Radiography at high speed

Development of a cold-cathode X-ray tube makes it possible to make records on film of distortion inside objects opaque to visible light, thus supplementing high-speed photography THE interesting results attained by ultrahigh speed or flash photography are well known to newspaper and magazine readers everywhere. Distortion due to momentary strain can be shown in many familiar objects, such as golf balls and rapidly vibrating open relays. A new technique using X radiation instead of visible light makes it possible to record distortion or change in the interior of opaque objects as well as that visible on the outside. To make such radiographs at speeds of about one microsecond, enormous currents must be passed through the X-ray tube for that very short time interval. In the conventional hot-cathode X-ray tube, the available electron current is definitely limited by safe cathode temperature and space-charge effects. These limitations are avoided by the use of a cold-cathode X-ray tube recently developed in the Westinghouse lamp research laboratories at Bloomfield, N. J. In place of the conventional filamentary cathode, this tube employs a pair of cold electrodes G and H (figure 1). G is the true cathode and is so shaped and located with respect to its auxiliary electrode H that enormous potential gradients are built up when voltage is applied between these electrodes. Under the influence of these high gradients, a copious supply of electrons is obtained by cold emission from electrode G. Currents of from 1,000 to 2,000 amperes pass through the tube for periods of about one microsecond. The X-ray energy produced under these conditions is sufficient to produce radiographs of many objects in this short time interval, and consequently rapidly moving objects may be radiographed without blur caused by motion.