Radioactivity was first discovered by Henry Becquerel in the year 1896. The natural phenomenon in which heavy nuclei disintegrates (decays) spontaneously with the emission of certain radiations is called as Natural Radioactivity. It is also known as radioactive decay.
Types of Radioactive Decay:
α – decay: The radioactive decay where a helium nucleus is emitted with positive charge is called as α – decay. In α – decay, the atomic number (A) of product (daughter) nucleus decreases by 2 and mass number (Z) decreases by 4 than that of the parent.
The α – decay can be written as,
β – decay: The radioactive decay where electrons or positrons are emitted is called as β – decay. In β – decay, the mass number (Z) of the product nucleus remains the same but its atomic number changes by 1 than that of the parent.
The β – decay can be written as,
γ – decay: The radioactive decay where high energy photons are emitted is called as γ – decay. The emission of γ – ray dischanges the nucleus i.e., no change in A or Z. After emission of α or β particle, the nucleus is in excited energy state. The excited nucleus returns to lower energy state or ground state by emitting γ – rays.
All radioactive nuclei emit either α –rays or β – rays, followed by the emission of γ – rays. α –rays and β – rays are never simultaneously emitted. During disintegration of radioactive material both energy and charge are conserved.