barium138

Barium-138 (138Ba) is a stable isotope of the element barium, which has atomic number 56 and mass number 138. It consists of 56 protons and 82 neutrons. In natural barium, 138Ba is the most abundant stable isotope, forming the majority of the element’s terrestrial abundance.

Stability and structure: 138Ba is non-radioactive and, as an even-even nucleus, its ground state has spin and parity of 0+. Its stability means it does not undergo radioactive decay under ordinary conditions.

Nucleosynthesis and occurrence: 138Ba is produced in stars primarily by the slow neutron capture process (the s-process). Through successive neutron captures on neighboring isotopes, stable isotopes such as 137Ba can capture neutrons to form 138Ba, which remains stable and becomes part of the stellar and galactic Ba inventories released into the interstellar medium.

Properties and measurements: As a major stable constituent of natural barium, 138Ba is often used in isotope ratio studies to calibrate mass spectrometric measurements and to interpret cosmochemical and geochemical samples. Its presence helps constrain models of nucleosynthesis and the chemical evolution of the Solar System.

Applications and safety: While barium compounds are toxic if ingested or inhaled, the 138Ba isotope itself is not radiotoxic given its stability. In practice, isotopic 138Ba measurements are routine in analytical chemistry, geochemistry, and cosmochemistry.

See also: Isotopes of barium.