GB262906A - Improvements in and relating to x-ray tubes - Google Patents

Abstract

262,906. Dessauer, F. Nov. 16, 1925. R÷ntgen-ray tubes. - A low vacuum is employed in an X-ray tube, and the cathode and anti-cathode are freed from gas by heating or bombardment with cathode rays to such an extent that ionic discharges, which would normally occur at such a vacuum, are prevented and the tube is nonconductive except when the cathode is heated. The pressure may be between 6 x 10<-4> and 10<-2> mm. mercury. Positive ionization may be further prevented by surrounding the cathode by a non- conducting sleeve, which may be a tubular extension of the envelope, or an additional glass cylinder. The cathode may consist of a tungsten spiral 4, connected at one end to a surrounding tungsten cup 3. Separate transformers 7, 10 supply the heating and high-tension current respectively. A tube which may be used for demonstrating the phenomena involved comprises a small side bulb open to the main tube and fitted with two metal electrodes and a palladium tube, through which hydrogen can be introduced by a gas burner. These two auxiliary electrodes are not specially treated to free them from gas, and a discharge can be produced between them at a voltage corresponding to an air sparh-gap of ¢-1¢ inches, while no discharge occurs between the main electrodes until the cathode is heated. Alternatively, the side bulb may contain calomel or an amalgam, evolving vapour when heated; slight ionization may then occur between the main electrodes, but is inuocuous. Specification 228,592 is referred to.