Thulium-166

Main isotopes of thulium

Iso­tope Decay abun­dance half-life mode energy (MeV) pro­duct 167Tm syn 9.25 d ε 0.748 167Er 168Tm syn 93.1 d ε 1.679 168Er 169Tm 100% is stable with 100 neutrons 170Tm syn 128.6 d β− 0.968 170Yb 171Tm syn 1.92 y β− 0.096 171Yb
Standard atomic weight (Ar)	7002168934220000000♠168.93422(2)

Naturally occurring thulium (₆₉Tm) is composed of 1 stable isotope, ¹⁶⁹Tm (100% natural abundance). Thirty-four radioisotopes have been characterized, with the most stable being ¹⁷¹Tm with a half-life of 1.92 years, ¹⁷⁰Tm with a half-life of 128.6 days, ¹⁶⁸Tm with a half-life of 93.1 days, and ¹⁶⁷Tm with a half-life of 9.25 days. All of the remaining radioactive isotopes have half-lives that are less than 64 hours, and the majority of these have half-lives that are less than 2 minutes. This element also has 26 meta states, with the most stable being ^164mTm (t_1/2 5.1 minutes), ^160mTm (t_1/2 74.5 seconds) and ^155mTm (t_1/2 45 seconds).

The isotopes of thulium range in atomic weight from 144.97007 u (¹⁴⁵Tm) to 178.95534 u (¹⁷⁹Tm). The primary decay mode before the most abundant stable isotope, ¹⁶⁹Tm, is electron capture, and the primary mode after is beta emission. The primary decay products before ¹⁶⁹Tm are erbium isotopes, and the primary products after are ytterbium isotopes.

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