BRAINCAKEX-ray Tubes
An X-ray tube is an evacuated glass tube containing a cathode and an anode.
• Cathode (heater filament): a current heats the filament and electrons are released by thermionic emission.
• High p.d.: tens of kilovolts (up to about 150 kV) between cathode and anode accelerates the electrons.
• Vacuum: electrons do not collide with gas molecules on the way.
• Target: usually tungsten, set into the anode, because it has a high melting point and a high proton number.
• Rotating anode and cooling oil: about 99% of the energy becomes heat, so the anode spins to spread the heat over a larger area of target and oil carries heat away.
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Key terms in this lesson
- thermionic emission
- The emission of electrons from the surface of a heated metal, used to produce free electrons in an X-ray tube.
More in Medical Imaging
- Production of X-rays
- X-ray Attenuation Mechanisms
- Photoelectric Effect, Compton Scattering and Pair Production
- Attenuation of X-rays
- Contrast Media
- CAT Scanning
- Medical Tracers
- Technetium-99m and Fluorine-18
All 20 lessons in Medical Imaging · All OCR A-level Physics topics