What is radioactivity?

What is radioactivity?  Please explain in detail.

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Radioactivity occurs when the nucleus of certain unstable atoms (with an atomic mass greater than 83) or certain isotopes (with an atomic mass less than 83) disintegrates. This process releases a stream of particles called radiation. The radiation penetrates or is absorbed into other materials. There are three type of particle streams (or rays) that are found in radiation:

1) Alpha: composed of helium nuclei; low absorption and penetration; capable of changing other element's nuclei

2) Beta: composed of electrons; high speed and penetration; low mass; capable of changing other element's nuclei

3) Gamma: electromagnetic rays; high energy; short wavelengths; high penetrating power; does not change other element's nuclei

We are constantly being exposed to a certain amount of radioactivity (i.e. sun's rays, cosmic rays, etc.) every day and all we can do is limit our exposure to it. Some radioactivity is life-threatening, however, and exposure to it should be prevented at all costs.

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