We always are exposed to minute amounts of radiation. Cosmic rays that constantly bombard the earth contain radioactive rays. Some minerals that contain radiation have occurred naturally in the earth from the beginning. But exposure to large amounts of radiation is a relatively new danger as people are exposed to x-rays or to unintentional contamination from nuclear power plants, from radioactive transport vehicle crashes and construction incidents. Radiation is a general term that describes energy transmission.
Radiation takes several different forms, including sound, light and heat.
These forms can burn the eyes, sound can harm the ears and heat can burn. However, ionizing radiation is the most harmful and cannot be detected without special equipment. Ionizing radiation has the unique property of being able to disrupt atoms and, therefore, to damage the cells of the body. They do little damage if exposure is only external. They can be shielded off by material as weak as clothing or a sheet of paper.