The Work Function of Uranium

The average work functions of vacuum-deposited uranium films and of uranium foil have been measured by the Kelvin contact potential difference method, under ultra-high vacuum conditions. The reference surface was that of well-aged polycrystalline tungsten. A reproducible value of 3.203 ± 0.013 ev was found for the work function of the vacuum-deposited films. In the case of the foil, the work function increased continuously and monotonically with the duration of electron bombardment, eventually reaching a limiting value of 3.080 ± 0.005 ev after about thirty-three hours' bombardment. Reasons are put forward for believing that the surface of the foil may not be that of clean uranium, but of a patchwork of uranium and uranium monoxide.