SS: Deflection of radioactive particles

Deflection of radioactive particles in an electric field 

In the diagram above, a radioactive source is placed at one end of an electric field. The behaviour of the three types of emission in an electric field:

• The α-particles behave like positively charged particles and they are deflected towards negative plate in a parabolic path.
• The β-particles behave like negatively charged particles and are deflected towards positively charged plate. β-particles show much greater deflections than α-particles because of their lower mass.
• The γ-rays show no deflection in the electric field and travel in a straight line as they have no charge.

Deflection of radioactive particles in a magnetic field

The figure above illustrates the behaviour of the three types of emission in a magnetic field. (The magnetic field is coming out of the page as denoted by the dots.)

• The α-particles and β- particles are deflected in directions given by Fleming’s left hand rule.
• α-particles are positively charged. The direction of movement of α-particles can be considered as in the direction of conventional current flow (i.e. left to right). Therefore, the force on them must be towards the bottom.
• β-particles are negatively charged. The conventional current flow is in the opposite direction to the movement of β-particles (i.e. right to left). Therefore, the force on them must be towards the top.
• γ-rays are not affected by the magnetic field and they travel in a straight line.