Multiple ion detection system with miniscan facilities and expanded mass range for magnetic sector mass spectrometers.

Abstract

A new four-channel multiple ion detection (MID) system is described. By adding a A V of up to 1100 volts to the nominal accelerating voltage ( V ) , a mass range of about 3 0 % ( V = 3600 volts) to 9 0% ( V = 1200 volts) can be covered, thus providing a remarkably wide range compared to other MID units. The system incorporates a ramp voltage, which added to V allows a small scan around each one of the peaks fo- cused, as well as holding amplifiers in each channel. These features combined with the excellent stability of the Ionization chamber against voltage changes mlnlmlre the errors due to defocusing effects, permitting the addition of voltages as high as those described. The scan time is continuously adjustable between 0.5 and 12 s and the swltching time between two adjacent channels is 50 ms. The circuit design, its operation, and some aspects of the performance of this unit are described.