X ray Coolidge tube:
X-rays are produced when fast moving electrons are suddenly stopped by a solid target. A Coolidge tube is shown in. Fig. 1.1(x rays tube diagram). The tube is exhausted to the best possible vacuum of the order of 10-5 mm of mercury. The cathode includes of a tungsten filament (F) heated by a low tension battery. Thermionic electrons emitted by the filament are accelerated tow-ards the target (T) by a high P.D. maintained between F and T. The filament is placed inside a metal cup G to focus the electrons directly to the target. The target needed to be cooled to eliminate the heat generated in it by way of continuous electron-bombardment. x - rays The usual method is to mount the target material on a hollow Fig. 5.1 copper tube through which cold water is continuously circulated. The target is made of a metal like tungsten or molybdenum having a high melting point and a excessive (high) atomic number. Metals with excessive ( high) atomic number give more extreme (energetic) and intense X-rays when used as targets.
Control of intensity and quality
In the Coolidge tube, the intensity and frequency of X-rays can be easily controlled.
(1) The intensity of X-rays depends at the number of electrons striking the target per sec(second). The number of electrons given out by the filament is proportional to its temperature, which could be adjusted by varying the current in the filament circuit. Therefore, the intensity of X-rays varies the filament current.
(2) The frequency of X-rays emitted depends on the voltage between the cathode and the anode (target).
This is Duane-Hunt law.
X-rays are electromagnetic waves of short wavelengths in the range of 1 nm to 0.05 nm. The longer wavelength end of the spectrum is known as the "soft X-rays" and the shorter wavelength end is referred to as "hard X-rays."
