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.
Although the passage of radiation through the body can cause damage, radiation can also be used to treat certain diseases, including cancer, often by directing beams of radiation at the tumor to destroy it. It is important to be able to quantify the amount, or dose, of radiation (known as dosimetry).
Taking into account all of the variables with radiation (amount, measured units, etc.) there needs to be a more meaningful units for the comparison of biological damage.
The Relative Biological Effectiveness (RBE) or Quality Factor (QF) of a type of radiation is defined as the number of rads of x-ray or gamma radiation that produces the same biological damage as 1 rad of the given radiation.
Individuals who work at nuclear plants, hospitals, and research are exposed to more than the general public. For that reason, the level of exposure is increased to 5 rem/yr whole body dose.
To protect themselves and to keep track of how much radiation they are exposed to, these individuals wear a dosimeter, typically a radiation film badge, which is a piece of film wrapped in light-tight material. Ionizing radiation passes through this material and darkens the film. The more exposure to radiation, the more exposed the film is.