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About Americium

Americium Bohr

Americium, a transuranic radioelement with a silvery white appearance and a density similar to lead, was discovered in 1944 at the Argonne National Laboratory by a team of scientists led by Glenn T. Seaborg. It was later synthesized at the University of California, Berkeley. The process of isolating americium from curium was so arduous that the researchers had taken to calling the elusive element "pandemonium". Americium occupies the spot below europium on the very last row of the periodic table, and was given its name as a result as of this association with the other element named after a continent.

Americium is the only synthetic element that has found a common consumer use: as the ionization source in commercial and residential smoke detectors. Additionally, americium is used as neutron source in neutron probes and neutron radiography and as a portable source of gamma rays and alpha particles in medical, scientific, and industrial applications. Americium is also a starting material for the production of other synthetic elements. Though americium is produced fairly routinely in nuclear reactors, the complexity of the separation procedures necessary to isolate it from other elements ensures that the supply of the pure element remains low, and the material remains quite expensive.

Americium Properties

Americium Bohr ModleAmericium is a Block F, Group 3, Period 7 element. The number of electrons in each of Americium's shells is 2, 8, 18, 32, 25, 8, 2 and its electron configuration is [Rn] 5f7 7s2. The americium atom has a radius of 173.pm and its Van der Waals radius is 244.pm. In its elemental form, CAS 7440-35-9, americium has a silvery white appearance. Americium was discovered by Glenn T. Seaborg, Ralph A. James, Stanley G. Thompson and Albert Ghiorso in 1944. It was the fourth synthetic transuranic element to be discovered and was named after the continent of North America.

Americium is artificially produced in small quantities for research purposes and use in smoke detectors. Due to its radioactivity, americium is harmful. Americium information, including properties, research, applications and other useful facts are discussed below. Scientific facts such as the atomic structure, ionization energy, abundance on Earth, conductivity and thermal properties are included.

Symbol: Am
Atomic Number: 95
Atomic Weight: 243
Element Category: Actinide
Group, Period, Block: n/a, 7, f
Color: silvery white
Other Names: Americio
Melting Point: 1176 °C, 2148.8 °F, 1449.15 K
Boiling Point: 2011 °C, 3651.8 °F, 2284.15 K
Density: 13670 kg·m3
Liquid Density @ Melting Point: N/A
Density @ 20°C: 13.67 g/cm3
Density of Solid: 13780 kg·m3
Specific Heat: N/A
Superconductivity Temperature: 0.6 [or -272.5 °C (-458.5 °F)] K
Triple Point: N/A
Critical Point: N/A
Heat of Fusion (kJ·mol-1): 14.4
Heat of Vaporization (kJ·mol-1): 238.5
Heat of Atomization (kJ·mol-1): 266
Thermal Conductivity: 10 W·m-1·K-1
Thermal Expansion: N/A
Electrical Resistivity: 0.69 µΩ·m
Tensile Strength: N/A
Molar Heat Capacity: 62.7 J·mol-1·K-1
Young's Modulus: N/A
Shear Modulus: N/A
Bulk Modulus: N/A
Poisson Ratio: N/A
Mohs Hardness: N/A
Vickers Hardness: N/A
Brinell Hardness: N/A
Speed of Sound: N/A
Pauling Electronegativity: 1.3
Sanderson Electronegativity: N/A
Allred Rochow Electronegativity: 1.2
Mulliken-Jaffe Electronegativity: N/A
Allen Electronegativity: N/A
Pauling Electropositivity: 2.7
Reflectivity (%): N/A
Refractive Index: N/A
Electrons: 95
Protons: 95
Neutrons: 148
Electron Configuration: [Rn] 5f7 7s2
Atomic Radius: 173 pm
Atomic Radius,
non-bonded (Å):
2.44
Covalent Radius: 180±6 pm
Covalent Radius (Å): 1.73
Van der Waals Radius: 244 pm
Oxidation States: 6, 5, 4, 3, 0
Phase: Solid 
Crystal Structure: hexagonal
Magnetic Ordering: paramagnetic
Electron Affinity (kJ·mol-1) Unknown
1st Ionization Energy: 578 kJ·mol-1
2nd Ionization Energy: N/A
3rd Ionization Energy: N/A
CAS Number: 7440-35-9
EC Number: N/A
MDL Number: N/A
Beilstein Number: N/A
SMILES Identifier: [Am]
InChI Identifier: InChI=1S/Am
InChI Key: LXQXZNRPTYVCNG-UHFFFAOYSA-N
PubChem CID: 23966
ChemSpider ID: 22405
Earth - Total: N/A
Mercury - Total: N/A
Venus - Total: N/A
Earth - Seawater (Oceans), ppb by weight: N/A
Earth - Seawater (Oceans), ppb by atoms: N/A
Earth -  Crust (Crustal Rocks), ppb by weight: N/A
Earth -  Crust (Crustal Rocks), ppb by atoms: N/A
Sun - Total, ppb by weight: N/A
Sun - Total, ppb by atoms: N/A
Stream, ppb by weight: N/A
Stream, ppb by atoms: N/A
Meterorite (Carbonaceous), ppb by weight: N/A
Meterorite (Carbonaceous), ppb by atoms: N/A
Typical Human Body, ppb by weight: N/A
Typical Human Body, ppb by atom: N/A
Universe, ppb by weight: N/A
Universe, ppb by atom: N/A
Discovered By: Glenn T. Seaborg, Ralph A. James, Leon O. Morgan, Albert Ghiorso
Discovery Date: 1944
First Isolation: N/A

Americium Isotopes

Americium is an artificial element. It has no stable isotopes.

Nuclide Isotopic Mass Half-Life Mode of Decay Nuclear Spin Magnetic Moment Binding Energy (MeV) Natural Abundance
(% by atom)
231Am 231.04556(32)# 30# s β+ to 231Pu; α to 227Np N/A N/A 1747.71301 -
232Am 232.04659(32)# 79(2) s β+ to 232Pu; α to 228Np N/A N/A 1754.824951 -
233Am 233.04635(11)# 3.2(8) min β+ to 233Pu; α to 229Np; SF N/A N/A 1763.0059813 -
234Am 234.04781(22)# 2.32(8) min β+ to 234Pu; α to 230Np; SF N/A N/A 1769.845947 -
235Am 235.04795(13)# 9.9(5) min β+ to 235Pu; α to 231Np 5/2-# N/A 1777.697998 -
236Am 236.04958(11)# 3.6(1) min β+ to 236Pu; α to 232Np N/A N/A 1784.334961 -
237Am 237.05000(6)# 73.0(10) min EC to 237Pu; α to 233Np 5/2(-) N/A 1792.032471 -
238Am 238.05198(5) 98(2) min EC to 238Pu; α to 234Np 1+ N/A 1798.234253 -
239Am 239.0530245(26) 11.9(1) h EC to 239Pu; α to 235Np (5/2)- N/A 1805.336182 -
240Am 240.055300(15) 50.8(3) h EC to 240Pu; α to 236Np (3-) N/A 1811.293579 -
241Am 241.0568291(20) 432.2(7) a α to 237Np; SF 5/2- 1.61 1817.935059 -
242Am 242.0595492(20) 16.02(2) h EC to 242Pu; β- to 242Cm 1- 0.388 1823.472534 -
243Am 243.0613811(25) 7,370(40) a α to 239Np; SF 5/2- 1.61 1829.8396 -
244Am 244.0642848(22) 10.1(1) h β- to 244Cm (6-)# N/A 1835.203247 -
245Am 245.066452(4) 2.05(1) h β- to 245Cm (5/2)+ N/A 1841.25708 -
246Am 246.069775(20) 39(3) min β- to 246Cm (7-) N/A 1846.23291 -
247Am 247.07209(11)# 23.0(13) min β- to 247Cm (5/2)# N/A 1852.145996 -
248Am 248.07575(22)# 3# min β- to 248Cm N/A N/A 1856.807983 -
249Am 249.07848(32)# 1# min β- to 249Cm N/A N/A 1862.332031 -
Americium Elemental Symbol

Recent Research & Development for Americium

  • New Insight into Self-Irradiation Effects on Local and Long-Range Structure of Uranium–Americium Mixed Oxides (through XAS and XRD). Florent Lebreton, Philippe M. Martin, Denis Horlait, René Bès, Andreas C. Scheinost, Andre Rossberg, Thibaud Delahaye, and Philippe Blanchart. Inorg. Chem.: August 27, 2014
  • Solution Speciation of Plutonium and Americium at an Australian Legacy Radioactive Waste Disposal Site. Atsushi Ikeda-Ohno, Jennifer J. Harrison, Sangeeth Thiruvoth, Kerry Wilsher, Henri K. Y. Wong, Mathew P. Johansen, T. David Waite, and Timothy E. Payne. Environ. Sci. Technol.: August 15, 2014
  • Aqueous Complexes for Efficient Size-based Separation of Americium from Curium. Mark P. Jensen, Renato Chiarizia, Ilya A. Shkrob, Joseph S. Ulicki, Brian D. Spindler, Daniel J. Murphy, Mahmun Hossain, Adrián Roca-Sabio, Carlos Platas-Iglesias, Andrés de Blas, and Teresa Rodríguez-Blas. Inorg. Chem.: June 3, 2014
  • Americium(III) Capture Using Phosphonic Acid-Functionalized Silicas with Different Mesoporous Morphologies: Adsorption Behavior Study and Mechanism Investigation by EXAFS/XPS. Wen Zhang, Xihong He, Gang Ye, Rong Yi, and Jing Chen. Environ. Sci. Technol.: May 19, 2014
  • XRD Monitoring of α Self-Irradiation in Uranium–Americium Mixed Oxides. Denis Horlait, Florent Lebreton, Pascal Roussel, and Thibaud Delahaye. Inorg. Chem.: November 22, 2013
  • Role of Cation Interactions in the Reduction Process in Plutonium–Americium Mixed Oxides. Renaud C. Belin, Philippe M. Martin, Jacques Lechelle, Muriel Reynaud, and Andreas C. Scheinost. Inorg. Chem.: February 26, 2013
  • Charge Distribution and Local Structure of Americium-Bearing Thorium Oxide Solid Solutions. U. Carvajal-Nunez, D. Prieur, T. Vitova, and J. Somers. Inorg. Chem.: October 16, 2012
  • Periodic Trends in Lanthanide and Actinide Phosphonates: Discontinuity between Plutonium and Americium. Juan Diwu, Daniel J. Grant, Shuao Wang, Laura Gagliardi, and Thomas E. Albrecht-Schmitt. Inorg. Chem.: June 5, 2012
  • Local Structure and Charge Distribution in Mixed Uranium–Americium Oxides: Effects of Oxygen Potential and Am Content. Damien Prieur, Philippe M. Martin, Aurélien Jankowiak, Elisabeth Gavilan, Andreas C. Scheinost, Nathalie Herlet, Philippe Dehaudt, and Philippe Blanchart. Inorg. Chem.: November 16, 2011