SOME THERMIONIC PROPERTIES OF BARIUM FILMS ADSORBED ON TUNGSTEN

Abstract

An investigation has been made of some thermionic properties of a barium film adsorbed on tungsten for various values of θ, the fraction of the surface covered with barium. The experimental tube was so constructed that the measurements could be made on a small area of the filament in order that errors due to lead losses, non-uniformities, and voltage drop along the filament might be minimized. An electrometer vacuum tube was used to measure the electron currents. The experimental results obtained by Eglin were confirmed, i.e. the thermionic activity of the composite surface was found to increase with θ until an optimum value was reached after which further deposit of barium caused the activity to decrease. As a result of prolonged deposition, a steady value of the activity was reached which did not change appreciably or regularly with further deposition. The change in C.D.P. was found to be directly proportional to the change in Tθ, the absolute temperature of the filament required to give an arbitrarily fixed value of electron emission. It is significant that the factor of proportionality for all values of the activity higher than the steady value reached after prolonged deposition was found to be different than that obtained for the values which were lower. The distribution of velocities of the emitted electrons was found to be Maxwellian for all values of θ. The construction of the experimental tube was found to be unsuitable for studying the effect of field intensity on the activity. Thus the results obtained pertaining to this effect are of little significance.