Lutetium-172

Main isotopes of lutetium

Iso­tope Decay abun­dance half-life mode energy (MeV) pro­duct 173Lu syn 1.37 y ε 0.671 173Yb 174Lu syn 3.31 y ε 1.374 174Yb 175Lu 97.401% is stable with 104 neutrons 176Lu 2.599% 3.78×1010 y β− 1.193 176Hf
Standard atomic weight (Ar)	174.9668(1)

Naturally occurring lutetium (₇₁Lu) is composed of 1 stable isotope ¹⁷⁵Lu (97.41% natural abundance) and one long-lived radioisotope, ¹⁷⁶Lu with a half-life of 3.78 × 10¹⁰ years (2.59% natural abundance). Thirty-four radioisotopes have been characterized, with the most stable, besides ¹⁷⁶Lu, being ¹⁷⁴Lu with a half-life of 3.31 years, and ¹⁷³Lu with a half-life of 1.37 years. All of the remaining radioactive isotopes have half-lives that are less than 9 days, and the majority of these have half-lives that are less than half an hour. This element also has 18 meta states, with the most stable being ^177mLu (t_1/2 160.4 days), ^174mLu (t_1/2 142 days) and ^178mLu (t_1/2 23.1 minutes).

The isotopes of lutetium range in atomic weight from 149.973 (¹⁵⁰Lu) to 183.961 (¹⁸⁴Lu). The primary decay mode before the most abundant stable isotope, ¹⁷⁵Lu, is electron capture (with some alpha and positron emission), and the primary mode after is beta emission. The primary decay products before ¹⁷⁵Lu are isotopes of ytterbium and the primary products after are isotopes of hafnium.

...
Wikipedia