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Brief History of Nuclear Physics

Brief History of Nuclear Physics. 1896 - Henri Becquerel (1852-1908) discovered radioactivity. 1911 - Ernest Rutherford (1871-1937), Hanz Geiger (1882-1945) and Ernest Marsden (1888-1970) conducted scattering of alpha particles on nuclei.

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Brief History of Nuclear Physics

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  1. Brief History of Nuclear Physics 1896 - Henri Becquerel (1852-1908) discovered radioactivity 1911 - Ernest Rutherford (1871-1937), Hanz Geiger (1882-1945) and Ernest Marsden (1888-1970) conducted scattering of alpha particles on nuclei 1930 - John D. Cocroft (1897-1967) and Ernest T.S. Walton (1903-1995) conducted the first artificial nuclear reaction 1932 - James Chadwick (1891-1974) discovered the neutron 1933 - Frederick Joliot (1900-1958) and Irene Joliot-Curie (1897-1956) synthesized artificial elements 1938 - discovery of nuclear fission by Otto Hahn (1879-1968) and Fritz Strassman (1902-1980) 1942 - Enrico Fermi (1901-1954) builds a fission reactor

  2. + + 4 He + 2 + + + Properties of nuclei Mass Number A - number of nuclei - number of protons (charge, element) Atomic Number Z Neutron Number N - number of neutrons A X A nucleus is represented by symbol: Z Elements with different numbers of neutrons are called isotopes.

  3. E = mc2 p = mv relativistic energy & relativistic momentum relativistic mass: relativistic energy: relativistic momentum: energy – momentum relation:

  4. mass charge spin MeV/c2 kg a.u. attributes of selected particles

  5. the spin Spin – angular momentum like quantity responsible for the magnetic moment of particles. z quantum numbers: • spin quantum number I - the magnitude of the spin is • magnetic quantum number mI = -I, …. I - the z component of the spin is

  6. Conclusion: where r0 = 1.2 fm Nucleus size and shape Rutherford’s experiment m Ze 2e d

  7. Nuclear Stability Coulomb interaction - repulsive Nuclear interaction - attractive line of stability magic numbers (very stable nuclei): Z, N = 2, 8, 20, …

  8. Binding Energy The total (relativistic) energy of a nucleus is always less than the combined energy of the separated nucleons. The difference Eb (MeV) = ( Zmp + Zmn - MA ) · 931.491 MeV/a.u. is called the binding energy of the nucleus. Example (alpha particle): Eb= (2 · 1.0073au + 2 · 1.0087au – 4.0026au) · 931.491 MeV/au  27.4 MeV

  9. region of greatest stability 9 8 7 6 binding energy per nucleon (MeV) 5 4 3 2 1 250 0 50 100 150 200 mass number Fission and Fusion Fission – heavy nuclei (A>60) split releasing energy Fusion – light nuclei (A<60) combine releasing energy

  10. + - positrons radioactive source  - alpha particles  - high energy photons - - electrons Radioactivity - spontaneous emission of radiation resulting from disintegration (decay) of unstable nuclei. Types of radioactive decay: lead shield photographic plate

  11. (becquerel), Activity – the decay rate The number of disintegrated nuclei in a unit time is proportional to the number of radioactive nuclei in the source.  – the decay constant Hence N0 – initial number of radioactive nuclei Activity: R0 – initial activity units: 1Ci = 3.7 · 1010 Bq (curie)

  12. N N0 0 Half – life time The decay constant can be expressed in terms of time T½, in which activity (the number of radioactive nuclei) decreases by a factor of two. t

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