Europium-151

Main isotopes of europium

Iso­tope Decay abun­dance half-life mode energy (MeV) pro­duct 150Eu syn 36.9 y ε 2.261 150Sm 151Eu 47.8% 5×1018 y α 1.9644 147Pm 152Eu syn 13.54 y ε 1.874 152Sm β− 1.819 152Gd 153Eu 52.2% is stable with 90 neutrons 154Eu syn 8.59 y β− 1.969 154Gd 155Eu syn 4.76 y β− 0.253 155Gd
Standard atomic weight (Ar)	151.964(1)

Naturally occurring europium (₆₃Eu) is composed of 2 isotopes, ¹⁵¹Eu and ¹⁵³Eu, with ¹⁵³Eu being the most abundant (52.2% natural abundance). While ¹⁵³Eu is observationally stable, ¹⁵¹Eu was recently found to be unstable and to undergo alpha decay. The half-life is measured to be (4.62 ± 0.95(stat.) ± 0.68(syst.)) × 10¹⁸ y which corresponds to 1 alpha decay per two minutes in every kilogram of natural europium. Besides natural radioisotopes ¹⁵¹Eu and ¹⁵³Eu, 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 (t_1/2 12.8 hours), ^152m1Eu (t_1/2 9.3116 hours) and ^152m2Eu (t_1/2 96 minutes).

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.

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 (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.

...
Wikipedia