In 1937 Emilio Segrč and Carlo Perrier created Technetium by bombarding Molybdenum targets with deuterons (particles consisting of a proton and a neutron), the first element to be created artificially. Because Technetium is not part of the decay series of any naturally radioactive element , scientists had thought that Technetium does not occur in nature. In 1988, however, minute quantities of it were detected in ore from a deep Molybdenum mine in Colorado. An extremely small amount of Technetium can be created naturally in sustained underground nuclear reactions estimated to have occurred in Gabon, Africa and a few other locations. This phenomenon occurs because much higher concentrations of Uranium-235 were present at that time; the current Uranium-235 concentration, about 0.72%, will not sustain such natural reactions. Technetium isotopes ranging in mass number from 90 to 111 are now known; the most common isotopes has a mass numbers of 97 and 98. Technetium is chemically active and useful in that it forms oxides, sulfides, and technetiates, such as ammonium technetiate (NH 4TcO4). Compounds and alloys containing technetium oxide can prevent the corrosion of iron by water. Technetium-99 is used for imaging in medicine.
Spectral analysis of star light indicates that Technetium is found in stars. Technetium is often, but not always detected in M, MS, MC, S and C type stars. Since Technetium has no stable isotopes and the longest lived isotope has a half life of 4.2 million years, detection in the atmosphere of a star means it has been synthesized recently by neutron capture and subsequently dredged up from lower layers onto the surface by a not well understood process where it can be spectrally detected.
In 1946 George Gamow had suggested that nucleosynthesis was associated with events at the origin of the Universe, while Fred Hoyle and others had suggested that ALL the elements heavier than Helium had been made in the furnaces of stars, but nobody could see a way in which these heavy elements could be formed, nor was there any experimental evidence of nucleosynthesis in stars. The 'smoking gun' was discovered in 1952 when Paul Merrill identified the spectrum of the element of Technetium in certain S type (red giant) stars. The element Technetium is special in that it is unknown in the crust of the Earth, because it has NO stable isotopes! Even its most stable isotopes, Technetium-97 and 98 have half lives of only about 2.6 and 4.2 million years, so that in an old age solar system model this element would have vanished from the Earth. The observation of Technetium in stars showed that nucleosynthesis was not confined to the early period of the Universe, but was happening now! Later observation of supernovae explosions showed evidence that the output of light from the star followed the characteristic curve associated with radioactive decay - in particular the 6 day half life of Nickel-56 and the 77 day half life of Cobalt-56. Here was direct evidence of the production of elements including Technetium in exploding stars.