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Physics-30.24-Physics-Solids and Semiconductors
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Physics-29.23-Atoms-Molecules & nuclei
1. RADIOACTIVITY It was observed by Henri Becquerel in i896 that some minerals like pitchblende emit radiation spontaneously, and this radiation can blacken photographic plates if photographic plate is wrapped in light proof paper. He called this phenomenon radioactivity. It was observed that radioactivity was not affected by temperature, pressure or chemical combination, it could therefore be a property that was intrinsic to the atom-more specifically to its nucleus. Detailed studies of radioactivity resulted in the discovery that radiation emerging from radioactive substances were of three types : -rays, -rays and -rays. -rays were found to be positively charged, -rays (mostly) negatively charged, and - rays uncharged. Some of the properties of and – rays, are explain below: (i) Alpha Particles: An -particle is a helium nucleus, i.e. a helium atom which has lost two electrons. It has a mass about four times that of a hydrogen atom and carries a charge +2e. The velocity...
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