Plot of number of neutrons   versus number of protons in stable nuclides

1. There exists a narrow band of neutron-to-proton ratios that make up stable nuclides. 2. The n/p ratio increases as the atomic number increases. 3. There are no stable nuclides with atomic numbers under 83. 4. The narrow band of stability is surrounded by much instability. 5. Nuclides that lie above the narrow band are neutron rich because they have too many neutrons. 6. Nuclides that lie below the narrow band are neutron poor because they have too few neutrons.

Neutron Rich

• A nuclide with more neutrons than the heaviest stable isotope of the element.
• Undergoes electron emission
• Converts a neutron into a proton, thereby increasing the atomic number.

Neutron Poor

• A nuclide with fewer neutrons than the lightest stable isotope of the element
• Two ways to adjust the n/p ratio if the atomic number is less than 83:
  1. Undergoes positron emission in lighter nuclides.

     

  2. Undergoes electron capture in heavier nuclides.

     

• Converts a proton into a neutron, thereby lowering the atomic number.
• If the atomic number is greater than 83:
  • Undergoes alpha decay.

    

Next:  "Binding Energy"