A compact cylindrical Mott electron polarimeter operating with accelerating voltage in the range 20-100 kV

Abstract

The design and performance of a compact Mott detector of electron polarisation based on a concentric cylinder electrode geometry is described. Electrons accelerated in the cylindrical field are scattered from a gold foil and decelerated in the same field before detection. The resultant rejection of inelastically scattered electrons is shown to permit efficient operation of the polarimeter with an accelerating potential as low as 20 kV and an effective Sherman function greater than 0.2. The dependence of the measured asymmetry on foil thickness and on energy-loss threshold has been studied; extrapolation to zero energy loss is shown to provide a convenient method of estimating multiple and plural scattering effects. The dependence on scattering energy of the Sherman function for single scattering has thus been evaluated between 20 and 100 keV and found to be in agreement with the calculation of Holzwarth and Meister, in contrast to earlier experimental work.