Million-Volt X-Ray Tube

Abstract

A PAPER on a million-volt X-ray tube which has been installed and is in operation for treatment at St. Bartholomew's Hospital was read before the Institution of Electrical Engineers by Allibone, Bancroft and Innes at a meeting held on April 13. A description was given of the design, equipment, lay-out and operation of the unit. Briefly, it may be said that the tube embodies the principles of the all-metal X-ray tube designed by Dr. Allibone for lower voltages, and the elaboration set out in the present paper arises from the scale of voltages used. The X-ray tube consists of a steel tube 14 in. in diameter and 17 ft. long; the central portion of it, from which the X-ray beam emerges, traverses the treatment room and projects into each generator room. The generator rooms each house 500 kv. D.C. generators. The X-ray tube and thermionic rectifiers used in the D.C. generators are evacuated continuously by oil diffusion pumps, and the whole apparatus is readily demountable. Removable filament assemblies are fitted to the rectifiers and facilitate rapid replacement of filaments; a special cathode with six interchangeable filaments has been developed for the X-ray tube to avoid frequent admission of ait into the tube during filament replacements. The tube is now used continuously at 1000 kv. and has been operated experimentally at 1100 kv. Curves relating X-ray output with voltage and filtration by metallic filters are given, and a radiograph is included to illustrate the capabilities of the tube if applied to industrial radiography.