Full-Body Monitors, or Whole-Body Monitors, are instruments for surface contamination measurement. They are used for personnel exit monitoring, which is the term used in radiation protection for checking for external contamination (or surface contamination) of a whole body of a person leaving a 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 it may be quite firmly fixed by chemical reaction. This distinction is important, and we classify surface contamination on the basis of how easily it can be removed.
These monitors may utilize gas-flow proportional counters with a large area, and workers must use it every time they leave the controlled area. These monitors usually require a two-step measurement. First the measured person face the detectors. When they’ve done their thing, the person turn 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 actually talks to the person and tells what to do. Full-body monitors are able to detect beta and gamma contamination on the body. In order to detect beta radiation, these large area detectors have thin Mylar windows to allow low-energy beta particles to enter the detector. When instruments are operated in the proportional region, the voltage must be kept constant. 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. By proper functional arrangements, modifications, and biasing, the proportional counter can be used to detect alpha, beta, gamma radiation. The electronics sorts the alpha, the beta-gamma pulses. This feature may be used in alpha, beta-gamma Hand & Shoe Monitors, Full-Body Monitors, 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.
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