Nuclei having N/P = 1 (N = neutron, P = Proton) are the most stable. Any departure from this nucleon ratio induces nuclear instability. Nuclei with N/P > 1.5 becomes so unstable that they undergo spontaneous disintegration with the emission of Alpha, Beta, and Gamma rays producing new nuclei, and this transformation continued from nucleus to nucleus until a stable nucleus is formed. This transformation continued of nuclei does not depend upon the environmental conditions like temperature, pressure, or state of the radio element. Thus nuclear instability is the cause of radioactivity. Hence radioactivity is a nuclear phenomenon.
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