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Standard atomic weight Ar°(Lu) | ||||||||||||||||||||||||||||||||||||||
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Naturally occurring lutetium (71Lu) is composed of one stable isotope 175Lu (97.41% natural abundance) and one long-lived radioisotope, 176Lu with a half-life of 37 billion years (2.59% natural abundance). Forty 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 (t1/2 160.4 days), 174mLu (t1/2 142 days) and 178mLu (t1/2 23.1 minutes).
The known isotopes of lutetium range in mass number from 149 to 190. 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. All isotopes of lutetium are either radioactive or, in the case of 175Lu, observationally stable, meaning that 175Lu is predicted to be radioactive but no actual decay has been observed.[4]