Survey of the Sciences - Unit 5. Isotopes and Radiation

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Date: October 21, 2012 Class: Survey of the Sciences Subject: Unit 5. Isotopes and Radiation Radioactivity is the emission of energetic particles or waves from atoms. Natural radiation occurs when unstable nuclei transform to some other nucleus by emitting radiation. As they decay over varying lengths of time (from microseconds to hundreds of thousands of years), they emit energetic particles or waves. An isotope is a form of a chemical element whose atomic nucleus contains a specific number of neutron s, in addition to the number of proton s that uniquely defines the element. The nuclei of most atom s contain neutrons as well as protons. When unstable isotopes break down into new isotopes, they usually emit alpha, beta, or gamma radiation. ALPHA PARTICLES Alpha particles are the nuclei of helium atoms. This means they contain two protons and two neutrons. They are relatively large particles so they move slowly and do not penetrate materials very easily: they can be stopped by a sheet of paper. If they do collide with other particles they can cause ionization i.e. they can knock electrons out of atoms, leaving an ion behind. The alpha particles are relatively large and heavy. As a result, alpha rays are not very penetrating and are easily absorbed. A sheet of paper or a 3-cm layer of air is sufficient to stop them. The alpha particle emitter will not penetrate the outer layer of our skin, but is dangerous if inhaled or swallowed. BETA PARTICLES Beta rays are much lighter energy particles. The beta particle is an energetic electron given off by the nucleus of unstable isotopes to restore an energy balance. They leave the nucleus at a speed of 270,000 kilometers per second. They can be stopped, for instance, by an aluminum sheet a few millimeters thick or by 3 meters of air. The RS-500 can detect most energetic beta particles through the case.

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