81Br

81Br is a stable isotope of the element bromine, having mass number 81 and atomic number 35. It is one of the two stable bromine isotopes, the other being 79Br. In natural bromine, 81Br accounts for about 49.3% of atoms, with 79Br contributing the remainder; together they make up almost all bromine found in nature.

The atomic mass of 81Br is approximately 80.916 unified atomic mass units. As a stable nuclide, 81Br does not undergo radioactive decay, giving it an effectively infinite natural lifetime. Its stability means that, chemically, it behaves identically to other bromine isotopes and cannot be distinguished from 79Br by typical chemical reactions.

Chemically, isotopes of an element share the same reactivity and bonding characteristics. Thus 81Br participates in the same compounds and reactions as other bromine atoms, with differences between isotopes arising only in physical properties such as mass or spectral signatures.

Natural occurrence and applications: 81Br occurs in seawater and bromine-bearing minerals as a natural constituent, contributing to the overall isotopic composition of bromine on Earth. The isotopic abundances of bromine isotopes, including 81Br, are used in geochemical and environmental studies, as well as in mass spectrometry and isotope ratio analyses to investigate sources, processes, and cycles involving bromine.