Cerium138

Cerium-138 (138Ce) is a stable isotope of the lanthanide element cerium, which has atomic number 58. It contains 58 protons and 80 neutrons. It is one of the naturally occurring cerium isotopes and, together with 136Ce and 140Ce, is considered to be a stable form of cerium. In natural cerium, these isotopes occur as trace components, with 140Ce present in much larger amounts; the exact fractional abundances can vary by mineral and source, but 138Ce is consistently a minor constituent.

Because 138Ce is stable, it does not undergo radioactive decay and has an effectively infinite half-life. As an even-even nucleus (both proton and neutron counts are even), its ground-state spin is expected to be 0+ in line with a common pattern among stable lanthanide isotopes, with higher-energy excited states at measurable energies.

In practice, 138Ce is mainly relevant for isotopic ratio measurements in geochemistry, cosmochemistry, and materials science. Its presence in samples contributes to the overall cerium isotopic composition used to study planetary differentiation, meteorite records, and nucleosynthetic processes in stars. Analytical methods for measuring 138Ce typically involve mass spectrometry, such as inductively coupled plasma mass spectrometry (ICP-MS) or thermal ionization mass spectrometry (TIMS), often in conjunction with other cerium isotopes to correct for mass bias and to calibrate measurements.

See also: cerium, isotopes of cerium, natural isotopes, isotopic ratio analysis.