Ion pulse counting

At the end of the drift tube, there is an intermediate chamber in which most of the air from the drift tube through a small orifice is pumped away. The ions in the drift tube are extracted and focused by the ion optical lens and finally, in a high vacuum chamber, are detected by a quadrupole mass spectrometer with an ion pulse counting system. The ionic count rates /(HaO" ) and 7(MH" ) are measured in counts per second, which are proportional to the respective densities of these ions. 

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