The optical properties of axially symmetric magnetic prismspart 1: The study of rays in a plane of symmetry, and its application to the design of prism -spectroscopes

The optical properties of the magnetic field in the neighbourhood of two equal co-axial magnetic poles of opposite polarity used as a magnetic prism are discussed. In this first part attention is confined to rays in the plane of symmetry between the poles over which the radial component of the field vanishes everywhere. The focusing properties and aberrations are discussed generally, and detailed calculations are given: by simple analytical methods for the case of zero pole separation (homogeneous field); by numerical computation for the case of a pole separation equal to the radius of either pole. Inferences are drawn concerning the use of such fields in β-spectroscopy, and it is shown that under certain conditions image formation by the prisms is optically corrected over a very wide aperture, or under other conditions can be corrected in compound instruments conssiting of the prism and one or more magnetic lenses. Thus very high resolution is possible in such instruments. The overall optimum design for a β-spectroscope, however, cannot be made without a consideration of the focusing towards the plane of symmetry of rays confined to that plane. This focusing will be considered in Part 2.