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For technetium-98 and heavier isotopes, the primary mode is beta emission (the emission of an electron or positron), producing ruthenium (Z = 44), with the exception that technetium-100 can decay both by beta emission and electron capture. [59] [60] Technetium also has numerous nuclear isomers, which are isotopes with one or more excited nucleons.
Both of these decay modes rearrange the nucleons without transmuting the technetium into another element. 99m Tc decays mainly by gamma emission, slightly less than 88% of the time. ( 99m Tc → 99 Tc + γ) About 98.6% of these gamma decays result in 140.5 keV gamma rays and the remaining 1.4% are to gammas of a slightly higher energy at 142.6 keV.
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.
The mechanism for the creation of a synthetic element is to force additional protons into the nucleus of an element with an atomic number lower than 95. All known (see: Island of stability) synthetic elements are unstable, but they decay at widely varying rates; the half-lives of their longest-lived isotopes range from microseconds to millions ...
Technetium was created by bombarding molybdenum atoms with deuterons that had been accelerated by a device called a cyclotron. Technetium occurs naturally in the Earth's crust in minute concentrations of about 0.003 parts per trillion. Technetium is so rare because the half-lives of 97 Tc and 98 Tc are only 4.2 million
Each chemical element has a unique atomic number (Z— for "Zahl", German for "number") representing the number of protons in its nucleus. [4] Each distinct atomic number therefore corresponds to a class of atom: these classes are called the chemical elements. [5] The chemical elements are what the periodic table classifies and organizes.
The other two types of decay are observed in all the elements. Lead, atomic number 82, is the heaviest element to have any isotopes stable (to the limit of measurement) to radioactive decay. Radioactive decay is seen in all isotopes of all elements of atomic number 83 or greater.
[2] [3] Technetium and promethium (atomic numbers 43 and 61, respectively [a]) and all the elements with an atomic number over 82 only have isotopes that are known to decompose through radioactive decay. No undiscovered elements are expected to be stable; therefore, lead is considered the heaviest stable element.