A New Hot Cathode Tube with Rotating Anode

For his radiographic tubes, the radiologist requires the smallest possible focal spot and the biggest possible output. By this means, he obtains the sharpest definition in the minimum exposure time. For every size of focus, however, Nature only permits a certain maximum load. This is dependent upon the area of the focal surface; the duration of the load and also the construction of the anode. A load of 200 watts per square mm. of focal area for a period of one second is the maximum permissible for a correctly designed anode of tungsten and copper. Any higher load will inevitably result in evaporation or even melting of the anode. Increasing the load capacity by enlarging the focal spot does not result in any real advantage as in order to preserve the same sharpness of definition a larger focus entails the use of a greater focus-film distance. To minimise the exposure time this in turn means a relatively higher load. It is evident, therefore, that progress is only possible by making the anode moveable, and this in such a way that the focal spot itself remains stationary, as for instance, by rotation of the anode. The idea of a moveable anode is by no means new and dates as far back as the year 1897. In “La Revue Scientifique et Industrielle de l'Annee 1898-99” we find that J. L. Breton describes a tube with an anode which is capable of rotation during the load.