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

3. relativistic energy & relativistic momentum relativistic mass: relativistic energy: E = mc 2 relativistic momentum: p = mv energy – momentum relation:

4. attributes of selected particles proton 1.67262  10 -27 1.007276938.28e½ neutron 1.67493  10 -27 1.008665939.570½ electron 9.1094  10 -31 0.00054860.510999-e½ positron 9.1094  10 -31 0.00054860.510999e½ photon00000 neutrino0000½ mass kga.u. MeV/c 2 charge spin

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 m I = -I, …. I - the z component of the spin is

6. Nucleus size and shape Rutherford’s experiment Ze d m 2e Conclusion: where r 0 = 1.2 fm

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

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

9. Fission and Fusion 050100150200 250 1 2 3 4 5 6 7 8 9 mass number binding energy per nucleon (MeV) region of greatest stability Fission – heavy nuclei (A>60) split releasing energy Fusion – light nuclei (A<60) combine releasing energy

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

11. 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 N 0 – initial number of radioactive nuclei Activity: R 0 – initial activity units: (becquerel), 1Ci = 3.7 · 10 10 Bq (curie)

12. Half – life time The decay constant can be expressed in terms of time T ½, in which activity (the number of radioactive nuclei) decreases by a factor of two. t N N0N0 0