Alpha Rays

1. Nature: The direction in which these rays get deflected in an electric and magnetic field indicates that this rays are positive charged rays. They carry two unit of positive charge and 4 units of mass so on their removal the atomic number decreases by 2 unit and the mass number decreases by 4 unit. They are the helium nucleus.

2. Velocity: The velocity of alpha rays is found to be 10% that of light. The exact velocity depends upon the nature of source.

3. Ionizing Power: These rays ionize the gas through which they pass. The ionization takes place due to the knock out of the electrons from the molecules of the gas when the highly energetic heavy alpha particles strike these molecules.

4. Penetrating Power: Since alpha particles are heavy and comparatively slow moving, their penetrating power is less. For example, these rays can be stopped by an aluminum foil of 0.1 mm thickness.

5. Effect of Photographic plate and zinc sulphide screen: These rays affect the photographic plate just as ordinary light. When these rays fall on the screen coated with zinc sulphide, they produce luminosity. This phenomenon is known as fluorescence and substance like zinc sulphide which shows this phenomenon are known as fluorescent substances.