X ray tube

• What is the primary use of a stationary anode X-ray tube?


  It is primarily used in dental units.
• What are the two main components of an X-ray tube?


  The two main components are the insert and the shield.
• What material is the glass envelope of the X-ray tube made from?


  The glass envelope is made from borosilicate glass.
• Why must the glass envelope be a good electrical insulator?


  To prevent current from flowing through it when a potential difference is applied.
• What is the purpose of the re-entrant seals in the glass envelope?


  They allow for thermal expansion to prevent cracking.
• What happens over time to the inside of the glass envelope?


  A thin film of tungsten is deposited on the inside.
• What is the consequence of the tungsten film deposition inside the glass envelope?


  It may cause electrical breakdown within the tube.
• What is the function of the cathode in the X-ray tube?


  The cathode operates at a high negative potential and emits electrons.
• What materials are used to make the focusing cup in the cathode?


  The focusing cup is made of nickel or stainless steel.
• How does the negative bias on the focusing cup affect the electron beam?


  It squeezes the electrons together to form a narrow beam.
• Why is tungsten used for the filament in the cathode?


  Tungsten has a low thermionic work function and a high melting point.
• What is the significance of tungsten's low vapor pressure in the filament?


  It prevents the wire from becoming thin and reduces tungsten deposition on the glass.
• What is dual focus in the context of X-ray tubes?


  It refers to having two filaments side by side.
• How does the filament transformer contribute to electrical safety?


  It is contained in the same oil-filled tank as the high-tension transformer for insulation and heat dissipation.
• What is the effect of the anode angle on the focal spot size?


  The smaller the angle, the smaller the effective focal spot size.
• What is the composition of the anode in a stationary X-ray tube?


  The anode consists of a rectangular tungsten target embedded in a copper cylinder.
• What role does the copper cylinder play in the anode?


  It supports the target and acts as an electrical conductor.
• How does the anode contribute to heat dissipation?


  The copper cylinder conducts heat from the target, restricting its temperature rise.
• What is the thermal conductivity of copper?


  400 Wm^-1K^-1
• What is the purpose of the oil surrounding the remote end of the anode cylinder?


  It acts as an electrical insulator and converts heat to the outer housing.
• How does heat leave the cylinder during operation?

  Heat leaves by radiation across a vacuum to the glass envelope.
• Why is tungsten used as a target material in X-ray tubes?

  Tungsten has a high melting point and a high atomic number.
• What is the line focus principle in X-ray tubes?


  It results in an effective focus smaller than the real focus due to the anode angle.
• What are the advantages of the line focus principle?


  • The real focus can be longer than the effective focus.
  • Allows for high values of mA due to larger thermionic emission.
  • Minimizes temperature rise at the target.
  • Reduces geometric unsharpness by having a smaller effective focus.
• What is the minimum total filtration required at the tube port?


  1. 5 mm Al equivalent.
• What is the purpose of the X-ray tube housing?


  To provide electrical and radiation safety for staff and patients.
• What is the role of the metal casing surrounding the insert?


  It provides radiation protection and houses the oil for insulation and cooling.
• What happens to the oil in the housing when it is heated?

  It expands and may trip a microswitch to prevent further exposures.
• What is the sequence of heat loss from a stationary anode tube during exposure?


  1. Heat is deposited at the focal spot.
  2. Some heat is lost by radiation through the vacuum.
  3. Most heat is lost by conduction through the tungsten target.
  4. Heat sets up convection currents in the oil.
  5. Heat passes from the oil to the metal housing.
  6. Warm casing sets up convection currents in the air.
• What are the three basic principles of electrical safety in X-ray tubes?


  Insulation, earthing, and restricted access to live components.
• What is the purpose of the penumbra in X-ray imaging?


  It is the zone of partial shadow surrounding the X-ray shadow.
• How does the electron beam focusing work in X-ray tubes?


  The focusing cup directs electrons towards the central axis, reducing the focal spot size.
• What is the effect of the angulation of the target on the focal spot?


  The target appears foreshortened from the perspective of the central ray.
• What is the actual focal area in an X-ray tube?


  It is the rectangular area bombarded by electrons.
• What is the apparent focal area in an X-ray tube?


  It is the foreshortened view of the actual focal area from the perspective of the central ray.