Helium is a gas naturally generated by the radio nuclides present in gold (uranium and thorium), which evaporates during the melting of the metal. Once cooled, a new helium forms and remains as prisoner of gold. Measuring its concentration and the content of radioactive elements allows to find the antiquity of the last melting of the metal.
Requiring few material (several hundred of milligrams), the measurement supposes a high technicality and a dedicated equipment (transformed mass spectrometer). This explains why so few laboratories around the world offer this analysis, which is of great interest for the scientific expertise of gold objects.
However, low concentrations of residual helium to be detected involve high uncertainty of measurement that sometimes makes the results difficult to interpret.
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