Chapter 44 - 44 Nuclear Structure CHAPTER OUTLINE 44.1 44.2...

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44 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 Nuclear Structure ANSWERS TO QUESTIONS Q44.1 Because of electrostatic repulsion between the positively- charged nucleus and the +2 e alpha particle. To drive the α - particle into the nucleus would require extremely high kinetic energy. Q44.2 There are 86 protons and 136 neutrons in the nucleus 86 222 Rn. For the atom to be neutral, there must be 86 electrons orbiting the nucleus—the same as the number of protons. Q44.3 All of these isotopes have the same number of protons in the nucleus. Neutral atoms have the same number of electrons. Isotopes only differ in the number of neutrons in the nucleus. 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 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. Q44.6 Nucleus Y will be more unstable. The nucleus with the higher binding energy requires more energy to be disassembled into its constituent parts. Q44.7 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. Q44.8 In the liquid-drop model the nucleus is modeled as a drop of liquid. The nucleus is treated as a whole to determine its binding energy and behavior. The shell model differs completely from the liquid-drop model, as it utilizes quantum states of the individual nucleons to describe the structure and behavior of the nucleus. Like the electrons that orbit the nucleus, each nucleon has a spin state to which the Pauli exclusion principle applies. Unlike the electrons, for protons and neutrons the spin and orbital motions are strongly coupled. Q44.9 The liquid drop model gives a simpler account of a nuclear fission reaction, including the energy released and the probable fission product nuclei. The shell model predicts magnetic moments by necessarily describing the spin and orbital angular momentum states of the nucleons. 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 specific transitions.
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This homework help was uploaded on 04/13/2008 for the course PHYS 211 taught by Professor Shannon during the Spring '08 term at MSU Bozeman.

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Chapter 44 - 44 Nuclear Structure CHAPTER OUTLINE 44.1 44.2...

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