Experience with the use of the nuclear microprobe for determining light element distributions

Since charged-particle beams can be collimated, bent and focussed in a manner analogous to electrons, a microprobe might be designed, based upon sample irradiation with a charged-particle beam of carefully controlled proportions and measurement of the prompt radiation emitted during the bombardment process. The paper summarises experience gained with the technique during its evolution and some of the applications for which it has been found suitable. The components of the nuclear microprobe can be divided into a number of units with discrete functions: (a) the ion generating unit, (b) a mechanism for producing a small-diameter ion beam, (c) the target chamber assembly and (d) detectors and associated electronic equipment. Each of these components is considered briefly. Various techniques are summarized for the determination of the elements B, C, N, O, F and Si. As specific examples of the application of the microprobe to elemental analysis, the results for the variation of the concentration of boron across a thin sample are given. Variation of carbon concentration across a metallurgical specimen is shown and a profile for the variation of nitrogen through a stainless steel specimen is given. (T.G.)