A Geiger counter with post-acceleration

Abstract

A Geiger counter with post-acceleration has been constructed for use with the Vanderbilt iron-free spectrometer. Electrons focused on the spectrometer exit slit are accelerated by an electric field before penetrating the counter window. The accelerating potential is variable from 0 to 8.5 kV. A variable decelerating potential (0 to 300 V), positioned in front of the accelerating field, rejects very low energy electrons, reducing the background. With the accelerating potential, electrons with initial energies of less than 1 keV can be detected with ∼ 100% efficiency with counter windows thick enough ( > 30 μg/cm 2) to maintain reasonable counter pressures (4 cm Hg) without leaking or breaking. Electrons with initial energies of 0.1 keV have been measured with window transmissions of 95%.