Uranium
In nature, uranium is found as uranium-238 (99.2739–99.2752%), uranium-235 (0.7198–0.7202%), and a very small amount of uranium-234 (0.0050–0.0059%). Uranium decays slowly by emitting an alpha particle. The half-life of uranium-238 is about 4.47 billion years and that of uranium-235 is 704 million years, making them useful in dating the age of the Earth.
Europium
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.