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SM_chapter44 - 44 Nuclear Structure CHAPTER OUTLINE 44.1...

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44 Nuclear Structure CHAPTER OUTLINE 44.1 Some Properties of Nuclei 44.2 Nuclear Binding Energy 44.3 Nuclear Models 44.4 Radioactivity 44.5 The Decay Processes 44.6 Natural Radioactivity 44.7 Nuclear Reactions 44.8 Nuclear Magnetic Resonance and Magnetic Resonance Imagining ANSWERS TO QUESTIONS Q44.1 Because of electrostatic repulsion between the positively-charged nucleus and the + 2 e alpha particle. To drive the a -particle into the nucleus would require extremely high kinetic energy. *Q44.2 (a) X has a mass number less by 2 than the others. The ranking is W = Y = Z > X. (b) Y has a greater atomic number, because a neutron in the parent nucleus has turned into a proton. X has an atomic number less by two than W, so the ranking is Y > W = Z > X. (c) Y has one fewer neutron compared to the parent nucleus W, and X has two fewer neutrons than W. The ranking is W = Z > > X. Q44.3 The nuclear force favors the formation of neutron-proton pairs, so a stable nucleus cannot be too far away from having equal numbers of protons and neutrons. This effect sets the upper boundary of the zone of stability on the neutron-proton diagram. All of the protons repel one another electrically, so a stable nucleus cannot have too many protons. This effect sets the lower boundary of the zone of stability. Q44.4 Nuclei with more nucleons than bismuth-209 are unstable because the electrical repulsion forces among all of the protons is stronger than the nuclear attractive force between nucleons. Q44.5 Nucleus Y will be more unstable. The nucleus with the higher binding energy requires more energy to be disassembled into its constituent parts. Q44.6 Extra neutrons are required to overcome the increasing electrostatic repulsion of the protons. The neutrons participate in the net attractive effect of the nuclear force, but feel no Coulomb repulsion. *Q44.7 (i) Answer (a). The liquid drop model gives a simpler account of a nuclear F ssion reaction, including the energy released and the probable F ssion product nuclei. (ii) Answer (b). The shell model predicts magnetic moments by necessarily describing the spin and orbital angular momentum states of the nucleons. (iii) Answer (b). Again, the shell model wins when it comes to predicting the spectrum of an excited nucleus, as the quantum model allows only quantized energy states, and thus only speciF c transitions. 541
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542 Chapter 44 Q44.8 The statement is false. Both patterns show monotonic decrease over time, but with very different shapes. For radioactive decay, maximum activity occurs at time zero. Cohorts of people now living will be dying most rapidly perhaps forty years from now. Everyone now living will be dead within less than two centuries, while the mathematical model of radioactive decay tails off exponentially forever. A radioactive nucleus never gets old. It has constant probability of decay however long it has existed.
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SM_chapter44 - 44 Nuclear Structure CHAPTER OUTLINE 44.1...

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