Pulse counting technique and mass filter

Technical and practical problems are discussed in combining the ion-pulse counting method with a quadrupole mass filter. To eliminate the interference of high frequency voltage applied to the quadrupole rods, an appropriate combination of time constant values was chosen for the CR-RC circuit in the linear amplifier of an usual counting system. Tests with a selected combination have shown that extremely low ion currents less than 1-0.1 counts per sec(cps) are possible to be measured with a background counts around 0.02-0.05 cps. With this measuring condition, residual gas analysis of 10-7 Torr can be made by using only 10-11 amp. of electron bombarding currents. Some other interesting results which were obtained with the low bombarding currents are also described.