Manganese
Isotopes

Naturally occurring manganese is composed of one stable isotope, Mn. Several radioisotopes have been isolated and described, ranging in atomic weight from 46 u (Mn) to 72 u (Mn). The most stable are Mn with a half-life of 3.7 million years, Mn with a half-life of 312.2 days, and Mn with a half-life of 5.591 days. All of the remaining radioactive isotopes have half-lives of less than three hours, and the majority of less than one minute. The primary decay mode in isotopes lighter than the most abundant stable isotope, Mn, is electron capture and the primary mode in heavier isotopes is beta decay. Manganese also has three meta states.

Manganese is part of the iron group of elements, which are thought to be synthesized in large stars shortly before the supernova explosion. Mn decays to Cr with a half-life of 3.7 million years. Because of its relatively short half-life, Mn is relatively rare, produced by cosmic rays impact on iron. Manganese isotopic contents are typically combined with chromium isotopic contents and have found application in isotope geology and radiometric dating. Mn–Cr isotopic ratios reinforce the evidence from Al and Pd for the early history of the Solar System. Variations in Cr/ Cr and Mn/Cr ratios from several meteorites suggest an initial Mn/ Mn ratio, which indicate that Mn–Cr isotopic composition must result from in situ decay of Mn in differentiated planetary bodies. Hence, Mn provides additional evidence for nucleosynthetic processes immediately before coalescence of the Solar System.
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