Ar-Ar dating laboratory
4) Argon counting system

Back to spectrometer...

In addition to saved values in a computer, a printer shows measurements of mass spectrometer. Some argon peaks are well visible, such as argon 40, 39 and 38. Masses 37 and 36 are in too low quantity to be revealed on this scale. In the argon laboratory of Berne, only one collector is present in spectrometer; each mass is so measured by turns. 12 to 13 measurement cycles are necessary for each (this makes a total of 60 to 65 measurements). Intensity of each masses evolves with time, as the analysed gas is slowly mixed and equilibrated with the few quantities of gas already present in mass spectrometer (background of spectrometer). We thus have to apply a linear or exponential regression over the time to get the correct value of the gas to analyse (the gas composition at its entry in spectrometer). In the green frame, three measurement cycles are present and we can see a clear decrease of 39Ar intensity and a slight increase of 40Ar.

END (for the moment... ;-)

Fig. 1, Printer showing the argon masses signals (well seen here are ³⁶Ar, ³⁹Ar and ⁴⁰Ar, the other peaks beeing to small to be shown here...).