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Nuclear Physics 2

Nuclear Physics 2. Radiation Properties. Starter. Paper, skin. Few mm. Helium nucleus. 3 mm Aluminium . Less than 1 m. High speed electron. 2 cm lead. Infinite. EM radiation. Strictly speaking the lead attenuates the gamma radiation so that it is little above the background radiation.

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Nuclear Physics 2

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  1. Nuclear Physics 2 Radiation Properties Leeds City College

  2. Starter Paper, skin Few mm Helium nucleus 3 mm Aluminium Less than 1 m High speed electron 2 cm lead Infinite EM radiation Strictly speaking the lead attenuates the gamma radiation so that it is little above the background radiation. Leeds City College

  3. 1 0 A X 1 1 A Z + 1 0 -1 0 -1 0 0 0 0 X n p Y e e + + ne ne + + Q Q + + A – 4 Z – 2 4 2 AZ Q X Y He + + 29 13 29 14 0 -1 0 0 Al Si e + ne + Q + 228 90 224 88 4 2 Q Th Ra He + + Equations for Decay Alpha e.g. Beta e.g. Leeds City College

  4. Production of Alpha Particles They come from heavy elements of mass greater than 106 atomic mass units. In classical physics, the strong force balances the electro-magnetic force, so the alpha does not have the energy to get out. In quantum physics, there is a small chance that the alpha can get out by a process of quantum tunnelling. At this level we assume that all the energy is kinetic. Alpha particle energy is between 3 and 7 MeV Energy well Maximum energy available Escape route by quantum tunnelling Leeds City College

  5. Range of Alpha Particle Ref: Helmut Paul Leeds City College

  6. Path of Alpha in a Magnetic Field Use Fleming’s Left Hand Rule to determine the path. Leeds City College

  7. Beta Particles In beta minus decay: Joe Holdsworth Wikimedia commons Inductiveload Wikimedia commons Beta minus decay involves the change of a neutron to a proton via the W- boson. It happens in smaller nuclei that have an excess of neutrons. Leeds City College

  8. Energy in Beta • All energy is kinetic, as the beta is a high speed electron (no sub-structure). • The energy is precise within an isotope. • There is a variable sharing between the electron, electron antineutrino, and the nucleus itself. • Momentum is conserved. • We are only interested in the maximum energy level. Number of b particles Max kinetic energy = Q Energy Leeds City College

  9. Valley of Stability The black line shows the stable isotopes. Unstable nuclides are radioactive. If there is an excess of neutrons, beta minus decay happens. If there are too few neutrons, beta plus decay happens. The higher up the sides of the valley, the less stable the nuclide. Leeds City College

  10. Alpha and Beta in a Magnetic Field The magnetic field is going into the board. Which path does each particle follow? Alpha Source Gamma Beta Leeds City College

  11. Force on the Charge • We know: • Velocity = distance  time • Current = charge  time • F = BIl The t terms cancel out to give: F = B I l = Q I t l = v t Leeds City College

  12. Motion in a magnetic field B field going into the screen The force at 90 o acts as a centripetal force, keeping the electron in a circular path. Force always acts at 90 o Leeds City College

  13. Bear Trap Remember that the direction of the electrons’ movement is in the opposite direction to the conventional current. So if the electrons are going from left to right, the conventional current is going from right to left. When using Fleming’s Left Hand Rule, the current is conventional. Leeds City College

  14. Equation For centripetal force: The v on the left cancels to get rid of the v2 term on the right: For a charge in a magnetic field: Rearranging: We equate these to give: Leeds City College

  15. Valley of Stability Leeds City College

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