× 1018 years[5] which corresponds to 1 alpha decay per two minutes in every kilogram of natural europium.
The majority of the remaining radioactive isotopes, which range from 130Eu to 170Eu, have half-lives that are less than 12.2 seconds.
155Eu's large neutron capture cross section (about 3900 barns for thermal neutrons, 16000 resonance integral) 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 (nonradioactive, 350 barns thermal, 1500 resonance integral, yield is about 5 times as great as 155Eu) and 154Eu (half-life 8.6 years, 1400 barns thermal, 1600 resonance integral, fission yield is extremely small because beta decay stops at 154Sm).