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Nuclear Physics

Nuclear Physics. Nuclear Structure. Nucleus – consists of nucleons (neutrons and protons) Atomic Number Z  number of protons Atomic Mass Number A  nucleon number  total number of neutrons and protons. Atomic Radius. r = (1.2 x 10 -15 m) A 1/3 r  radius

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Nuclear Physics

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  1. Nuclear Physics

  2. Nuclear Structure • Nucleus – consists of nucleons (neutrons and protons) • Atomic Number Z  number of protons • Atomic Mass Number A  nucleon number  total number of neutrons and protons

  3. Atomic Radius • r = (1.2 x 10 -15 m) A 1/3 r  radius A  atomic mass number

  4. Strong Nuclear Force • One of three fundamental forces that have been discovered (others  gravitational force, electroweak force) • Almost independent of electric charge • Nearly the same nuclear force of attraction exists between 2 protons, 2 neutrons, or between a proton and a neutron.

  5. Strong Nuclear Force • Range  short; very strong when nucleons are as close as 10-15 m  zero at larger distances • This limited range prevents extra neutrons from balancing longer range electric repulsions of extra protons and atoms become unstable • Bismuth  largest stable nucleus

  6. Radioactivity • All nuclei above bismuth , Z > 83, will have unstable nuclei and spontaneously break apart or rearrange structure of internal structure • This spontaneous disintegration or rearrangement is radioactivity

  7. Nuclear Binding Energy • The required energy to break a nucleus apart • DE = (Dm)c2 DE  binding energy Dm  mass defect of the nucleus (the difference in mass of the nucleus and the individual masses of the separated protons and neutrons) c  speed of light

  8. Radioactive Decay • When unstable or radioactive nuclei disintegrate spontaneously particles or high-energy photons are released • These particles and photons are called rays • There are three kinds of rays produced by naturally occurring radioactivity  a, b & g

  9. a Decay • When a nucleus decays and emits a rays • a rays  ray of positively charged particles; He+2 nuclei  42He • AZP  A-4Z-2D + 42He P  Parent D  Daughter

  10. a Decay • Energy released = difference in beginning and ending total atomic mass units • 1 amu or u = 931.5 MeV • Since the parent and daughter nuclei are different this is a process called transmutation

  11. b Decay • b rays consist of negatively charged particles • b– particles  electrons 0-1e • b- decay AZP  AZ+1D + 0-1e • b+ decay  AZP  AZ-1D + 01e (positron) • Use masses from Periodic Table to determine energy release

  12. g Decay • The emission of high energy photons when a nucleus changes from an exited energy state(*) to a lower energy state • Does not cause a transmutation • AZP*  AZP + g

  13. The Neutrino • Another particle emitted during b decay • Accounts for the energy missing from the KEb after emission • Verified experimentally in 1956 • Has zero electric charge • Interacts weakly with matter • Has mass, a fraction of an electron’s, and travel at less than the speed of light

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