A static gas mass spectrometer is one in which a gaseous sample for analysis is fed into the source of the instrument and then left in the source without further supply or pumping throughout the analysis. This method can be used for stable isotope analysis of light gases (as above), but it is particularly used in the isotopic analysis of noble gases (rare or inert gases) for radiometric dating or isotope geochemistry. Important examples are argon–argon dating and helium isotope analysis.