The attenuation length of photoelectrons in thin films of uranium

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Abstract
Films of uranium up to about 1000 Å thick were evaporated on to quartz substrates at pressures less than 5 × 10−10 Torr. The attenuation length L of photoelectrons in the films was estimated by comparing the photoelectric emission current when the film was illuminated from the vacuum side (i1) to that when the film was illuminated from the substrate side (i2). Theory indicates a linear relationship between log (i1/i2) and thickness, and this was confirmed by experiment for illumination with light of photon energies from 3.5 to 5.0 eV. The constants of the relationship yield values for L between 60 and 120 Å, the attenuation length decreasing with increasing photon energy. Measurements of the electrical conductivity of the films as a function of thickness yielded a value for the mean free path of the conduction electrons of about 290 Å. The results suggest that the principal energy‐loss mechanism for the excited electrons is one of electron‐electron scattering.