School of Physics Lecture Demonstration Manual

Na-7 X ray tubes

Published: Friday 17 March 2006 - Updated: Thursday 31 March 2011


To demonstrate various X ray tubes



Click on pictures to enlarge.

X Ray Tube Pic 4

X Ray Tube Pic 3

X Ray Tube Pic 2

X Ray Tube Pic 1


Various X ray tubes are available including Gas , Coolidge and rotating anode types.The original X ray tubes relied on evacuating tubes to low pressure. The electrons and positive ions are produced in the residual gas. Positive ions accelerated towards the cathode release electrons which on hitting the anode produce X rays. These early gas X ray tubes operated satisfactory only over a narrow pressure range.

In 1913 Coolidge overcame the limitations of these tubes with the invention of the vacuum tube. A filament heated by an electric current directly releases electrons by thermionic emission. The electrons accelerate to the anode and produce X rays. Due to the high temperatures attained by the release of the kinetic energy of the electrons on colliding with the anode, the anode has associated cooling fins. A modern X ray tube differs little from the original Coolidge tube. A minor modification is the rotating anode type that extends the life of the tube by presenting a new portion of the anode when required.

Safety notes

Sharps safety 


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