RAS question
A Geiger-Müller counter is used to detect:
Correct answer: (B) Ionizing radiation.
A Geiger-Mueller counter is used to detect and measure ionizing radiation.
Explanation
A Geiger-Mueller counter is a radiation detection and measuring instrument, so the answer is ionizing radiation. It detects alpha, beta and gamma radiation, and the NRC glossary explains the working principle: the instrument has a gas-filled tube with electrodes and an applied voltage. When ionizing radiation passes through the tube, it produces a short, intense pulse of current from the negative electrode to the positive electrode. The instrument measures or counts these pulses, and the number of pulses per second indicates the intensity of the radiation field. That is why the device is associated with radiation monitoring rather than ordinary mechanical waves, magnetic effects or ground vibrations.
Why the other options are wrong
- (A) Sound waves are detected by microphones, whereas a Geiger-Mueller counter responds to ionization events inside its gas-filled tube.
- (C) Magnetic fields are detected by magnetometers; the Geiger-Mueller counter described here measures pulses produced by ionizing radiation, not magnetic-field strength.
- (D) Earthquakes are detected by seismographs, while a Geiger-Mueller counter is a portable radiation instrument for counting radiation-induced pulses.
Concept
This tests basic scientific instruments and their applications, a recurring RAS Science and Technology area because many questions ask candidates to match a device with the physical quantity it detects. The key distinction is that the Geiger-Mueller counter belongs to radiation detection, not sound, magnetism or seismic measurement.