169Tm

169Tm, or thulium-169, is an isotope of the element thulium (atomic number 69). It has a mass number of 169, consisting of 69 protons and 100 neutrons in the nucleus. It is the only stable isotope of thulium, so natural thulium is monoisotopic with respect to 169Tm.

Because 169Tm is stable, it does not undergo radioactive decay. Consequently, there is no measurable half-life for this isotope under standard conditions, and it remains essentially constant in nature.

Occurrence and production are tied to natural thulium, which is found in rare-earth mineral deposits such as monazite and xenotime. Since 169Tm is the sole stable isotope of thulium, natural samples of thulium contain only this isotope, apart from trace impurities from other elements. Industrial isolation involves standard rare-earth mineral processing and chemical separation to obtain pure thulium metal or compounds.

In terms of chemistry and physics, 169Tm shares the characteristic properties of lanthanides. Its chemical behavior is governed by its trivalent state in most compounds, and its isotopic stability does not impart any distinct radiological activity. While 169Tm is not used for radiopharmaceuticals or other radioactive applications, it remains relevant in basic nuclear and materials research as the reference form of thulium in natural samples.

See also: Isotopes of thulium.