Apparatus Drawings Project. Report Number 17. Small X-Ray Tube: Developed for the Undergraduate Physics Laboratories of the University of Washington

A small well-shielded high-vacuum molybdenum-anode x-ray tube designed for use as an ionizing source with a Millikan oil-drop apparatus is described. An accelerating potential of 28-kv peak provides a continuous x-ray spectrum with a short-wavelength cutoff of 0.436 A as well as the intense K, L, M, and N series of the characteristic line spectrum of molybdenum. The 28-kv accelerating potential, with a saturation current of 0.2–0.3 ma rms, ensures adequate ionization with conventional equipment, while still permitting the convenient installation of the massive external shielding necessary in a teaching laboratory. Information on essential safety precautions and construction procedures is given.