Radioactivity - The spontaneous disintegration of an unstable nuclide by a first-order rate law.

Nuclide - A particular combination of protons and neutrons.

• "Parent" nuclide - nuclide from which radioactive decay occurs to produce one or more "daughter" nuclides

Radioactive Particles

Name	Symbol	Charge	Penetration Limit
alpha () particles		+	skin, thin metal foil
beta () particles		-	thicker foil, plastic
gamma () rays		0	lead, concrete

Modes of Radioactive Decay

• Alpha Decay
  • Generally restricted to heavier elements. (Only a few elements with atomic numbers less than 83 emit alpha particles)

• Beta Decay
  1. Electron () emission
     • Electron is ejected from the nucleus, therefore the charge increases by 1.

       

  2. Electron capture
     • Electron is drawn into the nucleus, therefore the charge decreases by 1.

       

  3. Positron () emission
     • Positron - antimatter equivalent of an electron.
     • The charge of the daughter nuclide decreases by 1.

       

• Gamma Emission
  • Daughter nuclides resulting from alpha or beta decay are generally in an excited state.
  • Very shortly thereafter, the energy is emitted in the form of a gamma ray photon.
  • In some cases, the gamma decay is delayed, and a metastable nuclide is formed.
    • Metastable - short-lived intermediate between alpha or beta decay and gamma emission.

• Spontaneous Fission
  • When a parent nuclide splits into two smaller daughter nuclides.
  • Usually gives off neutrons simultaneously.
  • Spontaneous means happens on its own, but a spontaneous fission reaction can take a very long time.

Next:  "Neutron-Rich versus Neutron-Poor Nuclides"