Radioactivity & Astronomy

• Atom


  Positively charged nucleus and negatively charged electrons
• An atom is about 10-10 m in diameter. The nucleus is about 100,000 times smaller
• Nearly all the mass of the atom is in the nucleus
• Structure of an atom


  • Proton
  • Neutron
  • Electron
• Proton number (atomic or charge number)

  Number of protons in a nucleus
• Nucleon number (mass number)


  Total number of protons and neutrons in a nucleus
• Nuclide


  Type of nucleus
• Nuclide notation


  Symbol of the element X in the form ��

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• Isotopes


  Different forms of the same element with the same number of protons but different numbers of neutrons