Europium-155

Europium-155 is a radioisotope or Europium and fission product with a halflife of 4.76 years. It has a maximum decay energy of 252 KeV. In a thermal reactor (almost all current nuclear power plants), it has a low fission product yield, about half of one percent as much as the most abundant fission products.

Eu-155'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 halflife are all far less than Cs-137 and Sr-90, so Eu-155 is not a significant contributor to nuclear waste.

Some Eu-155 is also produced by successive neutron capture on Eu-153 (nonradioactive, 350 barns thermal, 1500 resonance integral, yield is about 5 times as great as Eu-155) andEu-154 (halflife 8.6 years, 1400 barns thermal, 1600 resonance integral, fission yield is extremely small because beta decay stops at Sm-154); however the differing cross sections mean that both Eu-155 and Eu-154 are destroyed faster than they are produced.Eu-154 is a prolific emitter of gamma radiation. [http://www-nds.ipen.br/sgnucdat/b2.pdf]

ee also

*Isotopes of europium