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99m Tc's half-life of 6.0058 hours is considerably longer (by 14 orders of magnitude, at least) than most nuclear isomers, though not unique. This is still a short half-life relative to many other known modes of radioactive decay and it is in the middle of the range of half lives for radiopharmaceuticals used for medical imaging.
The metastable technetium-99m (99m Tc) is a short-lived (half-life about 6 hours) nuclear isomer used in nuclear medicine, produced from molybdenum-99. It decays by isomeric transition to technetium-99, a desirable characteristic, since the very long half-life and type of decay of technetium-99 imposes little further radiation burden on the body.
97m Tc is the most stable, with a half-life of 91.0 days (0.097 MeV). [4] This is followed by 95m Tc (half-life: 61 days, 0.038 MeV) and 99m Tc (half-life: 6.04 hours, 0.143 MeV). 99m Tc only emits gamma rays, subsequently decaying to 99 Tc. [7] For isotopes lighter than 98 Tc, the primary decay mode is electron capture to isotopes of molybdenum.
Molybdenum-99 has a half-life of 67 hours, so short-lived technetium-99m (half-life: 6 hours), which results from its decay, is being constantly produced. [21] The soluble pertechnetate TcO − 4 can then be chemically extracted by elution using a saline solution. A drawback of this process is that it requires targets containing uranium-235 ...
The half-life of 99 Tc is far longer than its metastable isomer, so the ratio of 99 Tc to 99m Tc increases over time. Both isomers are carried out by the elution process and react equally well with the ligand, but the 99 Tc is an impurity useless to imaging (and cannot be separated).
Radioactive isotope table "lists ALL radioactive nuclei with a half-life greater than 1000 years", incorporated in the list above. The NUBASE2020 evaluation of nuclear physics properties F.G. Kondev et al. 2021 Chinese Phys. C 45 030001. The PDF of this article lists the half-lives of all known radioactives nuclides.
It is therefore called "metastable" (hence the "m" in 99m Tc [5]). It decays to the ground state via gamma decay with a half-life of 6 hours. Decay Scheme of 210 Po. Here, to the left, we now have an alpha decay. It is the decay of the element Polonium [6] discovered by Marie Curie, with mass number 210.
In particular, 99 Tc (half-life 211,000 years) is used in corrosion research, because it is the decay product of the easily obtained commercial 99m Tc isotope. [3] Solutions of technetate(VII) react with the surface of iron to form technetium dioxide, in this way it is able to act as an anodic corrosion inhibitor .