Which type of detector is primarily used for detecting physical contamination on surfaces?

The primary purpose of a frisker is to detect physical contamination on surfaces, making it the correct choice in this context. Friskers are portable radiation detection instruments specifically designed to measure the presence of radioactive contamination on surfaces, such as floors, equipment, or personnel. They usually employ a probe or a sensitive detector that can easily be swept over areas of concern, providing immediate feedback on the contamination levels.

In contrast, a Geiger-Mueller counter is primarily used for measuring ionizing radiation in the air and can detect gamma and beta radiation, but it is not specifically tailored for identifying contamination on surfaces. Scintillator detectors are versatile for detecting various types of radiation and can provide good energy resolution, but they are also not specifically designed for surface contamination measurement. Lastly, liquid scintillators are generally utilized for detecting and measuring radioactivity in liquid samples rather than for surface contamination assessment. This specificity makes the frisker the most appropriate choice for detecting physical contamination on surfaces.