The
diagram shows how alpha, beta and gamma radiation would be deflected by a magnetic field
acting perpendicular to the path of the particles.
Alpha particles are deflected a little
because of their large mass while beta particles are deflected much more because they are nearly
two thousand times lighter. They have a negative charge while alpha particles are positive and so
they are deflected in the opposite direction.
Notice that the gamma rays are not deflected
at all – this is because they have no charge.
In the diagram the magnetic field acts into the
plane of the paper.