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Occurrence and production

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 Tc and Tc are only 4.2 million years. More than a thousand of such periods have passed since the formation of the Earth, so the probability of survival of even one atom of primordial technetium is effectively zero. However, small amounts exist as spontaneous fission products in uranium ores. A kilogram of uranium contains an estimated 1 nanogram (10 g) equivalent to ten trillion atoms of technetium. Some red giant stars with the spectral types S-, M-, and N display a spectral absorption line indicating the presence of technetium. These red giants are known informally as technetium stars.