Technetium-97

Main isotopes of technetium

Iso­tope Decay abun­dance half-life mode energy (MeV) pro­duct 95mTc syn 61 d ε – 95Mo γ 0.204, 0.582, 0.835 – IT 0.0389, e 95Tc 96Tc syn 4.3 d ε – 96Mo γ 0.778, 0.849, 0.812 – 97Tc syn 2.6×106 y ε – 97Mo 97mTc syn 91 d IT 0.965, e 97Tc 98Tc syn 4.2×106 y β− 0.4 98Ru γ 0.745, 0.652 – 99Tc trace 2.111×105 y β− 0.294 99Ru 99mTc syn 6.01 h IT 0.142, 0.002 99Tc γ 0.140 –

Technetium (₄₃Tc) is the first of the two elements lighter than bismuth that have no non-radioactive isotopes; the other such element is promethium. It is primarily artificial, only trace quantities existing in nature produced by spontaneous fission or neutron capture by molybdenum. The first isotopes to be synthesized were ⁹⁷Tc and ⁹⁹Tc in 1936, the first artificial element to be produced. The most stable radioisotopes are ⁹⁸Tc (half-life of 4.2 million years), ⁹⁷Tc (half-life: 2.6 million years) and ⁹⁹Tc (half-life: 211,100 years).

Thirty-three other radioisotopes have been characterized with atomic masses ranging from ⁸⁵Tc to ¹²⁰Tc. Most of these have half-lives that are less than an hour; the exceptions are ⁹³Tc (half-life: 2.75 hours), ⁹⁴Tc (half-life: 4.883 hours), ⁹⁵Tc (half-life: 20 hours), and ⁹⁶Tc (half-life: 4.28 days).

Technetium also has numerous meta states. ^97mTc is the most stable, with a half-life of 90.1 days (0.097 MeV). This is followed by ^95mTc (half-life: 61 days, 0.038 MeV), and ^99mTc (half-life: 6.04 hours, 0.143 MeV). ^99mTc only emits gamma rays, subsequently decaying to ⁹⁹Tc.

For isotopes lighter than the most stable isotope, ⁹⁸Tc, the primary decay mode is electron capture, giving molybdenum. For the heavier isotopes, the primary mode is beta emission, giving ruthenium, with the exception that ¹⁰⁰Tc can decay both by beta emission and electron capture.

Technetium-99 is the most common and most readily available isotope, as it is a major fission product from fission of actinides like uranium and plutonium with a fission product yield of 6% or more, and in fact the most significant long-lived fission product. Lighter isotopes of technetium are almost never produced in fission because the initial fission products normally have a higher neutron/proton ratio than is stable for their mass range, and therefore undergo beta decay until reaching the ultimate product. Beta decay of fission products of mass 95-98 stops at the stable isotopes of molybdenum of those masses and does not reach technetium. For mass 100 and greater, the technetium isotopes of those masses are very short-lived and quickly beta decay to isotopes of ruthenium. Therefore, the technetium in spent nuclear fuel is practically all ⁹⁹Tc.

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