X-Ray Photoemission from Coated Surfaces.
Abstract
X-ray photoemission from the following types of coated and low-z surfaces was measured: dielectric films backed by a conductor, painted metal foils, and low-z conductors. Steady-state irradiation was provided by an x-ray tube operated at 60 and 100 kV. The total emission current from front and/or back surfaces was measured for photons incident at 0 deg and 60 deg. Surfaces studied included: Be, CH sub 2 graphite, Mylar, Teflon, glass, PVC, and Saran plus various coatings of low-z and high-z paints on aluminum. Low-energy secondary electrons, which contributed up to 30 percent of the total emission, were retarded with a biased grid. On a few higher-z dielectrics, buildup depressed the measured photoemission currents around zero bias. Photoemission yields increased approximately as the cube of an effective atomic number, and CH sub 2 had the lowest observed photoemission yield. The yield from beryllium was two to three times that of CH sub 2; this large yield is several times higher than expected for pure Be and is attributed to a thick oxide layer. Present measured values plus previously-measured values of photoemission from metals are compared with results obtained from the QUICKE2 computer code, and agreement within 20 percent was found for most materials. Photoemission from a copper foil coated with low-z varnish was also measured as a function of varnish thickness. The observed emission decreased approximately exponentially with coating thickness to a minimum value corresponding to emission from varnish only. A simple model was developed to estimate such photoemission from a high-z metal coated with a thin low-z layer.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 19, 1975
- Accession Number
- ADA020161
Entities
People
- Kenneth W. Paschen
- Melvin J. Bernstein
Organizations
- The Aerospace Corporation