A NEW OPTICAL-COLUMN FOR A SCANNING POSITRON MICROSCOPE

An optical column for a scanning positron microprobe is described. A b eam of variable energy from 1 to 30 keV and a spot diameter of 1 mu m, that can be scanned over an area of 0.6 x 0.6 mm(2) is formed using e lectron optical elements that are already well known but rarely used i n an optical column. The idea allows the construction of a sample cham ber free of material and electric fields in a hemisphere above the sam ple with a radius of some 100 mm or more. The absence of diaphragms an d the comfortable inner diameter of the lenses used makes it possible to work with a beam of comparatively large diameter and aperture. This is necessary because of the low intensity of the positron sources ava ilable, which makes a system with a very high transmission essential. Although the idea was created for a positron microprobe, other applica tions, such as with a retarding field analyser introduced into the sam ple chamber, are conceivable.