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Radiation, as used in physics, is energy in the form of waves or moving subatomic particles. Radiation can be classified as ionizing or non-ionizing radiation, depending on its effect on atomic matter. The most common use of the word "radiation" refers to ionizing radiation. Ionizing radiation has enough energy to ionize atoms or molecules while non-ionizing radiation does not. Radioactive material is a physical material that emits ionizing radiation.

This shows three different types of radiation and their penetration levels

• Electromagnetic radiation: (Energy in the form of electromagnetic waves or photons.)
  • Non-ionizing
    • Thermal radiation (heat radiation)
    • Radio waves
    • Microwave radiation, as used in microwave ovens
    • Infrared radiation (IR), produced by heat
    • Visible light light that is visible to the naked eye
    • Ultraviolet radiation (UV) is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays.
  • Ionizing
    • X-rays, used in radiography for medical diagnosis
    • Gamma radiation, usually emitted by radioactive atoms
• Particle radiation: (Energy in the form of moving subatomic particles.)
  • Alpha radiation, composed of the nuclei of helium-4 atoms
  • Beta radiation, consisting of energetic electrons or positrons
  • Neutron radiation, consisting of neutrons

The effect of magnetic and electric fields on these particles/rays:

• Positively charged alpha particles are deflected by both magnetic and electric fields.
• Negatively charged beta particles are also deflected by both types of fields, but in the opposite direction from alpha particles.
• Neutrons and electromagnetic radiation have no charge, and are unaffected by electromagnetic fields.

• Background radiation, which actually refers to the background ionizing radiation
• Black hole
• Cosmic microwave background radiation, 3°K blackbody radiation that fills the Universe
• Radiant energy, radiation emitted by a source into the surrounding environment.
• Radiation damage - adverse effects on materials and devices
• Radiation hormesis - dosage threshold damage theory
• Radiation poisoning - adverse effects on life forms
• Radiation hardening - making devices resistant to failure in high radiation environments
• Radioactive contamination
• Radioactive decay
• Hawking radiation
• Cherenkov radiation
• Cyclotron radiation
• Synchrotron radiation
• Radiation reaction