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Nuclear Physics

Nuclear Physics. The atom and its nucleus. Discovery of the nuclear atom. 1909-Geiger and Marsden, working under Rutherford Scattering of alpha particles shot at a thin gold foil Alpha particle 4x mass of H atom Alpha particles-emitted when unstable elements decay

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Nuclear Physics

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  1. Nuclear Physics The atom and its nucleus

  2. Discovery of the nuclear atom • 1909-Geiger and Marsden, working under Rutherford • Scattering of alpha particles shot at a thin gold foil • Alpha particle 4x mass of H atom • Alpha particles-emitted when unstable elements decay • Used radon – source of alpha particle

  3. Rutherford, Geiger, and Marsden • Found that sometimes alpha particles were detected at very large scattering angles • This couldn’t be understood in terms of the prevailing model • Thomson

  4. Geiger-Marsden-Rutherford experiment • Deflection indicative of enormous force of repulsion between alpha particle and carrier of positive charge of atom • Positive charge resided on a tiny object • Alpha particle could approach + charge at a small d, and the Coulomb force of repulsion, would be enormous

  5. Rutherford model • Massive, positively charged nucleus • Electrons orbited nucleus • Force keeping electrons in orbit • Electrical force between negative electron charge and positive nuclear charge • Couldn’t explain why matter is stable, i.e. why atoms exist

  6. Bohr model • Examined hydrogen • Realized electron could exist in certain specific states of definite energy, without radiating away energy • Electron lose energy when makes transition from one state to a lower • Emitted energy is difference between states • Evidence-emission and absorption spectra

  7. Spectra • Normal conditions-lowest energy level • Atoms excited  higher level • As soon as they do, transition back down to lower state • Energy allows wavelength of emitted light to be calculated

  8. Spectra • Emission spectrum  set of wavelengths of light emitted by the atoms of an element • Send a light of specific wavelength through an atom • Doesn’t correspond to any of the wavelengths • Light transmitted without absorption

  9. Nuclear Structure • Protons and neutrons • # of protons is Z (atomic number) • Protons + neutrons = mass (A) • Electric charge is Z IeI • # of neutrons N= A-Z • Nucleon • Proton or neutron

  10. Isotopes • Nuclei that have the same number of protons, but different number of neutrons • Same number of electrons • Identical chemical properties, different physical • Mass spectrometer

  11. Forces within the nucleus • Nucleons bound by nuclear force • Attractive force • Stronger than electrical force if separation between 2 nucleons is small • Larger separation-small force • Nuclear radius • R = 1.2 A1/3 x 10-15m • A is total number of p and n

  12. Forces within the nucleus • Weak nuclear force • Responsible for decay of a neutron into a proton • Called beta decay

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