Manganese-55

Main isotopes of manganese

iso­tope NA half-life DM DE (MeV) DP 52Mn syn 5.6 d ε – 52Cr β+ 0.575 52Cr γ 0.7, 0.9, 1.4 – 53Mn trace 3.74×106 y ε – 53Cr 54Mn syn 312 d ε 1.377 54Cr γ 0.834 – 55Mn 100% is stable with 30 neutrons
Standard atomic weight (Ar)	7001549380440000000♠54.938044(3)

Naturally occurring manganese (₂₅Mn) is composed of 1 stable isotope, ⁵⁵Mn. 25 radioisotopes have been characterized with the most stable being ⁵³Mn with a half-life of 3.7 million years, ⁵⁴Mn with a half-life of 312.3 days, and ⁵²Mn with a half-life of 5.591 days. All of the remaining radioactive isotopes have half-lives that are less than 3 hours and the majority of these have half-lives that are less than 1 minute, but only ⁴⁵Mn has an unknown half-life. The least stable is ⁴⁴Mn with a half-life shorter than 105 nanoseconds. This element also has 3 meta states.

Manganese is part of the iron group of elements, which are thought to be synthesized in large stars shortly before supernova explosion. ⁵³Mn decays to ⁵³Cr with a half-life of 3.7 million years. Because of its relatively short half-life, ⁵³Mn occurs only in tiny amounts due to the action of cosmic rays on iron in rocks. 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 ²⁶Al and ¹⁰⁷Pd for the early history of the solar system. Variations in ⁵³Cr/⁵²Cr and Mn/Cr ratios from several meteorites indicate an initial ⁵³Mn/⁵⁵Mn ratio that suggests Mn−Cr isotopic systematics must result from in-situ decay of ⁵³Mn in differentiated planetary bodies. Hence ⁵³Mn provides additional evidence for nucleosynthetic processes immediately before coalescence of the solar system.

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