High Transmission Coincidence Spectrometer with Good Resolution

Abstract

An electron-electron coincidence spectrometer is described. Magnetic lenses are used for the energy selection in each channel, and the coincidence counting efficiency is increased by using long lens spectrometers. At an effective transmission of 3%, relative half-widths of 1.3% (source diameter 0.2 cm) and 3.1% (source diameter 0.5 cm) were obtained. ``Triangular field'' focusing, introduced here, gives a favorable high luminosity in spite of small dimensions, distance between source and detector being only 25 cm in each half of the instrument. The focusing properties of this field form are discussed. Anthracene crystals cemented onto Lucite light guides serve as detectors, and it is shown that the light transmission efficiency of the guides can be considerably improved by machining them to a certain profile theoretically corresponding to 100% light collection. In practice efficiencies of 70−60% are obtained for Lucite light guides between 10 cm and 20 cm. The performance of the instrument is illustrated by some results obtained with coincidence measurements on the electron spectrum of Pb200.