⁴¹Am and ²⁴³Am. They are made by beta decay of the same-weight plutonium isotopes, ²⁴¹Pu and ²⁴³Pu, which are made from neutron capture in thermal reactors.

Most americium is ²⁴¹Am. ²⁴¹Pu has a 14 year half-life and large fission cross section, so decaying to americium is rare in active reactors. Most ²⁴¹Am is found in spent nuclear fuel, where plutonium is more likely to decay than go through fission. ²⁴¹Am is also a byproduct of nuclear weapons production, which needs to separate ²⁴¹Pu from ²³⁹Pu to produce weapons-grade plutonium.

Americium is used in ionization-type smoke detectors. The level of radioactivity is not enough to cause cancer, and it cannot get through the smoke detector's plastic case, so it is safe to live in a place where smoke detectors with americium are used. This type of smoke detector is becoming obsolete, and is being replaced by optical smoke detectors, which have fewer false alarms and don't contain radioactive material.