Definition of radiation in physics

Summary

In physics, radiation is the emission or transmission of energy through space or a material medium in the form of waves or particles. It occurs naturally in many contexts (e.g., light and sound) and includes electromagnetic radiation (photons such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays), particle radiation (subatomic particles with non-zero rest energy such as alpha, beta, proton, and neutron radiation), acoustic radiation (ultrasound, sound, seismic waves), and gravitational radiation (gravitational waves). Radiation is commonly classified as ionizing or non-ionizing based on the energy carried by the radiated particles. Ionizing radiation has enough energy to ionize atoms and molecules—breaking chemical bonds—typically when it exceeds about 10 electron volts (eV). Non-ionizing radiation has lower energies that generally cannot ionize atoms, though it can still disrupt molecular bonds or cause effects like heating (from visible/infrared/microwave/radio energy) or skin damage (e.g., sunburn from ultraviolet). The boundaries between these categories are not perfectly sharp, and some effects overlap across frequencies.

Key Points

• 1

  Radiation in physics is the transfer of energy through space or a medium via waves or particles.

• 2

  Ionizing radiation carries sufficient energy to ionize atoms and break chemical bonds, increasing biological harm potential.

• 3

  Non-ionizing radiation generally cannot ionize atoms but can still cause biological effects such as heating or surface damage (e.g., UV causing sunburn).

• 4

  Radiation types include electromagnetic, particle, acoustic, and gravitational radiation.