Further Studies - Experimental and Theoretical - of a Wide-Angle -Spectrometer which uses a Prolate Spheroidal Magnetic Field

Abstract

A β-spectrometer is described which focuses a conical sheaf of rays emitted at about 80° to the axis of a prolate spheroidal magnetic field. In agreement with a previous theoretical prediction, the trajectories cross over at two sites in the rotating meridional plane. The field behaves in some ways like a magnetic mirror and can be arranged to form an aberration-free image of a point on the axis of symmetry. It cannot, however, give a clear image of an area because the Abbe sine condition is not fulfilled. The wide-angle focusing action is compared with that recently found by Slatis and Siegbahn, for which a different optical analogue is suggested, based on the isolation of a meridional focal line between two refractions The adjustment of the spectrometer and measurements of its resolving power and solid angle of collection are described, an example being 1.4% of 4π with a line-width of 1/113 at half-height. By working at less than unit magnification it is possible to focus rays emitted at less than 80° to the axis.