The Electron Optical Properties of the Focal Isolation  -Ray Spectrometer

An attempt is made to show theoretically how the performance of a lens spectrometer depends upon the degree of spherical aberration present in the lens. In particular, curves of resolving power and transmission are plotted against radius and area of the central lens annulus, for source and counter window on the axis and of equal diameter. The resolving properties of a circular source and counter window placed at equal distances off the axis are determined. The arrangement is found to be impracticable. Lastly, an investigation is made into the resolving properties of a line source placed at right angles to the axis of the spectrometer, the image of which is focused into a slit-shaped window in a counter. The arrangement is shown to be advantageous particularly when long solenoids are employed, as in high energy β-spectroscopy.