Radioactivity and Nuclear Processes

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CHAPTER 10 - Radioactivity and Nuclear Processes Composition of atomic nucleus - neutrons and protons Nuclides are nucleus of different isotopes, which is represented by the symbol [pic]X - X being symbol of the element. A is the mass number, which is the sum of number of protons & neutrons; Z is the atomic number, the number of protons, which also represents the nuclear charge. Number of neutrons = (A – Z). For example, the symbol of carbon-14 nuclide is [pic]C, which means a carbon-14 nuclide has 6 protons and 8 neutrons. The nuclide symbol of lead-206 is [pic]Pb. Radioactive Decay Nuclei with unsuitable compositions are unstable and they undergo spontaneous disintegration or nuclear decay. Nuclides that undergo spontaneous decay are said to be radioactive. Nuclear decay changes a radioactive nuclide into a stable one, which also change the identity of the nuclide. For example, when a carbon-14 nuclide decays by emitting a beta particle, it becomes nitrogen-14 (which is stable). [pic]C ( [pic]N + [pic]e Therefore, unlike a chemical reaction, nuclear reactions alter the identity of the atom. Types of Radioactive Decay Alpha Decays There are several different types of radioactive decay. One frequently observed decay process involves production of an alpha (α) particle, which is a helium nucleus and assigned the [pic]α. This is the common mode of decay for heavy radioactive nuclides (those with atomic number, Z > 83). When a nucleus loses an alpha particle its mass number (A) decreases by 4 units and the atomic number (Z) decreases by 2 units. The product of an alpha decay is a nuclide with two less protons and neutrons, respectively, than the original nuclide. For example, uranium-238 ([pic]U) and radium-226 ([pic]Ra) decay by alpha particle emission, which change them to thorium-234 and radon-222, respectively.

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