Atomic Properties of Tm
- Atomic Number of Tm
- 69
- Atomic Mass of Tm
- 168.9300 u
- Electron Configuration
- [Xe] 4f13 6s2
- Electronegativity
- 1.25
- Block
- f-block
- Group
- —
- Period
- 6
Per Teodor Cleve identified thulium in 1879 while separating erbium-rich material. He named it for Thule, a legendary far-northern land in classical geography. The remote name suits one of the least abundant naturally occurring lanthanides, though thulium is dispersed through rare-earth minerals rather than mined from a mythical island.
Natural thulium consists entirely of stable thulium-169. Irradiating it in a reactor can produce thulium-170, a radioactive isotope with a half-life near 128 days. Its emissions have supported compact, portable X-ray devices for specialized radiography. The device still needs shielding, careful source control, and suitable imaging geometry; “portable” does not make ionizing radiation casual.
Thulium ions also power certain lasers. Thulium-doped fiber and solid-state systems emit around two micrometers, where water absorbs strongly. That property supports selected medical procedures, materials processing, sensing, and lidar research. The laser requires a host material, pump source, optics, and cooling, with thulium acting as the light-producing dopant.
The silvery metal is relatively soft and must be separated from chemically similar rare earths. Its scarcity and cost keep most uses narrow and high-value.
This Luminary is small in market volume and focused in purpose. A reactor-made isotope can carry an X-ray source away from fixed electrical equipment, while a doped fiber can turn pump energy into controlled infrared light. Thulium works best where compactness and a particular wavelength justify an uncommon specialist.