Thulium is a chemical element with symbol Tm and atomic number 69. It is the thirteenth and antepenultimate (third-last) element in the lanthanide series. Like the other lanthanides, the most common oxidation state is +3, seen in its oxide, halides and other compounds.
Three reasons Thulium stands out
- 1
Used in X-ray machines, superconductors, and lasers.
- 2
It is the rarest of all the naturally occurring lanthanide elements.
- 3
Its radioactive isotope is used as a compact, portable X-ray source in field medicine where power is unavailable.
The least abundant natural lanthanide
Thulium is rare even among the rare earths, which limits large-scale uses. Its ions support lasers with medical and industrial wavelengths, while irradiated thulium can become a compact X-ray source. The metal’s scarcity makes such specialized applications more sensible than bulk ones.