Class25HO - Class 25 Radioactivity and Nuclear Energy...

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Class 25 Radioactivity and Nuclear Energy Physics 106 Fall 2011 Press CTRL-L to view as a slide show.
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Last Time Last time we discussed: I Problems with Distance and Time I Rest, Kinetic, and Total Energies I Creation and Annihilation of Particles
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Learning Outcomes Today we will discuss: I The Beginnings of Nuclear Physics I Nuclear Size and Shape I Radioactive Decay Processes I Half-lives I Nuclear Energy
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The Beginnings of Nuclear Physics
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Milestones in the Development of Nuclear Physics I 1896 - the birth of nuclear physics I Becquerel discovered radioactivity in uranium compounds I Rutherford showed the radiation had three types I Alpha I Beta I Gamma
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Milestones in the Development of Nuclear Physics I 1911 Rutherford discovered the nucleus I 1919 Rutherford observes nuclear reactions I 1932 Chadwick discovered the neutron I 1933 the Curies discovered artificial radioactivity I 1938 Hahn and Strassman discovered nuclear fission I 1942 Fermi achieved the first controlled nuclear fission reactor
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Properties of Nuclei
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Counting Particles in Nuclei I The atomic number , Z , equals the number of protons in the nucleus I The neutron number , N , is the number of neutrons in the nucleus I The mass number , A , is the number of nucleons in the nucleus
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Symbols I Symbol: A Z X I X is the chemical symbol of the element I Example: 27 13 Al I Mass number is 27 I Atomic number is 13 I Contains 13 protons I Contains 14 (27 -13) neutrons I The Z may be omitted since the element can be used to determine Z
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More Properties I All nuclei of a particular element have the same Z I Different isotopes have different N I For example, carbon has four natural isotopes: 11 6 C 12 6 C 13 6 C 14 6 C
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Mass I unified mass units, u I 1 u = 1 . 660559 × 10 - 27 kg I One atom of 12 C has a mass of exactly 12 u I Mass can also be expressed in MeV/c 2 I From E = mc 2 I 1 u = 931.494 MeV/c 2
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Masses of Atomic Particles Particle kg u MeV/c 2 Proton 1 . 6726 × 10 - 27 1.007276 938.28 Neutron 1 . 6750 × 10 - 27 1.008665 939.57 Electron 9 . 109 × 10 - 31 5 . 486 × 10 - 4 0.511
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The Size of the Nucleus I First estimated by Ernest Rutherford in 1911 by seeing how close an alpha particle could get to a nucleus: 1 2 mv 2 = k e × 2 e × Ze d d = k e 4 Ze 2 mv 2
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Size of the Nucleus I For gold, d = 32 fm I For silver, d = 20 fm I 1 fm = 10 - 15 m is usually called a fermi
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Size and Density I Most nuclei are approximately spherical I All nuclei have nearly the same density I Nuclei can be understood as a collection of hard spherical nucleons I Average radius is r = r 0 A 1 / 3 I r 0 = 1 . 2 fm
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Nuclear Stability I There are very large repulsive electrostatic forces between protons I The nuclei are stable because of the strong force
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Nuclear Stability I If a nucleus has too many protons, a proton can change to a neutron by β + decay I If a nucleus has too many neutrons, a neutron can change to a proton by β - decay
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I Light nuclei are most stable if N = Z I Heavy nuclei are most stable when N
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Class25HO - Class 25 Radioactivity and Nuclear Energy...

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