Answer:
The instrument that is commonly used to measure radio activity is the Geiger counter.
Explanation:
The Geiger counter is used to measure certain ionizing radiations (alpha, beta particles or gamma radiation and x-rays, but not neutrons). This instrument of measurement, whose principle was imagined circa 1913 by Hans Geiger, was perfected by Geiger and Walther Müller in 1928.
When ionizing radiation enters the meter, it ionizes the gas, that is, it causes the electrons to be released. These electrons multiply rapidly by electronic avalanche, making the gas conducting for a short time (phenomenon of electric discharge). After amplification, the electrical signal thus produced is recorded and translated into a visual indication (needle, lamp) or sound (click).
