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Elements Of X-Ray Tube

X-Ray tube is the machine where production of X-Ray is take place. The X-Ray tube is mainly consist of three things which is called the elements of X-Ray tube.

Elements Of X-Ray Tube  Focusing Cup

Elements Of X-Ray Tube

The X-Ray tube elements are:
  1. Cathode
  2. Anode
  3. Focusing Cup


Made of thin wire (0.2nm) tungsten wire because tungsten 
  • has high atomic number
  • It is a good thermionic emitter
  • It can be manufactured into a thin wire.
  • It has very high melting point  

Focusing Cup

Focusing Cup is a made up of molybdenum because 
  • High melting point

  • Poor thermionic emitter so electron aren't released to interfere with electron beam from filament

  • Negatively charged to focus the electron towards the anode and stop spatial speed.
Read : Production of X-Rays

How Focusing Cup help us in producing X-Rays?

The focusing cup (cathode block) surrounds the filament which shapes the electron beam width. it is use to focus the electron on a small area ( focal spot )in the anode. there are two ways by which the focusing cup is energised, namely biased and unbiased. 

In unbiased setup same voltage is applied to both focusing cup and filament. in this type the electron spread is wider and the focal spot width is larger.

In Biased X-Ray tubes,insulated focusing cup are used and it is given more negatively supply than the filament. this create a higher electric field around the electron reduce the electron spread and gives smaller focal point width. thus the focusing cup width determines the focal spot width and the filament length determines focal spot length. 


Elements Of X-Ray Tube
Image credit: Sprawls

Target material of tungsten for same reason as filament.
  • Rhenium added to tungsten to prevent cracking of anode at high temperature and usage

  • Set into an outside disk of molybdenum with stem.

  • Positively charged to attract electron.

  • Set an angle to direct X-Ray photons beam down towards the patient usual angle is 5-15 degree.

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