Final answer:
The instrument used to check a person's exposure to radiation is the Geiger counter.
Step-by-step explanation:
The instrument that is used routinely to check a person's exposure to radiation is the Geiger counter. It is a portable device that detects and measures ionizing radiation by using a gas-filled tube. When radiation particles pass through the tube, it creates an electric current, which is then amplified and counted by the Geiger counter.
Learn more about Radiation exposure measurement