Which device is used to detect and measure ionizing radiation?

The Geiger-Müller counter is a widely used device specifically designed for the detection and measurement of ionizing radiation. It operates by sensing the ionization produced in a gas contained within a tube when it is exposed to radiation. When ionizing radiation passes through the gas, it causes ionization events, resulting in electrical pulses that can be measured and counted. This device provides real-time readings, making it essential in various applications such as safety monitoring in nuclear facilities, environmental radiation assessments, and personal dosimetry for workers in radiation-related fields.

In contrast, the other devices listed are used for different purposes: a thermometer measures temperature, a calorimeter measures heat to determine thermal properties, and a barometer measures atmospheric pressure. None of these instruments are suitable for detecting or measuring ionizing radiation, which is why they are not the correct choice in this context.