Principles of Radiography

Question 1

How does an xray machine produce radiation?

Answer 1

1. Electric passes from the mains BUT is too strong, so before it enters the cathode it is stepped down with a filament transformer
2. When the electrical current passes through the cathode it heats up and releases a cloud of electrons (the size of which is dictated by the mAs) known as thermionic emission.
3. In order for this to travel across to the anode at speed there needs to be a high electrical potential difference between the cathode (-ve) and anode (+ve).
4. This process takes up more electricity than the mains voltage can supply and so must be stepped up by a high tension transformer which is measured in Kilovolts (kV)
5. The cloud of electrons (-ve) is repelled by the cathode (-ve) and is attracted to the anode (+ve).
6. Electrons hit the target anode at speed to produce the x-ray photons via the release of their energy.
7. X-ray photons then form the primary beam and exit the tube head via the tube window.
8. Heat is a by product of this process therefore both the cathode and anode of made from tungsten alloy as is has a high atomic number (74) and a high melting point (3380C). This
   results in 99% of the energy released from the electrons when they hit the target being lost in heat.
9. This excess heat is absorbed by a copper block by conduction and travels via a copper stem to be cooled in an oil bath.