What are X Rays and How X Rays are Produced

What Are X-Rays?

X rays are a form of electromagnetic radiation having high energy and a wavelength range of 0.1nm to 10nm. Wilhelm Rӧntgen discovered this kind of radiation first and named it X rays as it wasn’t known at that time like the way we name unknown variables in mathematics.

X Rays in Electromagnetic Spectrum
X Rays Detailed diagram

How Are They Formed?

The electrons in an atom occupy different quantum states characterized by the quantum numbers such as the principal quantum number(n), orbital angular quantum number (l), magnetic quantum number (ml) and spin quantum number (ms). Energy primarily depends upon principal quantum number(n). Two electrons in the innermost orbit can be said to be in K-shell (n=1) and other electrons in the second orbit are said to be in L-shell (n=2). So, when an electron collides with the atom, the incident electron knocks out an electron from the innermost orbit or K-shell consequently creating a vacancy in the K-shell. So, now an electron from higher energy state jumps or makes transition to the K-shell. This transition of the higher energy electron to the lower energy electron creates a difference of energy ∆E which is converted to an X-ray photon. 

Cathode ray tube protoype
Cathode ray tube


Cathode ray tube comprises cathode filament, high voltage field, a vacuum chamber, anode or a target where the electron will collide, a lead shielding, and a filter.

Cathode Filament:

  • It’s a metal filament with high melting point.
  • It produces electrons.
  • When the filament gets heated, the electrons are boiled off which is called thermionic emission.
  • The rate of production is controlled by the filament current.
  • More the number of electrons per unit time, more X-rays per unit time.

High Voltage Field:

  • It helps accelerating the electrons with its high voltage supply between cathode and anode.
  • The electrons produced at the cathode are accelerated towards anode through it.

Vacuum Chamber:

  • It removes the stuff that obstruct the electrons on their way to anode as air molecules may obstruct the paths of the electrons.
  • So, the chamber is evacuated to a vacuum so that the electrons can reach the anode with maximum kinetic energy.


  • First the electrons collide with anode and undergo large deceleration.
  • The kinetic energy is converted to X-ray photon and heat energy.
  • The anode is rotated to give away all the heat energy.

Lead Shielding:

  • It contains stray electrons and also absorbs the radiation.


It absorbs low energy photons.

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