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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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nuclear physics

Nuclear Physics

The atom and its nucleus

discovery of the nuclear atom
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
rutherford geiger and marsden
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
geiger marsden rutherford experiment
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
rutherford model
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
bohr model
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
spectra
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
spectra1
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
nuclear structure
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
isotopes
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
forces within the nucleus
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
forces within the nucleus1
Forces within the nucleus
  • Weak nuclear force
    • Responsible for decay of a neutron into a proton
    • Called beta decay