A MODEL OF THE INTRINSIC EFFICIENCY OF A TIME-OF-FLIGHT SPECTROMETER FOR KEV IONS

We have constructed a first-order model of the intrinsic efficiency of a time-of-night spectrometer for medium energy ions. The spectrometer uses secondary electrons from a thin carbon foil to generate a start signal and ion impact on a microchannel plate to generate the stop sig nal. The model includes the effects of the secondary electron yield, m ultiple scattering in the foil, and the response of the individual mic rochannel plates which comprise the instrument. We describe the model and the variation of the predicted efficiency with model parameters. C omparisons with measured efficiencies for several ions and energies ra nging from 40 keV H to 500 keV O indicate that the model's predictive power is satisfactory for interpreting the results of routine surface analyses.