166Er

166Er is a stable isotope of the element erbium (Er) with mass number 166. It has 68 protons, the atomic number of erbium, and 98 neutrons, giving it a neutron-to-proton ratio characteristic of mid-heavy lanthanides. As an even-even nucleus (both Z and N are even), 166Er is expected to have a 0+ ground state and does not undergo radioactive decay.

Natural occurrence and abundance: 166Er is one of the six stable isotopes of erbium. In natural samples of erbium, 166Er accounts for roughly one third of the total erbium present, alongside other stable isotopes such as 162Er, 164Er, 167Er, 168Er, and 170Er. Because it is stable, 166Er is not associated with a radioactive half-life.

Nuclear properties and context: The stability of 166Er makes it a component of the natural isotopic composition of erbium and a subject of study in nuclear structure and abundance analyses. Its presence helps researchers understand neutron-rich configurations in stable lanthanide nuclei and contributes to calibrations in isotopic-ratio measurements.

Applications: While 166Er itself is not a radionuclide, stable erbium isotopes, including 166Er, are used in isotopic abundance studies, materials analysis, and reference measurements in spectroscopy and geochemistry. They provide a baseline for comparing synthetic or altered samples.

See also: erbium; isotopes of erbium.