What method is commonly employed to detect internal contamination?

The method commonly employed to detect internal contamination is the use of bioassays or a whole-body counter. Bioassays involve analyzing samples, such as urine or blood, to measure the amount of radioactive material present in the body. This method provides valuable information about the type and quantity of isotopes that may have been ingested or inhaled.

A whole-body counter is a specialized device designed to measure the radiation emitted from radioactive materials within the entire body. It allows for a non-invasive assessment and provides a direct measurement of internal contamination, making it particularly effective for monitoring radiation exposure in workers who may have been exposed to radioactive substances.

The alternative methods listed, such as visual inspection, magnetic resonance imaging (MRI), or ultrasound scanning, are not suitable for detecting internal contamination from radioactive materials. Visual inspection cannot identify internal radiological hazards, while MRI and ultrasound are imaging techniques used primarily for visualizing soft tissues and structures within the body rather than measuring radiation levels or detecting specific radioactive contaminants. Thus, bioassays and whole-body counters are the appropriate and commonly used methods for this purpose.