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Chapter 24 Nuclear Reaction and Their Applications “24.1 Radioactive Decay and Nuclear Stability” Nuclei: plural of nucleus (many nucleuses) The great majority of nuclei are unstable. An unstable nucleus exhibits radioactivity: it spontaneously decays by emitting radiation. Protons (+) and neutrons (neutral), the elementary particles that make up the nucleus, are called nucleons. A nuclide is a nucleus with specific numbers of the two types of nucleons. Most elements occur in nature as a mixture of isotopes , atoms w/ the same # of protons of the element but diff. numbers of neutrons. Each isotope of an element is particular nuclide that we identify by its protons and neutrons. A Z X X is the symbol for the particle, A-mass # (top) is mass number (sum of protons and neutrons), Z-atomic # is charge of particle (# of protons). The number of neutrons (N) is mass # A - atomic # Z. N= A-Z nuclides can be written as element name followed by mass #, ex. Chlorine-35, or chlorine-37 Particle: atom, ion, or molecule When a nuclide of one element decays, it emits radiation, and under most circumstances, changes into a nuclide of a diff. element. Three natural types of radioactive emission are: - alpha particles  :  α are identical to helium-4 nuclei. - beta particles β are high-speed electrons. - gamma rays ɣ : are very high-energy photons (a quantum(indivisible amount) of electromagnetic radiation) When a nuclide decays, it forms a nuclide of lower energy, and the excess energy is carried off by the emitted radiation and the recoiling nucleus. The reactant nuclide (one that gets decayed) is called the parent , the product nuclide is the daughter . Key principle for balancing nuclear reactions: the total Z (charge, # of protons) and the total A (sum of protons and neutrons) of the reactants equal those of the products: Total A Total Z Reactants = Total A Total Z Products Types of Decay: 1. Alpha ( α ) decay: involves loss of an alpha particle from a nucleus. For each alpha particle emitted by the parent (reactant), A (atomic mass, protons + neutrons) decreases by 4 and Z (atomic mass, # of protons) decreases by 2 in the daughter (product). Every element beyond bismuth (Bi; Z=83) is radioactive and exhibits alpha decay. So, alpha decay is the most common means for a heavy, unstable nucleus to become more stable. Ex. Radium (Rn) undergoes alpha decay to yield radon (Rn; Z=86) : 226 88 Ra 222 86 Rn + 4 2    ( A: α 226 222+4 ; Z: 88 86+2) 2. Beta ( ) β decay: general class of decay that includes 3 types: β -  decay,  β +  emission, and electron capture.  β - decay  :  involves the ejection of a β  -   particle from the nucleus: a neutron is converted into a proton, which remains in the nucleus, and a β  -    particle is expelled immediately : 1 0 n 1 1 p + 0 -1                                   β 14 6 C 14 7 N + 0   -1    again, total A and Z of reactants equals products
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This note was uploaded on 11/14/2010 for the course CHEM 1A taught by Professor Okamura during the Fall '08 term at UC Riverside.

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