Hand & Shoe Monitors are instruments for surface contamination measurement. In nuclear facilities, Hand & Shoe Monitors are installed usually at the exit from the controlled areas, and workers are usually required to measure whether their hands and shoes are contaminated or not. 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. They are used in various locations in the station to detect beta-gamma contamination on hands, shoes, and clothing. These large area detectors have thin Mylar windows to detect beta radiation to allow low-energy beta particles to enter the detector. For example, they can easily detect the low-energy beta particles emitted by carbon-14 (Emax = 156 keV). 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.
