radiation
Meaning of radiation: Everyday exposure is unavoidable and mostly natural; what medicine controls is the far smaller share delivered deliberately, aimed and measured.
Definition of radiation
Radiation is energy that travels through space as waves or as moving particles. It comes from natural sources such as cosmic rays and radon gas in soil and rock, and from manufactured sources used in medicine and industry. The critical division is between ionizing radiation, energetic enough to strip electrons from atoms and damage DNA, and non-ionizing radiation, which is not.
How radiation is built
- radi/o Combining form · Latin x-ray, radiation
- -ion, -ation Suffix · Latin process, action, or its result
A medical term is read from its ending backwards: the suffix first, then the prefix, then the root. See all 223 word parts.
What separates ionizing from non-ionizing radiation?
The dividing line is energy per unit, not total intensity. Ionizing radiation carries enough energy in each individual photon or particle to knock an electron loose from an atom it strikes. That leaves a charged fragment behind, and inside a cell such fragments can break the chemical bonds holding DNA together. Non-ionizing radiation lacks that energy however strong the source. A powerful radio transmitter delivers far more total energy than a faint x-ray beam, yet it cannot ionize anything, because each individual wave falls below the threshold. Its effects are limited to heating and, at certain wavelengths, to chemical reactions in skin and eye.
| Form | Ionizing? | Familiar sources |
|---|---|---|
| Radio waves and microwaves | No | Broadcasting, mobile signals, microwave ovens |
| Infrared and visible light | No | Heat lamps, ordinary lighting |
| Ultraviolet | Mostly not, but it damages DNA by a separate chemical route | Sunlight, tanning devices |
| X-rays and gamma rays | Yes | Radiographs, CT scans, some cancer treatment |
| Alpha and beta particles | Yes | Radioactive decay, including radon indoors |
Where does everyday exposure come from?
Most exposure across a lifetime is natural background. Cosmic rays reach the ground after passing through the atmosphere, so exposure rises with altitude and during air travel. Rock and soil contain radioactive elements whose decay releases radon, a gas that can collect in enclosed indoor spaces and is the largest single natural contributor for many people. The body itself holds naturally radioactive potassium. Medical imaging is the largest manufactured contribution, and the amount varies enormously between a single dental film and a detailed cross-sectional study.
How is it used in medicine?
Two uses run in opposite directions. Imaging passes a small, measured quantity of ionizing radiation through the body and records what emerges, so the dose is held as low as a usable picture allows. Radiation therapy does the reverse, delivering a large dose deliberately into a defined volume of tissue in order to break the DNA of the cells there, relying on the fact that rapidly dividing cells repair such damage poorly. Both uses are planned and measured rather than incidental, and both are described in units of absorbed dose so the quantity involved can be compared and recorded.
Used in a sentence
The radiology report noted the estimated radiation exposure associated with the imaging study.
Good to know
Ionizing radiation, which includes medical x-rays, carries enough energy to damage DNA within cells, a property that distinguishes it from non-ionizing radiation such as radio waves, which does not have this effect.
Word origin
Where “radiation” comes from
From Latin radius, meaning ray or spoke, by way of radiare, meaning to emit rays.