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Mass defect
The difference in mass of a nucleus and its constituents, , is called mass defect and is given by
Alpha particle | Beta particle | Gamma particle |
It is a helium atom and contains two neutrons and two protons | It is an electron or a positron emitted by the decay of nucleus | It is an energetic photon or light wave. |
Heavier than beta and gamma particles | Much lighter than alpha particles | It is a wave unlike alpha and beta particles. |
Least penetrating energy. A sheet of paper or a 3-cm layer of air is sufficient to stop them. | They can be stopped, for instance, by an aluminium sheet a few millimetres thick or by 3 metres of air. | Highest penetrating energy.Gamma waves can be stopped by a thick or dense enough layer material, with high atomic number materials such as lead or depleted uranium being the most effective form of shielding. |