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A radioactive substance is placed in a lead block. The radiations coming out are subjected to an electrostatic field. One type of radiations move towards negative plate, a second type moves towards positive plate and the third remains unaffected. Similarly when the radiations are subjected to magnetic field in a direction perpendicular to their direction of motion alpha particles moves one side, beta particle moves to the other side and gamma rays remains unaffected. This clearly shows that there are three types of radioactive radiations 1) alpha, 2) beta and 3) gamma.
Properties:
1. Each particle of alpha rays is nothing bur a Helium nucleus with mass number 4 and atomic number 2 [2He4]
2. These rays deflected by electric and magnetic fields showing that they are positively charged particle.
3. They affect photographic plates and cause fluorescence.
4. They produce strong ionisation when they pass through gases.
5. Alpha rays have small penetrating power.Even a piece of card-board can stop them.
6. Their velocities vary from 1/ 100 to 1/ 10 th of the velocity of light.
7. Alpha rays can produce artificial disintegration (i.e. induced radio-activity ) of nuclei.