The nature of the channeltron is presented in figure 3.2.
The functioning of the device in electron-counting mode is described in detail in its manual [66]. It can also be operated in a continuous current measurement mode, with a small, positive collector voltage and a sensitive ammeter connected to its front end.An electron source is also needed for the experiments; for this, a commercial electron gun is used. The experiments in section 4.4 and section 5.5 used a temporary replacement electron gun, since the gun that had been used for the experiments in section 5.4 had malfunctioned. An unfortunate consequence of a slight geometrical incompatibility, between the temporary replacement electron gun and the vacuum chamber (chapter 4,) was that low-energy electron diffraction and Auger electron spectroscopy measurements were not possible, while the temporary gun was in place; it was therefore necessary to rely on previous calibrations (sections 5.4, B,) for the kind of information that these techniques would have produced.
Both the temporary replacement electron gun, and the gun procured by the author's predecessors, are described in detail in their respective manuals [73,74].
The Mott polarimeter is an unusual, and relatively novel, instrument, and with its measurements are associated particular systematic errors; there follow descriptions of these, and of some established experimental and mathematical techniques for eliminating them.
