Isotopes of gadolinium

Naturally occurring gadolinium (₆₄Gd) is composed of 6 stable isotopes, ¹⁵⁴Gd, ¹⁵⁵Gd, ¹⁵⁶Gd, ¹⁵⁷Gd, ¹⁵⁸Gd and ¹⁶⁰Gd, and 1 long-lived radioisotope, ¹⁵²Gd, with ¹⁵⁸Gd being the most abundant (24.84% natural abundance). The predicted double beta decay of ¹⁶⁰Gd has never been observed.

Thirty-three radioisotopes have been characterized, with the three most stable being alpha emitters: ¹⁵²Gd (naturally occurring) with a half-life of 1.08×10¹⁴ years, ¹⁵⁰Gd with a half-life of 1.79×10⁶ years, and ¹⁴⁸Gd (theoretically not beta-stable) with a half-life of 86.9 years. All of the remaining radioactive isotopes have half-lives less than a year, the majority of these having half-lives less than two minutes. There are also 10 metastable isomers, with the most stable being ^143mGd (t_1/2 = 110 seconds), ^145mGd (t_1/2 = 85 seconds) and ^141mGd (t_1/2 = 24.5 seconds).

The isotopes with atomic masses lower than the most abundant stable isotope, ¹⁵⁸Gd, primarily decay by electron capture to isotopes of europium. At higher atomic masses, the primary decay mode is beta decay to isotopes of terbium.