There are some combinations of neutrons and protons in nuclei of an element which are more stable than others.

Stable nuclei do not emit radiations or lose nuclear particles and energy but unstable ones lose electrons or protons or neutrons and emit electromagnetic radiations. It is the emission of these particles and energy as electromagnetic radiations which cause the nuclei of atom I to acquire a stable state. The acquisition of stable state is usually accompanied by change in the number of protons as well and the element transmitters or decays into another element. The following I types of radiations are given out when an element transmitters or decays into another element.

1. Emission of alpha-particles:

Emission of alpha-particles takes place in radio-active isotopes of heavy elements such as 92U238, 88Ra226 etc. Alpha-particles are nothing but Helium nuclei and their emission causes the number of protons and neutrons to change. The element will thus move a little lower down the period table, i.e., it will change into another element with lower atomic number.

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2. Emission of beta-particles:

It is electrons only which constitute beta-particles. Emission of beta-particles involves reduction in the neutrons but that of protons goes up (a neutron splits to produce an electron and a proton). Thus the element involved moves a little higher up in the periodic table, i.e., changes into another element with a higher atomic number.

3. Emission of high energy electromagnetic radiations:

These high energy electromagnetic radiations almost always appear when either alpha or beta particles are given out and transmutation of an atom is in progress. These rays, such as X-rays and gamma-rays have a very high penetrating power.