Radiation Dosimetry is the science of measuring radiation dosage. This is typically accomplished by a device known as an ion chamber. The chamber is filled with noble gases such as neon and argon. When placed under a beam of radiation, the chamber produces a very small electrical current. This current is measured by a very sensitive device called an electrometer. There is a direct relation between the amount of charge produced and the radiation dosage. This ratio is different for every ion chamber, and must be verified experimentally every few months. This process is known as dose calibration.
Common units of radiation dosage are rads (RAD), grays (Gy), or roentgens. Radiation beams are used in the field of radiation oncology to destroy cancerous tumors because radiation is very destructive to living tissue. Ironically, radiation also causes cancer! For this reason, radiation oncologists must be absolutely certain that their beams are the correct shape and intensity. Otherwise, they might do more harm to their patients than good.