The assessment of relative electron gun performance Comments on the paper entitled 'Digital computer studies of electron guns for electron microscopes'

A method of comparing the basic performance of electron guns is described. The method is applied to some recently computed results on two versions of an electron gun which has a hairpin-filament cathode.
In an interesting and useful paper by Worster (1979 a), hereafter referred to as JW, computed results are given relating to two electron guns. When the performance of the guns was compared it was concluded that one gun was better than the other in all respects. However, in making the comparison the electron beam divergence was not taken into account. Although the method of comparison used in JW may, of course, be satisfactory for some purposes, the computed results in JW are comprehensive enough to provide information for an alternative method of comparison which includes beam divergence. Such an alternative method, described in this note, leads to different conclusions. [ABSTRACT FROM AUTHOR]