In pheesics, radiation is the emission or transmission o energy in the form o waves or pairticles throu space or throu a material medium.[1] This includes:

Illustration o the relative abilities o three different teeps o ionisin radiation tae penetrate solit maiter. Teepical alpha pairticles (α) are stappit bi a sheet of paper, while beta pairticles (β) are stappit bi an aluminum plate. Gamma radiation (γ) is stappit whan it penetrates lead. Note caveats in the text aboot this semplifee'd diagram.

Radiation is eften categorised as aither ionisin or non-ionisin dependin on the energy o the radiatit pairticles. Ionisin radiation cairies mair nor 10 eV, that is eneuch tae ionise atoms an molecules, an brak chemical bonds. This is an important distinction due tae the lairge difference in hairmfuness tae leevin organisms. A common soorce o ionisin radiation is radioactive materials that emit α, β, or γ radiation, conseestin o helium nuclei, electrons or positrons, an photons, respectively. Ither soorces include X-rays frae medical radiography examinations an muons, mesons, positrons, neutrons an ither pairticles that constitute the seicontar cosmic rays that are produced efter primar cosmic rays interact wi Yird's atmosphere.

Gamma rays, X-rays an the heicher energy range o ultraviolet licht constitute the ionisin pairt o the electromagnetic spectrum. The lawer-energy, langer-wavelenth pairt o the spectrum includin veesible licht, infrareid licht, microwaves, an radio waves is non-ionisin; its main effect whan interactin wi tishie is heatin. This teep o radiation anerly damages cells if the intensity is heich eneuch tae cause excessive heatin. Ultraviolet radiation haes some featurs o baith ionisin an non-ionisin radiation. While the pairt o the ultraviolet spectrum that penetrates the Earth's atmosphere is non-ionizing, this radiation does far more damage to many molecules in biological systems than can be accounted for by heatin effects, sunbirn bein a weel-kent example.

The wird radiation areeses frae the phenomenon o waves radiatin (i.e., traivelin ootwart in aw directions) frae a soorce. This aspect leads tae a seestem o meisurments an pheesical units that are applicable tae aw teeps o radiation. Acause sic radiation expands as it passes throu space, an as its energy is conserved (in vacuum). The intensity o aw teeps o radiation frae a pynt soorce follaes an inverse-square law in relation tae the distance frae its soorce. Lik ony ideal law, the inverse-square law approximates a meisurt radiation intensity tae the extent that the soorce approximates a geometric point.


  1. Weisstein, Eric W. "Radiation". Eric Weisstein's World of Physics. Wolfram Research. Retrieved 11 Januar 2014.