AMERICUM Am      Z = 95

This transuranium element was discovered by T. Seaborg, R. James, L. Morgan and A. Ghiorso in Chicago in 1944. Its name alludes to America.

Ionization energies

AmI 6.0 eV

Several lines of AmII were found by Jaschek and Brandi (1972) in the spectrum of one Ap star of the Cr-Eu-Sr subgroup. The authors regarded this identification as dubious because of the lack of agreement with laboratory line intensities.

Later work did not confirm the presence of this transuranium element.


The longest lived isotope of this unstable element (Am243) has a half life of 7.4 × 103 years. A total of 13 isotopes and isomers exist.


Am is produced by the r process.

Published in "The Behavior of Chemical Elements in Stars", Carlos Jaschek and Mercedes Jaschek, 1995, Cambridge University Press.