School of Physics Lecture Demonstration Manual

Ei-8 Magnetic deflection of Beta rays

Published: Tuesday 05 June 2007 - Updated: Tuesday 29 March 2011


To demonstrate that beta particles are charged particles electrons and that they may be deflected by a magnetic field



Click on pictures to enlarge.

Deflection pic 1

Deflection Pic 2

Deflection Pic 3


A strontium 90 source is placed below the poles of a strong horseshoe magnet. A lead aperture is used to ensure that beta particles are reasonably well collimated. With no magnet the detector produces maximum counts when in line with the source. Introducing the magnet requires the detector to be perpendicular to the source illustrating the deflection has been quite dramatic.

Safety notes

Electrical Safety 

Radiation Safety 


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