Portal monitors are instruments for external contamination measurement. They are used for monitoring personnel who exit a nuclear facility. Portal monitors are usually the last defense against contaminated people and equipment leaving the station. These detectors can simultaneously measure beta and gamma contamination. The total body surface, including hands, head, and feet, is measured by many beta gas flow proportional counters and several large additional gamma scintillation detectors positioned in the breast area (left and right side). Large scintillation detectors (plastic or liquid) are installed to be able to detect the passage of low levels of gamma activity. As they are only sensitive to gamma radiation, they can detect incorporated gamma activity if present. In this way, if some internal contamination exists, the worker is immediately sent for whole-body counting, and the dose assessment is much more accurate.