X-ray Tube
✔ The x-ray tube, however, is a special type of vacuum tube that contains two electrodes:
1-the cathode
2-the anode.
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✔It is relatively large, perhaps 30 to 50
cm long and 20 cm in diameter.
✔The glass enclosure is made of Pyrex glass to enable it to withstand the tremendous heat generated.
✔The cathode is the negative side of the x-ray tube; it has two primary parts, a
filament and a focusing cup.
✔When the current through the filament is sufficiently high, the outer-shell electrons of the filament atoms are “boiled off” and ejected from the filament.
✔This phenomenon is known as thermionic emission.
✔ The x-ray tube current is adjusted by controlling the filament current.
Because;
a. At low filament current, there is no tube current because the filament does not get hot enough for thermionic emission.
b. When the filament current is high enough for thermionic emission, asmall increase in filament current results in a large increase in x-ray tube current.
c. This relationship between filament current and x-ray tube current depends on the tube voltage.
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