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Lecture20_NP1

Lecture20_NP1 - Nuclear Nuclear Physics 1 1 Topics Topics...

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Nuclear Physics 1 1
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Topics z Composition of the Nucleus z Ground State Properties z Nuclear Structure z Binding energy z Nuclear Models z Summary 2
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Geiger, Marsden, Rutherford expt. z (Geiger, Marsden, 1906 - 1911) (interpreted by Rutherford, 1911) z get α particles from radioactive source z make “beam” of particles using “collimators” (lead plates with holes in them, holes aligned in straight line) z bombard foils of gold, silver, copper with beam z measure scattering angles of particles with scintillating screen (ZnS ) 3
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Geiger Marsden experiment: result z most particles only slightly deflected (i.e. by small angles), ut some by large angles en backward but some by large angles - even backward z measured angular distribution of scattered particles did not agree with expectations from Thomson model (only small angles expected), z but did agree with that expected from scattering on small, ense positively charged nucleus with diameter 0 4 dense positively charged nucleus with diameter < 10 -14 m, surrounded by electrons at 10 -10 m Ernest Rutherford 1871-1937 5
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Composition of the Composition of the Nucleus Nucleus -- -- 1 From the experiments of Geiger and Marsden in 1911, it became clear that most of the mass of an atom is contained within a nucleus of size f 0 ~ 1 fm (= 10 -15 m ). 932 the eutron as discovered by Chadwick In 1932 , the neutron was discovered by Chadwick, the positron by Anderson and the first nuclear reaction with protons was observed by Cockcroft and Walton. 6
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Composition of the Composition of the Nucleus Nucleus -- -- 2 A nucleus is a quantum system consisting of eutrons and protons held together by a rong neutrons and protons, held together by a strong nuclear force . A nucleus of a given species, called a nuclide , is defined by its atomic number Z , that is, by the number of protons it contains. N is the number of neutrons in the nucleus and A = N + Z is the mass number. For example, 15 O as A = 15 N =7andZ = 8 7 has A 15, N 7 and Z 8.
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Composition of the Composition of the Nucleus Nucleus -- -- 3 Neutrons and protons are referred to collectively ucleons 8 as nucleons .
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Ground State Ground State Properties Properties -- -- 1 Nuclei with the same atomic number, but which differ in mass number, e.g., 15 O and 16 O are called isotopes . l examples: deuterium, heavy hydrogen 2 D or 2 H; heavy water = D O (0.015% of natural water) 2 U- 235 (0.7% of natural U), U-238 (99.3% of natural U), If nuclei have the same neutron number N, e.g., 3 d th ll d t 13 C and 14 N they are called isotones . hose with the same mass number e g 14 and 9 Those with the same mass number, e.g., C and 14 N are called isobars .
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Ground State Ground State Properties Properties -- -- 2 Nuclear Sizes – The size of nuclei can be inferred in many ways. One way is to use mirror nuclides : those with Z and N numbers switched, for l example: 15 15 87 ON 8p + 7n 7p + 8n
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Lecture20_NP1 - Nuclear Nuclear Physics 1 1 Topics Topics...

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