HONR228Q Notes section k:

  • The Shell Model of the Nucleus

    1. Nuclear structure

      1. Nuclear shells
        1. Nucleons occupy "quantum states" in nucleus as do atomic electrons in atom
        2. Nuclear states fill up with pairs of nucleons with opposite spin (Pauli exclusion principle)
      2. Proton/neutron differences
        1. Proton and neutron energy levels quantized separately
        2. Same neutron level more tightly bound due to Coulomb repulsion
        3. Stable nuclei have approximately same binding energy for last proton or last neutron
        4. Neutrons fill shells until binding energy slightly less than last proton
        5. Least tightly bound nucleon is generally a neutron
      3. Magic numbers
        1. Shells complete when "magic numbers" reached
        2. 2, 8, 20, 28, 50, 82, 126
        3. Magic numbers marked on Chart of Nuclides
        4. Experimental evidence for shells
          1. Graphs showing more detail and expanded scale of binding energies for final nucleon
      4. Stability of paired nucleons
        1. Generally paired neutrons or paired protons more stable
        2. Total of 264 stable nuclides now known
          #ZN
          157eveneven
          53evenodd
          50oddeven
          4oddodd

    2. Origin of nuclear spectra

      1. Sources of nuclear transitions
        1. Radioactive decay transitions
        2. Excitation by nuclear bombardment
      2. Transitions leading to spectra
        1. Particle spectra
          1. Radioactive decay transitions between different nuclides are quantized
          2. Nucleus emits a particle (alpha or beta), changing into a different nucleus
          3. Particle energy is discrete because all states are quantized
          4. Illustrate by energy level drawings
        2. Gamma-ray spectra
          1. Transitions of nucleons between energy states are quantized
          2. Transitions largely between states of last (least tightly bound) neutron
          3. Nucleon moves to lower state and emits a gamma-ray photon

    3. Examples of Nuclear Spectra

      1. Alpha particle spectrum:

        1. 241Am à 237Np + alpha + gamma

        2. Several alphas and gammas
        3. Maximum alpha energy about 5.5 MeV
        4. If alpha decay is to excited state, gamma-ray is then emitted
      2. Beta particle spectrum:

        1. 207Bi + beta(-) à 207Pb + gammas

        2. Several betas and gammas
      3. Gamma-ray spectra

        1. 137Cs à 137 Ba* + beta(-) + gamma

        2. 60Co à 60Ni* + beta(-) + 2 gammas

        3. 22Na à 22Ne* + beta(+) followed by beta(+) + beta(-) à 2 gammas

      4. Demonstrations of spectra
        1. DEMO P4-02: NUCLEAR SPECTRA
        2. ALPHA SPECTRUM OF Am241
        3. GAMMA SPECTRUM OF Cs137
        4. GAMMA SPECTRUM OF Co60
        5. GAMMA SPECTRUM OF Na22
      5. Nuclides charts - reference for spectra and transition charts:
        1. KAERI Web-based chart of the nuclides(BNL server)
        2. KAERI Web-based chart of the nuclides(Korean server)

    4. Applications of nuclear spectra

      1. Identification of radioactive materials
      2. Keying on specific gamma-rays in radon testing
      3. Keying on specific gamma-rays in medical tracer scans

    Back to "The Water Drop Model of the Nucleus"

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    please e-mail Dr. Richard Berg, reberg@physics.umd.edu,
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