Full-Body Monitors, or Whole-Body Monitors, are instruments for surface contamination measurement. They are used for personnel exit monitoring, the term used in radiation protection for checking for external contamination (or surface contamination) of a whole body of a person leaving radioactive contamination controlled area. The main purpose is to prevent the spread of contamination outside the controlled area. Generally, surface contamination means that radioactive material has been deposited on surfaces. It may be loosely deposited, much like ordinary dust, or a chemical reaction may firmly fix it. This distinction is important, and we classify surface contamination based on how easily it can be removed.
These monitors may utilize gas-flow proportional counters with a large area, and workers must use them every time they leave the controlled area. These monitors usually require a two-step measurement. First, the measured person faces the detectors. When they’ve done their thing, the person turns around to monitor his/her back. Proximity sensors check that the person is standing in the right position for the measurement. If not, the monitor talks to the person and tells them what to do. Full-body monitors can detect beta and gamma contamination in the body. These large area detectors have thin Mylar windows to detect beta radiation to allow low-energy beta particles to enter the detector. The voltage must be kept constant when instruments are operated in the proportional region. If a voltage remains constant, the gas amplification factor also does not change. Proportional counter detection instruments are very sensitive to low levels of radiation. The proportional counter can detect alpha, beta, and gamma radiation by proper functional arrangements, modifications, and biasing. The electronics sort the alpha and the beta-gamma pulses. This feature may be used in alpha, beta-gamma Hand & Shoe Monitors, Full-Body Monitors, and some alpha Contamination Monitors. Although such detectors are very sensitive, their drawback is that the windows are punctured quite easily by misuse. The detector is then dead until its window is repaired.