Americium (Am)

Isotopes of Americium

Isotope Atomic Mass Half-life Mode of Decay Nuclear Spin Nuclear Magnetic Moment
Am-237 237.0503 1.22 hours

EC to Pu-237;
α to Np-233

5/2 No data available
Am-238 238.05198 1.63 hours EC to Pu-238;
α to Np-234
 1 No data available 
Am-239 239.05302 11.9 hours EC to Pu-239;
α to Np-235
 5/2 No data available 
Am-240 240.05529 2.12 days EC to Pu-240;
α to Np-236
 3 No data available 
Am-241 241.05682 432.2 years α to Np-237;
 5/2 1.61
Am-242 242.05654 16.02 hours EC to Pu-242;
ß- to Cm-242
 1 0.388
Am-243 243.061375 7370 years α to Np-239;
 5/2 1.61
Am-244 244.06428 10.1 hours ß- to Cm-244  1 No data available 
Am-245 245.06644 2.05 hours ß- to Cm-245  5/2 No data available 


Americium was discovered in 1944 by Glenn T. Seaborg, Ralph A. James, Leon O. Morgan and Albert Ghiorso. It was identified as the result of successive neutron capture reactions by plutonium isotopes in a nuclear reactor in Berkeley, California, USA. It is a radioactive rare earth metal which must be handled with care to avoid contact, since it is a heavy emitter (α activity of americium-241 is about three times that of radium). Americium is available to qualified users in the UK and in the USA.

Americium is the only synthetic element to have found its way into the household, where one common type of smoke detector uses Americium-241 in the form of americium dioxide as its source of ionizing radiation. Americium appears to be more malleable than uranium or neptunium; it tarnishes slowly in dry air at room temperature. 

Properties of Americium

Name Americium
Symbol Am
Atomic number 95
Atomic weight [243]
Standard state Solid at 298 °K
CAS Registry ID 7440-35-9
Group in periodic table No Data Available
Group name Actinoids
Period in periodic table 7 (Actinoid)
Block in periodic table f-block
Color Silvery white
Classification Metallic
Melting point 1449 °K [or 1176 °C or 2149 °F]
Boiling point 2880 °K [or 2607 °C or 4725 °F]
Density of solid 13.69 g/cm3
Electron configuration [Rn]5f77s2