Fast-Pulse Detection for Isotopic Abundance Determination By Resonance Ionization, Time-Of-Flight Mass Spectrometry

Publisher Website
Google Scholar
Abstract
A linear time-of-flight mass spectrometer with static electrode voltages was developed for isotopic abundance measurements and showed good resolving power (620) for atomic ions. Positive ions, produced by multiphoton excitations, were detected by a microchannel plate detector that featured low noise and good pulse height distribution. Signal pulses were too fast for precise quantification by currently available transient digitizers. A gated pulse counter, which used AND logic circuitry to direct pulses for different isotopes into separate channels of a counter, was developed for quantification of the signal pulses and results for isotopic ratio measurements showed good precision, 0.3% to 1% relative standard deviation. The time-of-flight mass spectrometer with gated pulse counter was particularly well matched to pulsed laser ionization, because it could detect all isotopes of the selected element ionized in each laser pulse, and it did not impose a limit on the laser pulse repetition rate.