Correct Answer:
B. Geiger counter
Radioactivity involves the spontaneous emission of particles or energy from unstable atomic nuclei. Detecting this invisible radiation requires specialized instruments. The correct answer is Geiger counter.
A Geiger counter, or Geiger-Müller counter, is a primary instrument used to detect ionizing radiation such as alpha particles, beta particles, and gamma rays. It works by using a gas-filled tube; when radiation enters, it ionizes the gas, creating a brief electrical pulse that is amplified and registered as a click or a digital reading. This allows for the measurement of radiation levels.
- Polarimeter is incorrect because it measures the rotation of plane-polarized light by optically active substances, a property unrelated to radioactivity.
- Calorimeter is incorrect because it measures heat changes in chemical reactions or physical processes, not ionizing radiation.
- None of these is incorrect because the Geiger counter is a well-established and widely used device for detecting radioactivity.