Ring Focus in a Thin Magnetic-Lens Beta-Ray Spectrometer

Abstract

The paths of electrons in a thin magnetic‐lens type of spectrometer are described by a non‐linear differential equation. The equation was numerically integrated to obtain a set of electron trajectories originating from a point source on the axis of the instrument. Trajectories for off‐axis sources were approximated. On the basis of these trajectories, the location and some properties of ring focus were studied. Theoretically calculated line shapes are compared for axial and ring focus. For reasonable values of resolution, the transmission of the spectrometer would be roughly doubled by performing the momentum discrimination by a ring focus baffle instead of by a small counter on the axis.