The electrons which are produced are then accelerated to the desired energy by an electric field. In this way monoenergetic electrons in a fairly narrow beam are produced and directed onto the particle detecting surface of the electrostatic analyzer. The difficulties in producing a steady monoenergetic beam of electrons are many. Perhaps the most difficult task is accurately assessing the output of the electron gun. Both the electron gun and the electrostatic analyzer itself were in need of independent calibration but in reality we used both to calibrate each other.
Problems arise in keeping the source of photons at a constant level.
If the photon source is not constant then the resulting beam is also inconstant. The electrostatic analyzer can also detect the photons from the UV source so care must be taken in keeping down the number of reflections so that light shining onto the instrument is minimized. Further problems arise from stray magnetic and electric fields which will cause a low energy beam to be deflected away from the entrance aperture. A further source of magnetic fields comes from the stepper motor used to control the position of the electrostatic analyzer. This motor had a large armature which produced a measurable magnetic field.