Ionizing versus Nonionizing

Because health physics supports the uses of ionizing radiation it is helpful to discuss the reasons why this type of radiation is important. Not all radiation interacts with matter in the same way. Radiation that has enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to remove electrons, is referred to as “non-ionizing radiation.” Examples of this kind of radiation are sound waves, visible light, and microwaves.

Radiation that falls within the “ionizing radiation” range has enough energy to remove tightly bound electrons from atoms, thus creating ions. This is the type of radiation that people usually think of as “radiation.” These properties are taken advantage of in diagnostic imaging and to kill cancer cells.

Examples of ionizing radiation uses are fluoroscopes, CT scanners and nuclear medicine bone scans. Examples of non-ionizing radiation exposures in the clinical setting include Magnetic resonance imaging (MRI), ultrasound and LASERS.

A wavelength graph is shown below.

Background Radiation

People are constantly exposed to small amounts of ionizing radiation from the environment as they carry out their normal daily activities; this is known as background radiation. We are also exposed through some medical treatments and through activities involving radioactive material.

Annual background radiation is often used as a “baseline” exposure to compare occupational exposures (or even diagnostic imaging exposures such as chest x-rays) to what we are naturally exposed to in our everyday environment.

Background radiation consists of the radiation exposures received from both natural and man-made sources. The unit of exposure or “dose” is often in mrems or mSvs (for more info see Stanford’s Radiation Safety Manual). For someone residing in the US, the annual background exposure is approximately 6.3 mSv (633 mrem), but some locations can be much higher.

The highest known level of background radiation in the world affecting a substantial population is in Kerala and the Madras States in India where some 140,000 people receive an annual exposure which averages over 30 mSv (3000 mrem) per year from both gamma and radon radiation (478% more than what is average in the US).