FUNDAMENTALS OF FOCAL-PLANE DETECTORS

spatial dispersion of ions in one dimension is a well established mean s of analysing ion mass nod focal plane detectors (FPDs) allow ions of a wide range of masses to be recorded simultaneously. This paper is c oncerned with the principles governing the performance of FPDs and the types of FPD available. It is focused on magnetic sector mass spectro metry but is relevant to all applications in which spatially dispersed particles can be detected using a microchannel plate electron multipl ier, e.g. ions, photons of wavelength <200 nm, electrons and energetic neutrals. Although it has proved possible to produce mass spectra wit h a high resolution, this has not been matched by an ability to detect them efficiently. Given that highly resolved spectra are available at the detector but are inaccessible efficiently, it is in the developme nt of high-performance FPDs where there are enormous gains in efficien cy to be achieved. Limitations of FPD performance of two fundamental t ypes are discussed: the position of impact of an ion on the FPD cannot be measured exactly, and the upper and lower count rates of the FPD a re both restricted. These limitations Pre not simply characterized but are sometimes determined by the electron multiplier stage, sometimes by the properties of the array and sometimes by the data acquisition s ystem. (C) 1997 by John Wiley & Sons, Ltd.