has 33 known isotopes, ranging in atomic mass from 83 to 115, as well as four metastable nuclear isomers. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. All unstable isotopes of molybdenum decay into isotopes of zirconium, niobium, technetium, and ruthenium. Molybdenum-100 is the only naturally occurringisotope that is not stable. Molybdenum-100 has a half-life of approximately 1×1019y and undergoes double beta decay into ruthenium-100. Molybdenum-98 is the most common isotope, comprising 24.14% of all molybdenum on Earth. Molybdenum isotopes with mass numbers 111 and up all have half-lives of approximately.15 s.
Molybdenum-99 is produced commercially by intense neutron-bombardment of a highly purified uranium-235 target, followed rapidly by extraction. It is used as a parent radioisotope in technetium-99m generators to produce the even shorter-lived daughter isotope technetium-99m, which is used in approximately 40 million medical procedures annually. A common misunderstanding or misnomer is that 99Mo 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 is considered a contaminant and is minimised to adhere to the appropriate USP regulations and standards. The IAEA recommends that 99Mo concentrations exceeding more than 0.15µCi/mCi 99mTc or 0.015% should not be administered for usage in humans. Typically quantification of 99Mo breakthrough is performed for every elution when using a 99Mo/99mTc generator during QA-QC testing of the final product. There are alternative routes for generating 99Mo that do not require a fissionable target, such as high or low enriched uranium. Some of these include accelerator-based methods, such as proton bombardment or photoneutron reactions on enriched 100Mo targets. Historically, 99Mo generated by neutron capture on natural isotopic molybdenum or enriched 98Mo targets was used for the development of commercial 99Mo/99mTc generators, but this process was made obsolete by fission-based 99Mo, which could be generated with much higher specific activity. More recently, cooperative agreements between the US government and private capital entities have resurrected neutron capture production for commercially distributed 99Mo/99mTc in the United States of America. Primary advantages of these non-fission-based techniques are: much less radioactive waste associated with processing, reduction of nuclear proliferation, and some do not necessitate the use of a nuclear reactor. More exotic 99Mo production routes include ordinary muon capture reactions on natural molybdenum or enriched 100Mo.
