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Europium as a nuclear fission product

Europium is produced by nuclear fission; Eu (half-life 4.7612 years) has a fission yield of 330 parts per million (ppm) for uranium-235 and thermal neutrons. The fission product yields of europium isotopes are low near the top of the mass range for fission products.

As with other lanthanides, many isotopes of europium, especially those that have odd mass numbers or are neutron-poor like Eu, have high cross sections for neutron capture, often high enough to be neutron poisons.

Eu is the beta decay product of samarium-151, but since this has a long decay half-life and short mean time to neutron absorption, most Sm instead ends up as Sm.

Eu (half-life 13.516 years) and Eu (half-life 8.593 years) cannot be beta decay products because Sm and Sm are non-radioactive, but Eu is the only long-lived "shielded" nuclide, other than Cs, to have a fission yield of more than 2.5 parts per million fissions. A larger amount of Eu is produced by neutron activation of a significant portion of the non-radioactive Eu; however, much of this is further converted to Eu.