Normal Energy Distribution of Photoelectrons from Sodium and Gallium

A new experimental method for the determination of the normal energy distribution of photoelectrons is outlined. The method involves separation of the electrodes by a large distance. The electrons are constrained to move along the axis of the phototube by applying a uniform axial magnetic field. The energy distribution is determined by measuring the photoelectric current as a function of retarding voltage between the emitter and the collector. The theoretical justification for this method is worked out. A phototube was made applying the above principles to measurements on liquid metal gallium. Another phototube was made for use with condensed surfaces of sodium. This tube was designed for extremely high vacuum use. Improvements in the photocurrent measuring apparatus and in vacuum technique were made. The monochromators were used in a way similar to that described by Overhage. The sodium was also handled in the manner developed by him. The uniformity of the magnetic field was checked and the currents in the coils adjusted to the most favorable value. The results for gallium showed departures from theory but internal consistency similar to that observed by Overhage. The results for sodium show excellent agreement with the Fowler Theory, indicating a very simple form for the transmission coefficient of the surface potential barrier. Measurements of h/e were possible from the data for sodium.