Patent GB-679617-A (GB)
Title: Improvements in or relating to x-ray apparatus
IPC: G03B42/02
Filed: 1948-08-16
Abstract: 679,617. X-ray apparatus. WESTING- HOUSE ELECTRIC INTERNATIONAL CO. Aug. 16, 1948 [Sept. 27, 1947], No. 21595/48. Class 98 (i). In X-ray apparatus for displaying images of moving objects on a fluorescent screen having a long persistence of after-glow and of a type exhibiting a short time luminosity component as hereinafter defined, and comprising a source of X-rays, a fluorescent screen and an optical system through which light from the fluorescent screen passes, the source of X-rays is controlled to produce an X-ray pulse or pulses, the duration of which or each of which is not greater than the phosphorescent period (as hereinafter defined) of the short time luminosity component of the screen and the optical system includes means for permitting the light from the screen to be passed only during a time period or periods synchronized with the X-ray pulse or pulses. It is stated that certain fluorescent materials, notably fluorescent sulphides such as zinc sulphide, which give a high intensity of fluorescense, exhibit on stimulation an intensity of light which varies as if it comprised two components increasing exponentially with time. One component, defined as the short time luminosity component, increases much more quickly than the other, and the time after which it reaches 1/e of its theoretical maximum is defined as its phosphorescent period. The other component produces blurring effects in X-ray kinematography, which are to be eliminated. It is stated that the variation of intensity may also be regarded as comprising more than two components, and that the components need not be exponential in form. As shown, the X-ray tube 1 is connected in series with a gas-discharge tube 7 and a condenser 11 charged to a high potential by a conventional rectified current supply. The tube 7 is normally maintained non-conductive by a battery 8 which applies negative potential through a resistance to a trigger electrode. A camera 4 has a lens system between the elements of which a conductive disc 18 is rotated by a motor which may also drive mechanism for moving film intermittently through the camera. Disc 18 has diametrically opposite projectors 17 and apertures 24, 25, so arranged that at the moment when an aperture registers with the lens, a projection 17 wipes a brush 16, completing a circuit from a battery 15, brush 16, projection 17, through disc 18 to a brush 19 wiping the disc continuously, to the primary winding 14 of a transformer. The make-andbreak of this circuit produce pulses in the transformer secondary 13, and the positive-going pulse is applied, through condenser 12, to the trigger electrode. Tube 7 is thus rendered conductive and condenser 11 is discharged therethrough and through tube 1, producing a short pulse of X-rays which pass through a body 3 to form an image on a fluorescent screen 2. The pulse of X-rays may last from 1 to 100 microseconds, and the shutter may be open for the same period or for a slightly longer or short period, according to requirements. In an alternative arrangement, the gas-discharge tube is placed in the filament circuit of the X-ray tube. When the discharge tube is rendered conductive, a condenser discharges through the filament raising it to incandescence for a short period to permit X-ray emission. The film may be moved continuously through the camera 4, which is then provided with a tilting lens or mirror system. The disc shutter may be replaced by an electromagnetically-operated reciprocating shutter which may be operated in synchronism with the current pulses. The taking of the photographs may be synchronized with the A.C. supply frequency by driving disc 18 by a synchronous motor and using the alternating voltage to trigger the discharge tube. The image, instead of being photographed, may be viewed through an eyepiece.