An optical column for a scanning positron microprobe is described. A beam 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*0.6 mm2 is formed using electron optical elements that are already well known but rarely used in an optical column. The idea allows the construction of a sample chamber free of material and electric fields in a hemisphere above the sample with a radius of some 100 mm or more. The absence of diaphragms and 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 available, which makes a system with a very high transmission essential. Although the idea was created for a positron microprobe, other applications, such as with a retarding field analyser introduced into the sample chamber, are conceivable.    «

An optical column for a scanning positron microprobe is described. A beam 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*0.6 mm2 is formed using electron optical elements that are already well known but rarely used in an optical column. The idea allows the construction of a sample chamber free of material and electric fields in a hemisphere above the sample with a radius of some 100 mm or more. The absence of diaphragms and the comforta...    »