The existence of the three distinct types of radiations, alpha, beta and gamma rays can be easily found by the following experiment. A small amount of radium (R) is placed at the bottom of a small hole drilled in a lead block, which is kept in an evacuated chamber. A photographic plate is placed at a short distance above the lead block. A strong magnetic field is applied at right angles to the plane of the paper and acting inwards. Three distinct traces can be seen on the photographic plate when it is developed. The trace towards left is due to positively charged particles. They are named a-particles.The trace towards the right is due to negatively charged particles. They are named beta particles. The undeviated trace is due to neutral radiations which are called gamma rays. If an electric field is applied, the alpha rays are deflected towards the negative plate, beta rays towards the positive plate and gamma rays are not deflected.
