Americium

Americium (Am)

Radioactive metallic transuranic element, belongs to the actinoids. Ten known isotopes. Am-243 is the most stable isotope, with a half-life of 7.95*10^3 years. Discovered by Glenn T. Seaborg and associates in 1945, it was obtained by bombarding Uranium-238 with alpha particles.
Atomic Number95
Atomic Weight243
Mass Number223
Group
Period7
Blockf
Protons95 p+
Neutrons128 n0
Electrons95 e-
Americium microscope.jpg Animated Bohr Model of Am (Americium) Enhanced Bohr Model of Am (Americium) Bohr Model: Am (Americium) Orbital Diagram of Am (Americium)

Properties

Atomic Radius
175 pm
Molar Volume
Covalent Radius
166 pm
Metallic Radius
Ionic Radius
121 pm
Crystal Radius
135 pm
Van der Waals Radius
244 pm
Density
Energy
Proton Affinity
Electron Affinity
Ionization Energy
Heat of Vaporization
238.5 kJ/mol
Heat of Fusion
Heat of Formation
284 kJ/mol
Electrons
Electron Shells2, 8, 18, 32, 25, 8, 2
Valence Electrons4
Electron Configuration[Rn] 5f7 7s2
Oxidation States2, 3, 4, 5, 6, 7
Electronegativity
Electrophilicity
Phases
PhaseSolid
Gas Phase
Boiling Point
Melting Point
1,449.15 K
Critical Pressure
Critical Temperature
Triple Point
Visual
Color
Silver
Appearancesilvery white
Refractive Index
Thermodynamic Properties
Thermal Conductivity
Thermal Expansion
Molar Heat Capacity
Specific Heat Capacity
Heat Capacity Ratio (Adiabatic Index)
Electrical Properties
Type
Electrical Conductivity
Electrical Resistivity
Superconducting Point
0.6 K
Magnetism
Typeparamagnetic
Magnetic Susceptibility (Mass)
0.0000000515 m³/Kg
Magnetic Susceptibility (Molar)
0.00000001251 m³/mol
Magnetic Susceptibility (Volume)
0.000704
Magnetic Ordering
Curie Point
Neel Point
Structure
Crystal StructureSimple Hexagonal ()
Lattice Constant
Lattice Anglesπ/2, π/2, 2 π/3
Mechanical Properties
Hardness
Bulk Modulus
Shear Modulus
Young Modulus
Poisson Ratio
Speed of Sound
Classification
CategoryActinides, Actinides
CAS Group
IUPAC Group
Glawe Number39
Mendeleev Number26
Pettifor Number42
Geochemical Class
Goldschmidt Classsynthetic
Other
Gas Basicity
Dipole Polarizability
131 ± 25 a₀
C6 Dispersion Coefficient
Allotropes
Neutron Cross Section
74
Neutron Mass Absorption
Quantum Numbers8S7/2
Space Group194 (P63/mmc)

Isotopes of Americium

Stable Isotopes0
Unstable Isotopes27
Radioactive Isotopes27

223Am

AbundanceRadioactive ☢️
Relative Atomic Mass
223.04584 ± 0.000322 Da
Mass Number223
G-Factor
Half Life
10 ± 9 ms
Spin9/2
Quadrupole Moment
Discovery Year2015
Parity-

223Am Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

224Am

AbundanceRadioactive ☢️
Relative Atomic Mass
224.046442 ± 0.000429 Da
Mass Number224
G-Factor
Half Life
Spin
Quadrupole Moment
Discovery Year
Parity

224Am Decay Modes
Decay ModeIntensity
α (α emission)%
SF (spontaneous fission)%

225Am

AbundanceRadioactive ☢️
Relative Atomic Mass
225.045508 ± 0.000429 Da
Mass Number225
G-Factor
Half Life
Spin9/2
Quadrupole Moment
Discovery Year
Parity-

225Am Decay Modes
Decay ModeIntensity
α (α emission)%
SF (spontaneous fission)%

226Am

AbundanceRadioactive ☢️
Relative Atomic Mass
226.04613 ± 0.000322 Da
Mass Number226
G-Factor
Half Life
Spin
Quadrupole Moment
Discovery Year
Parity

226Am Decay Modes
Decay ModeIntensity
α (α emission)%
SF (spontaneous fission)%

227Am

AbundanceRadioactive ☢️
Relative Atomic Mass
227.045282 ± 0.000215 Da
Mass Number227
G-Factor
Half Life
Spin9/2
Quadrupole Moment
Discovery Year
Parity-

227Am Decay Modes
Decay ModeIntensity
α (α emission)%
SF (spontaneous fission)%

228Am

AbundanceRadioactive ☢️
Relative Atomic Mass
228.046001 ± 0.000215 Da
Mass Number228
G-Factor
Half Life
Spin
Quadrupole Moment
Discovery Year
Parity

228Am Decay Modes
Decay ModeIntensity
α (α emission)%
SF (spontaneous fission)%

229Am

AbundanceRadioactive ☢️
Relative Atomic Mass
229.045282534 ± 0.000114169 Da
Mass Number229
G-Factor
Half Life
1.8 ± 1.5 s
Spin5/2
Quadrupole Moment
Discovery Year2015
Parity-

229Am Decay Modes
Decay ModeIntensity
α (α emission)100%
β+ (β+ decay; β+ = ϵ + e+)%

230Am

AbundanceRadioactive ☢️
Relative Atomic Mass
230.046025 ± 0.000153 Da
Mass Number230
G-Factor
Half Life
40 ± 9 s
Spin1
Quadrupole Moment
Discovery Year2003
Parity-

230Am Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
β+ SF (β+-delayed fission)30%

231Am

AbundanceRadioactive ☢️
Relative Atomic Mass
231.045529 ± 0.000322 Da
Mass Number231
G-Factor
Half Life
Spin5/2
Quadrupole Moment
Discovery Year
Parity-

231Am Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)%
α (α emission)%

232Am

AbundanceRadioactive ☢️
Relative Atomic Mass
232.046613 ± 0.000322 Da
Mass Number232
G-Factor
Half Life
1.31 ± 0.04 m
Spin1
Quadrupole Moment
Discovery Year1967
Parity-

232Am Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)97%
α (α emission)%
β+ SF (β+-delayed fission)0.069%

233Am

AbundanceRadioactive ☢️
Relative Atomic Mass
233.046468 ± 0.000123 Da
Mass Number233
G-Factor
Half Life
3.2 ± 0.8 m
Spin5/2
Quadrupole Moment
Discovery Year2000
Parity-

233Am Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)%
α (α emission)4.5%

234Am

AbundanceRadioactive ☢️
Relative Atomic Mass
234.047731 ± 0.000172 Da
Mass Number234
G-Factor
0
Half Life
2.32 ± 0.08 m
Spin0
Quadrupole Moment
0
Discovery Year1967
Parity-

234Am Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
α (α emission)0.039%
β+ SF (β+-delayed fission)0.0066%

235Am

AbundanceRadioactive ☢️
Relative Atomic Mass
235.047906478 ± 0.000056661 Da
Mass Number235
G-Factor
Half Life
10.3 ± 0.6 m
Spin5/2
Quadrupole Moment
Discovery Year1996
Parity-

235Am Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)99.6%
α (α emission)0.4%

236Am

AbundanceRadioactive ☢️
Relative Atomic Mass
236.049427 ± 0.000127 Da
Mass Number236
G-Factor
Half Life
3.6 ± 0.1 m
Spin5
Quadrupole Moment
Discovery Year1998
Parity-

236Am Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
α (α emission)4%

237Am

AbundanceRadioactive ☢️
Relative Atomic Mass
237.049995 ± 0.000064 Da
Mass Number237
G-Factor
Half Life
73.6 ± 0.8 m
Spin5/2
Quadrupole Moment
Discovery Year1970
Parity-

237Am Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)99.975%
α (α emission)0.025%

238Am

AbundanceRadioactive ☢️
Relative Atomic Mass
238.051982531 ± 0.000063243 Da
Mass Number238
G-Factor
Half Life
98 ± 3 m
Spin1
Quadrupole Moment
Discovery Year1950
Parity+

238Am Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
α (α emission)1%

239Am

AbundanceRadioactive ☢️
Relative Atomic Mass
239.053022729 ± 0.000002127 Da
Mass Number239
G-Factor
Half Life
11.9 ± 0.1 h
Spin5/2
Quadrupole Moment
Discovery Year1949
Parity-

239Am Decay Modes
Decay ModeIntensity
ϵ (electron capture)99.99%
α (α emission)0.01%

240Am

AbundanceRadioactive ☢️
Relative Atomic Mass
240.055298374 ± 0.000014849 Da
Mass Number240
G-Factor
Half Life
50.8 ± 0.3 h
Spin3
Quadrupole Moment
Discovery Year1949
Parity-

240Am Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
α (α emission)1.9%

241Am

AbundanceRadioactive ☢️
Relative Atomic Mass
241.056827343 ± 0.000001195 Da
Mass Number241
G-Factor
0.64 ± 0.004
Half Life
432.6 ± 0.6 y
Spin5/2
Quadrupole Moment
4.34 ± 0.05
Discovery Year1949
Parity-

241Am Decay Modes
Decay ModeIntensity
α (α emission)100%
SF (spontaneous fission)3.6%

242Am

AbundanceRadioactive ☢️
Relative Atomic Mass
242.059547358 ± 0.000001199 Da
Mass Number242
G-Factor
0.3854 ± 0.0017
Half Life
16.02 ± 0.02 h
Spin1
Quadrupole Moment
-2.4 ± 0.4
Discovery Year1949
Parity-

242Am Decay Modes
Decay ModeIntensity
β (β decay)82.7%
ϵ (electron capture)17.3%

243Am

AbundanceRadioactive ☢️
Relative Atomic Mass
243.061379889 ± 0.00000149 Da
Mass Number243
G-Factor
0.608 ± 0.004
Half Life
7.35 ± 0.009 ky
Spin5/2
Quadrupole Moment
4.32 ± 0.06
Discovery Year1950
Parity-

243Am Decay Modes
Decay ModeIntensity
α (α emission)100%
SF (spontaneous fission)3.7%

244Am

AbundanceRadioactive ☢️
Relative Atomic Mass
244.064282892 ± 0.0000016 Da
Mass Number244
G-Factor
Half Life
10.01 ± 0.03 h
Spin6
Quadrupole Moment
Discovery Year1950
Parity-

244Am Decay Modes
Decay ModeIntensity
β (β decay)100%

245Am

AbundanceRadioactive ☢️
Relative Atomic Mass
245.066452827 ± 0.000002024 Da
Mass Number245
G-Factor
Half Life
2.05 ± 0.01 h
Spin5/2
Quadrupole Moment
Discovery Year1955
Parity+

245Am Decay Modes
Decay ModeIntensity
β (β decay)100%

246Am

AbundanceRadioactive ☢️
Relative Atomic Mass
246.069774 ± 0.000019 Da
Mass Number246
G-Factor
Half Life
39 ± 3 m
Spin7
Quadrupole Moment
Discovery Year1955
Parity-

246Am Decay Modes
Decay ModeIntensity
β (β decay)100%

247Am

AbundanceRadioactive ☢️
Relative Atomic Mass
247.072092 ± 0.000107 Da
Mass Number247
G-Factor
Half Life
23 ± 1.3 m
Spin5/2
Quadrupole Moment
Discovery Year1967
Parity

247Am Decay Modes
Decay ModeIntensity
β (β decay)100%

248Am

AbundanceRadioactive ☢️
Relative Atomic Mass
248.075752 ± 0.000215 Da
Mass Number248
G-Factor
Half Life
Spin3
Quadrupole Moment
Discovery Year
Parity+

248Am Decay Modes
Decay ModeIntensity
β (β decay)%

249Am

AbundanceRadioactive ☢️
Relative Atomic Mass
249.07848 ± 0.00032 Da
Mass Number249
G-Factor
Half Life
Spin5/2
Quadrupole Moment
Discovery Year
Parity

249Am Decay Modes
Decay ModeIntensity
β (β decay)%

History

Americium-241 was first identified in 1944 by Glenn T. Seaborg, Ralph A. James, Leon O. Morgan and Albert Ghiorso at the metallurgical laboratory at the University of Chicago. It was produced by irradiating plutonium with neutrons during the Manhattan Project. Americium was first isolated as a pure compound by Burris Cunningham in 1945, at the University of Chicago. Named after America

DiscoverersG.T.Seaborg, R.A.James, L.O.Morgan, A.Ghiorso
Discovery LocationUnited States
Discovery Year1945
Etymology (Name Origin)Named for the American continent, by analogy with europium.
Pronunciationam-er-ISH-i-em (English)
Americium is harmful due to its radioactivity
Americium often enters landfills from discarded smoke detectors

Uses

Americium is used in commercial ionization chamber smoke detectors, as well as in neutron sources and industrial gauges. Americium-241 has been used as a portable source of both gamma rays and alpha particles for a number of medical and industrial uses. It is also used as a target material in nuclear research to make even heavier elements. Americium-241 is currently used in smoke detectors.

Sources

Produced by bombarding plutonium with neutrons.

Abundance
Abundance in Earth's crust
Abundance in Oceans
Abundance in Human Body
0 %
Abundance in Meteor
0 %
Abundance in Sun
0 %
Abundance in Universe
0 %

Nuclear Screening Constants