What type of instrument is commonly used to detect and measure radioactivity?

The Geiger-Muller counter is a vital instrument for detecting and measuring radioactivity because it is specifically designed to sense ionizing radiation, such as alpha particles, beta particles, and gamma rays. This device operates by using a Geiger-Muller tube filled with gas that becomes ionized in the presence of radiation. When radiation passes through the tube, it creates ion pairs, leading to a cascade of electrons that produces a detectable electrical pulse. The Geiger-Muller counter is renowned for its efficiency and portability, making it an essential tool in various fields, including nuclear safety, medical applications, and environmental monitoring.

In contrast, the other instruments mentioned serve different purposes unrelated to radioactivity measurement. A thermometer measures temperature, a dosimeter specifically records the dose of radiation exposure over time rather than detecting it instantaneously, and a barometer measures atmospheric pressure. Together, these roles highlight the specialized function of the Geiger-Muller counter in the context of radiation detection and measurement.