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Americium,  95Am
Americium microscope.jpg
A small disc of americium under a microscope.

Bionerd, Americium microscope, CC BY 3.0
General properties
Name, symbol Americium, Am
Appearance Silvery-gray
Americium in the periodic table


Plutonium ← Americium → Curium
Atomic number 95
Standard atomic weight (Ar) 243
Element category Actinides
Group, block n/a; f-block
Period period 7
Electron configuration [Rn] 5f7 7s2
per shell
2, 8, 18, 32, 25, 8, 2
Physical properties
Phase Solid
Melting point 1449 K ​(1176 °C, ​2149 °F)
Density near r.t. 12 g/cm3
Heat of fusion 14.39 kJ/mol
Molar heat capacity 62.7 J/(mol·K)
Atomic properties
Oxidation states 8, 7, 6, 5, 4, 3, 2 ​(an amphoteric oxide)
Electronegativity Pauling scale: 1.3
energies 1st: 578 kJ/mol
Atomic radius empirical: 173 pm
Covalent radius 180±6 pm
Crystal structure ​Double hexagonal close-packed (dhcp)
Thermal conductivity 10 W/(m·K)
Electrical resistivity 0.69 Ω·m
Magnetic ordering Paramagnetic
CAS Registry Number 7440-35-9
Naming After the Americas
Discovery Glenn T. Seaborg, Ralph A. James, Leon O. Morgan, Albert Ghiorso (1944)
· references

Americium is a radioactive chemical element, a transuranic member of the actinide series, with symbol Am and atomic number 95. The most important isotope of this element is Americium-241 (241Am).



Like all actinides, americium reacts with air and halogens at standard conditions.


Americium is a silvery-gray metal, with a density of 12 g/cm3 at room temperature. It melts at 1176 °C and boils at 2607 °C.


Americium is readily found in smoke detectors, in the form of americium dioxide aggregate deposited on a small Al button, which is the ionization source for the smoke detector. Each radioactive button contains around 0.26 micrograms of 241Am. To obtain a significant amount of Am, you will need dozens (minimum) of Am buttons. However, acquiring lots of smoke detectors may draw the attention of the authorities.


Isolation of this element is difficult to do given the low concentration of Am in smoke detectors and its high reactivity.


  • Make your own personalized smoke detector
  • Neutron source
  • Make a spectrometer



Americium, like all actinides, is radioactive and very toxic, but the amounts encountered in smoke detector buttons are too small to pose any appreciable hazard.


Americium should be kept in thick vials, lead is also good for shielding.


Americium should be taken to centers that take care of used smoke detectors.



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