Abstract
An electron gun with an effective concentric-spheres electrode geometry has been used to investigate the energy distribution of electrons emitted by a space-charge-limited dispenser cathode at four different temperatures. A spherical monochromator is used to select different portions of the initial energy spectrum. Electrons so selected are scattered through 90° by an atomic beam of helium. The initial electron energy is inferred from the accelerating potential needed to attain the 19.3-eV helium resonance energy. Energy spectra so obtained are compared with computed spectra based on an initially half-Maxwellian distribution filtered by the space charge in front of the cathode. The form of this space charge is known from an exact solution of Poisson's equation in the spherical geometry of the gun. The only adjustable parameter in the computation is Richardson's constant which is given a value of A = 7 × 104 A/m2 (°K)2. The close agreement between the observed and computed energy spectra is in disagreement with observations of many other investigators. Reasons for this disagreement are suggested.
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