Molybdenum (₄₂Mo) has seven isotopes in nature, with atomic masses of 92, 94-98, and 100. All are stable except¹⁰⁰Mo, which undergoesdouble beta decay with ahalf-life of 7.07×10¹⁸ years (theshortest known for this mode) to¹⁰⁰Ru.⁹²Mo and⁹⁸Mo are also energetically able to decay in this manner, to zirconium and ruthenium respectively; the others are theoretically stable. There are also a total of 32 syntheticisotopes known, and at least 13 metastablenuclear isomers, ranging inatomic mass from 81 to 119.

The isotopes with mass 93 or lower decay byelectron capture or positron emission toniobium isotopes (orzirconium after delayed proton emission); those with mass 99 or higher by ordinarybeta decay totechnetium. The most stable of the former are⁹³Mo, recently measured to have a half-life around 4800 years,^[2] and⁹⁰Mo at 5.56 hours. The most stable of the latter is the medically important⁹⁹Mo, half-life 65.932 hours, and whose decay leads to thechief isotope of technetium. By far the most stable isomer is^93m1Mo at 6.85 hours, decaying to its ground state.

Molybdenum-99 is produced commercially by intense neutron-bombardment (i.e.fission) of a highly purifieduranium-235 target, followed rapidly by extraction.^[9] It is used as a parent radioisotope intechnetium-99m generators to produce the even shorter-lived daughter isotopetechnetium-99m, which is used in approximately 40 million medical procedures annually. A common misunderstanding or misnomer is that⁹⁹Mo is used in these diagnostic medical scans, when actually it has no role in the imaging agent or the scan itself. In fact,⁹⁹Mo co-eluted with the^99mTc (also known as breakthrough) is considered a contaminant and is minimised to adhere to the appropriateUSP (or equivalent) regulations and standards. The IAEA recommends that⁹⁹Mo concentrations exceeding more than 0.15 μCi/mCi^99mTc or 0.015% should not be administered for usage in humans.^[10] Typically, quantification of⁹⁹Mo breakthrough is performed for every elution when using a⁹⁹Mo/^99mTc generator during QA-QC testing of the final product.

There are alternative routes for generating⁹⁹Mo that do not require a fissionable target, such as high or low enriched uranium (i.e., HEU or LEU). Some of these include accelerator-based methods, such as proton bombardment orphotoneutron reactions on enriched¹⁰⁰Mo targets. Historically,⁹⁹Mo generated by neutron capture on natural isotopic molybdenum or enriched⁹⁸Mo targets was used for the development of commercial⁹⁹Mo/^99mTc generators.^[11][12] The neutron-capture process was eventually superseded by fission-based⁹⁹Mo that could be generated with much higher specific activities. Implementing feed-stocks of high specific activity⁹⁹Mo solutions thus allowed for higher quality production and better separations of^99mTc from⁹⁹Mo on small alumina column usingchromatography. Employing low-specific activity⁹⁹Mo under similar conditions is particularly problematic in that either higher Mo loading capacities or larger columns are required for accommodating equivalent amounts of⁹⁹Mo. Chemically speaking, this phenomenon occurs due to other Mo isotopes present aside from⁹⁹Mo that compete for surface site interactions on the column substrate. In turn, low-specific activity⁹⁹Mo usually requires much larger column sizes and longer separation times, and usually yields^99mTc accompanied by unsatisfactory amounts of the parent radioisotope when usingγ-alumina as the column substrate. Ultimately, the inferior end-product^99mTc generated under these conditions makes it essentially incompatible with the current supply chain.

In the last decade, cooperative agreements between the US government and private capital entities have resurrected neutron capture production for commercially distributed⁹⁹Mo/^99mTc in the United States of America.^[13] The return to neutron-capture-based⁹⁹Mo has also been accompanied by the implementation of novel separation methods that allow for low-specific activity⁹⁹Mo to be utilized.^{[citation needed]}

Daughter products other than molybdenum

• Isotopes of technetium
• Isotopes of niobium
• Isotopes of zirconium

• Isotopes of molybdenum
• Molybdenum
• Lists of isotopes by element

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