The Use of Three Long Rectangular Coils for Neutralization of the Earth's Magnetic Field in a Lens-Type Beta-Ray Spectrometer

Abstract

Accurate neutralization of the earth's magnetic field B_e over a long cylindrical region is necessary to extend the energy range of a magnetic‐lens spectrometer to electrons of very low energy. Axial conductors spaced 45° apart on the surface of a circular cylinder of radius a are used to approximate a cosθ distribution. The conductors at π/2 are missing since cosθ vanishes. There are 1/√2 as many conductors at ±π/4 and ±3π/4 as at 0 and π. In the plane transverse to the length of the cylinder, the radial variation of the compensating field is given approximately by the term B_e(r/a)⁶ cos6θ. Beta‐rays of a few kilovolts energy, which reach a maximum radius a/2, experience an average residual field of about 0.1 percent of B_e which produces a deflection of about 0.1 mm for a one‐meter spectrometer. The construction of the coils is described.