Photon appearance potential spectroscopy of thorium

Evaporated films of thorium on a tungsten substrate have been examined by photon appearance potential spectroscopy (PAPS) with incident electron energies in the range 80–1000 eV (O5 to N3 levels). For low coverage, the peaks corresponding to the O5, O4 and N7, N6 levels were immediately observed. As coverage was increased, these peaks increased slightly and the other O and N peaks appeared suddenly; the N3 was the last to appear. Peak shape and position were independent of coverage. After exposure to oxygen, the major peaks were not significantly shifted but new satellites of the O4, N7, and N6 peaks were observed.