A dosimeter is an instrument used to measure exposure to ionizing radiation, such as alpha or beta particles, neutrons, gamma rays, or X-rays. It is an essential tool for people working in situations where they are exposed to radiation. A dosimeter is a device that measures the dose absorption of external ionizing radiation and is used by the person being monitored when using it as a personal dosimeter. It is also a record of the radiation dose received. Modern electronic personal dosimeters can provide a continuous reading of the cumulative dose and the current dose rate, and can warn the user with an audible alarm when a specified dose rate or cumulative dose is exceeded.
Other dosimeters, such as thermoluminescent or film types, require post-use processing to reveal the cumulative dose received, and cannot give a current dose indication while in use. Badges are not designed to protect people from radiation. The purpose of a dosimetry badge is to document occupational radiation exposure and demonstrate compliance with annual dose limits and ALARA levels (As Low As Reasonably Achievable). Badges also provide valuable information to the Radiation Safety Office regarding the safety of the work environment and the quality of the radiation safety program established for the area.