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AP Physics V.B Nuclear Physics
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31.1 Nuclear Structure
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Rutherford’s Scattering Experiment
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Mass and charge of... Protons Neutrons
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Symbolically... Atomic mass number (protons and neutrons) Atomic number (protons) Chemical symbol A = N + Z
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“OK, let’s just drop Z”
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Isotopes
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Atomic mass units
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Conversion of atomic mass units to energy
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31.2 The Strong Nuclear Force and Binding Energy
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Take carbon-12 for instance
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The total mass of a stable nucleus is always less than the sum of the masses of its protons and neutrons. Or, philosophically, “The sum of the parts is greater than the whole.”
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So where is the extra mass?
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Note: binding energy is not something a nucleus has. It is something is lacks. Binding energy is much larger than the energy required to eject an electron.
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Ex. Calculate the total binding energy for iron-56.
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Ex. Calculate the total binding energy for helium.
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Keeping it all together
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The strong nuclear force Approximately one-million times e-m forces Attractive between all nucleons Currently, there is no mathematical description Short range – falls to zero beyond the diameter of the nucleus
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Fig. 31.2 Note: up to approximately 30-40 protons N = Z. Beyond this stable nuclei contain more protons than neutrons. Why?
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For nuclei with more than 83 protons...
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p. 972: 10-13, 14, 07B7 10.9.279 EE -27 kg 12.225.1 MeV 14.1622 MeV 07B7 a.0.0232u b.3.46 EE -12 J c.8.66 EE 31 d.8.69 EE 9 kg
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31.4 Radioactivity
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Henri (you can call him “Henry”) Bequerel
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The Curies
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Three types of radioactivity
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1. Alpha decay – emits a He nucleus
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General form of alpha decay
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Converted energy of alpha decay Kinetic energy of the alpha particle Recoiling energy of the parent nucleus
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Ex. Find the energy released when uranium-232 decays to thorium 228.
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2. Beta Decay – the emission of an electron (not an orbital electron)
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“Whoa, dudes, how does that happen?”
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More complications – add the neutrino (and its evil cousin the anti-neutrino)
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Neon to fluorine and the positron
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General form for beta decay
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3. Gamma Decay – emission of a gamma ray because of a change in energy level in the nucleus
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General form for gamma decay *Indicates excited state
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