details on the electron beam column and the housing 1 are shown in fig4 which shows a right side view along section a a of fig3 extending to the rear are the high voltage cable 35 for the electron gun a pumping tube 36 to evacuate the electron beam column and electrical connections 37 for the lenses aperture rod 27 is preferably provided with several apertures 38 which can be selectively used to obtain different electron beam spot sizes with optimum current target holder block 29 and target holder 31 are electrically insulated from the housing and connected by means of a wire 39 to a feed through 40 this allows the target current to be monitored and also to be used as a signal for obtaining scanning images of the targets the eds detector 13 and detector collimator 13a are shown in fig4 in the position for normal operation while they are shown in a retracted position required for use of the optical viewing system in fig3 a bellows 41 allows the movement of the detector without changing the environment in the housing 1 as is commonly done with eds detectors used in scanning electron microscopes other components in fig4 are as previously identified on fig3 the crystalline materials used for.