lecture 29 - Chapter 29 Nuclear Physics Milestones in the...

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    Chapter 29 Nuclear Physics
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    Milestones in the Development of  Nuclear Physics 1896 – the birth of nuclear physics Becquerel discovered radioactivity in  uranium compounds Rutherford showed the radiation had  three types Alpha  (He nucleus) Beta (electrons) Gamma (high-energy photons)
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    More Milestones 1911 Rutherford, Geiger and Marsden  performed scattering experiments   Established the point mass nature of the  nucleus Nuclear force  was a new type of force 1919 Rutherford and coworkers first  observed nuclear reactions in which  naturally occurring alpha particles  bombarded nitrogen nuclei to produce  oxygen
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    Milestones, final 1932 Cockcroft and Walton first used  artificially accelerated protons to produce  nuclear reactions 1932 Chadwick discovered the neutron 1933 the Curies discovered artificial  radioactivity 1938 Hahn and Strassman discovered  nuclear fission 1942 Fermi and collaborators achieved the  first controlled nuclear fission reactor
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    Ernest Rutherford 1871 – 1937 Discovery of atoms  being broken apart Studied radioactivity Nobel prize in 1908
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    Some Properties of Nuclei All nuclei are composed of protons and neutrons Exception is ordinary hydrogen with just a proton The  atomic number , Z, equals the number of  protons in the nucleus The  neutron number , N, is the number of neutrons  in the nucleus The  mass number , A, is the number of nucleons in  the nucleus A = Z + N Nucleon is a generic term used to refer to either a proton  or a neutron The mass number is not the same as the mass
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    Symbolism Symbol: X is the chemical symbol of the element Example:   Mass number is 27 Atomic number is 13 Contains 13 protons Contains 14 (27 – 13) neutrons The Z may be omitted since the element  can be used to determine Z X A Z Al 27 13
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    More Properties The nuclei of all atoms of a particular  element must contain the same number  of protons They may contain varying numbers of  neutrons Isotopes  of an element have the same Z  but differing N and A values Example:  11 13 13 14 6 6 6 6 C C C C
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    Charge The proton has a single positive charge,  +e The electron has a single negative  charge, -e The neutron has no charge Makes it difficult to detect e = 1.602 177 33 x 10 -19  C
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    Mass It is convenient to use  unified mass units,  u,  to express masses 1 u = 1.660 559 x 10 -27  kg Based on definition that the mass of one atom of  C-12 is exactly 12 u Mass can also be expressed in MeV/c 2 From E R  = m c 2 1 u = 931.494 MeV/c 2
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lecture 29 - Chapter 29 Nuclear Physics Milestones in the...

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