…composed of the stable isotope thulium-169. Thirty-five radioactive isotopes (excluding nuclear isomers) are known. They range in mass from 144 to 179, and their half-lives range from more than 300 nanoseconds (thulium-178) to 1.92 years (thulium-171). Bombarded by neutrons, natural thulium becomes radioactive thulium-170 (128.6-day half-life), which ejects soft
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