L10 - Chapter 10: Nuclear Physics Principles Motivation...

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Chapter 10: Nuclear Physics Principles – Motivation • We’ve seen that most of our electric energy is still obtained by burning fossil fuels in order to produce mechanical energy in steam engines • This technology is associated with detrimental local and global effects upon the environment such as 1. particulate matter and scrubber sludge storage 2. acid rain 3. contribution to global warming, etc. What are the alternatives to using the chemical energy of coal to spin the turbines? The most promising alternative is to use nuclear energy – in this chapter we’ll learn about the principles at work in a nuclear reactor The principles will help us pinpoint not only the mechanisms of energy extraction from atoms, but also the disadvantages of nuclear reactors, such as 1. the radioactive waste storage 2. safety 3. radon accumulations, etc 10.1
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Nuclear Structure – Protons, neutrons. Classification • Unlike the energy employed by fossil fuel power plants, obtained by splitting molecules bound together by electric forces , energy used in nuclear reactors is released by splitting atomic nuclei bound together by strong nuclear forces The atomic nuclei contain nucleons : electrically positive protons and electrically neutral neutrons which are just slightly more massive than protons but about 2000 times heavier than electrons 10.2 e p + Ex : The simplest and most abundant atom in nature is hydrogen which has one proton orbited by one electron. Hydrogen has isotopes: deuterium and tritium • Elementary chemical substances are characterized by the number of nucleons called mass number A given by the number of protons Z and neutrons N • It is customary to denote elements indicating the atomic mass: • The same elements may have several isotopes: elements with the same Z but different A due to a different N A X e p + n 0 e p + 2 n 0 Hydrogen Deuterium Tritium 1 H 2 H 3 H Ex : a) The most abundant isotope of carbon (6 protons) is 12 C, b) the most abundant oxygen (8 protons) is 16 O
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Nuclear energy – Nucleons • The strong nuclear forces binding the nucleons together are 1. much stronger than electric forces such that the energies associated with the nucleus are millions of times larger than those of electric systems 2. very short range compared with electric forces: the strong forces act significantly only within the size of a nucleus, which is about 1/100,000 the size of an electron orbit The energies involved in the description of nuclear processes are typically expressed in electronvolts (eV): 1 eV = 1.6 × 10 –19 joules 10.2 Ex : The net energy (kinetic and potential) of an electron on the orbit is about 10 eV while the net energy of a proton in the nucleus is about 50,000,000 eV – about 5 million times higher The energy of the nucleons in a nucleus is quantized : this means that a nucleon absorbs and releases energy only in discrete portions Ex : The situation can be compared with the exchange of gravitational energy by a mass rolling
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L10 - Chapter 10: Nuclear Physics Principles Motivation...

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