Open AccessInstrumentation for negative ion detection.
Author(s) -
Michael R. McKeown
Publication year - 1980
Publication title -
environmental health perspectives
Language(s) - Danish
Resource type - Journals
SCImago Journal Rank - 2.257
H-Index - 282
eISSN - 1552-9924
pISSN - 0091-6765
DOI - 10.1289/ehp.803697
Subject(s) - preamplifier , electron multiplier , ion , biasing , spectrometer , physics , multiplier (economics) , mass spectrometry , atomic physics , decoupling (probability) , instrumentation (computer programming) , waveform , voltage , computational physics , optoelectronics , optics , computer science , engineering , amplifier , cmos , quantum mechanics , control engineering , economics , macroeconomics , operating system
The instrumentation and practical circuitry required for the detection of negative ions exiting the mass analysis section of a mass spectrometer is examined. The potentials needed to bias the electron multiplier when detecting negative ions from a low ion-energy mass spectrometer, e.g., a quadrupole, are contrasted with the biasing requirements of a mass spectrometer having high ion-energies, e.g., a magnetic sector. Methods of decoupling the biasing high voltage on the signal lead of the multiplier in pulse counting measurements are discussed in detail so that normal, ground referenced input, pulse preamplifiers may be used. Easily understood, practical rules for determining the values of circuit components are given together with a simplified theory of transferring pulse signals from multiplier collector to pulse preamplifier. The changes in circuitry needed when attempting to detect ions by current measurement methods from an electron multiplier area detailed. The effects of leakage currents into athe input of the current preamplifier and their avoidance bay using triaxial shielding on vacuum feed-throughs are explained. The article suggests possible methods of decoupling the high voltage referenced input and the ground referenced output of a current measuring preamplifier.