chapter12 - CHAPTER 12 The Atomic Nucleus 12.1 12.2 12.3...

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n 12.1 Discovery of the Neutron n 12.2 Nuclear Properties n 12.3 The Deuteron n 12.4 Nuclear Forces n 12.5 Nuclear Stability n 12.6 Radioactive Decay n 12.7 Alpha, Beta, and Gamma Decay n 12.8 Radioactive Nuclides CHAPTER 12 The Atomic Nucleus It is said that Cockroft and Walton were interested in raising the voltage of their equipment, its reliability, and so on, more and more, as so often happens when you are involved with technical problems, and that eventually Rutherford lost patience and said, “If you don’t put a scintillation screen in and look for alpha particles by the end of the week, I’ll sack the lot of you.” And they went and found them (the first nuclear transmutations). - Sir Rudolf Peierls in Nuclear Physics in Retrospect
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12.1: Discovery of the Neutron n Rutherford proposed the atomic structure with the massive nucleus in 1911. n Scientists knew which particles compose the nucleus in 1932. n Reasons why electrons cannot exist within the nucleus: 1) Nuclear size The uncertainty principle puts a lower limit on its kinetic energy that is much larger that any kinetic energy observed for an electron emitted from nuclei. 2) Nuclear spin If a deuteron consists of protons and electrons, the deuteron must contain 2 protons and 1 electron. A nucleus composed of 3 fermions must result in a half-integral spin. But it has been measured to be 1.
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Discovery of the Neutron 3) Nuclear magnetic moment: The magnetic moment of an electron is over 1000 times larger than that of a proton. The measured nuclear magnetic moments are on the same order of magnitude as the proton’s, so an electron is not a part of the nucleus. n In 1930 the German physicists Bothe and Becker used a radioactive polonium source that emitted α particles. When these α particles bombarded beryllium, the radiation penetrated several centimeters of lead.
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n The nuclear charge is + e times the number ( Z ) of protons. n Hydrogen’s isotopes : q Deuterium : Heavy hydrogen. Has a neutron as well as a proton in its nucleus. q Tritium : Has two neutrons and one proton. n The nuclei of the deuterium and tritium atoms are called deuterons and tritons . n
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chapter12 - CHAPTER 12 The Atomic Nucleus 12.1 12.2 12.3...

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