Isotopes of europium


Naturally occurring europium is composed of 2 isotopes, 151Eu and 153Eu, with 153Eu being the most abundant. While 153Eu is observationally stable, 151Eu was found in 2007 to be unstable and undergo alpha decay. The half-life is measured to be ± 0.68) × 1018 y which corresponds to 1 alpha decay per two minutes in every kilogram of natural europium. Besides the natural radioisotope 151Eu, 36 artificial radioisotopes have been characterized, with the most stable being 150Eu with a half-life of 36.9 years, 152Eu with a half-life of 13.516 years, 154Eu with a half-life of 8.593 years, and 155Eu with a half-life of 4.7612 years. The majority of the remaining radioactive isotopes have half-lives that are less than 12.2 seconds. This element also has 17 meta states, with the most stable being 150mEu, 152m1Eu and 152m2Eu.
The primary decay mode before the most abundant stable isotope, 153Eu, is electron capture, and the primary mode after is beta decay. The primary decay products before 153Eu are isotopes of samarium and the primary products after are isotopes of gadolinium.

List of isotopes

Europium-155

Europium-155 is a fission product with a half-life of 4.76 years. It has a maximum decay energy of 252 keV. In a thermal reactor, it has a low fission product yield, about half of one percent as much as the most abundant fission products.
155Eu's large neutron capture cross section means that most of even the small amount produced is destroyed in the course of the nuclear fuel's burnup. Yield, decay energy, and half-life are all far less than that of 137Cs and 90Sr, so 155Eu is not a significant contributor to nuclear waste.
Some 155Eu is also produced by successive neutron capture on 153Eu and 154Eu. However, the differing cross sections mean that both 155Eu and 154Eu are destroyed faster than they are produced.
154Eu is a prolific emitter of gamma radiation.
IsotopeHalflifeRelative yieldThermal neutronResonance integral
Eu-153Stable53501500
Eu-1548.6 yearsNearly 015001600
Eu-1554.76 years1390016000