While scientists think of these emissions in highly mathematical terms, they can be visualized either as subatomic particles or as rays. Radiation's effects on humans can best be understood by first examining the effect of radiation on atoms , the basic building blocks of matter. Normally, the number of protons in the center of the atom equals the number of electrons in orbit. An ion is any atom or molecule that does not have the normal number of electrons. Ionizing radiation is any form of radiation that has enough energy to knock electrons out of atoms or molecules, creating ions.
Measurement lies at the heart of modern science, but a number by itself conveys no information.
The units chosen will vary with the purpose of the measurement. For example, a cook will measure butter in terms of tablespoons to ensure the meal tastes good, while a nutritionist may be more concerned with measuring calories, to determine the effect on the diner's health. The variety of units used to measure radiation and radioactivity at times confuses even scientists, if they do not use them every day. It may be helpful to keep in mind the purpose of various units. What creates the complexity is that our instruments measure physical effects, while what is of interest to some are biological effects.