Which of the following instruments is used in detecting the presence of radiation?

Step 1: Analyze the question The question asks which instrument detects radiation, such as alpha, beta and gamma radiation from radioactive substances.

Step 2: Explain the concept Radioactive substances emit ionizing radiation. To detect it, we need a device that responds to the ionization this radiation causes. The Geiger-Muller counter does exactly this.

How a Geiger-Muller counter works:

• It has a tube filled with a low-pressure gas (e.g., argon).
• When radiation enters the tube, it ionizes the gas.
• The ions produce a brief electrical pulse.
• The pulse is counted and shown as clicks or a reading on a meter.

Step 3: Check each option

• A. Cathode ray tube: It produces a beam of electrons (used in old TVs and in studying electrons). It does not detect radiation.
• B. Geiger-Muller counter: It detects and measures ionizing radiation. ✔
• C. Mass spectrometer: It measures the masses of isotopes and the relative abundance of ions. It is not a radiation detector.
• D. X-ray tube: It produces X-rays rather than detecting them.

Step 4: Answer The correct option is B. Geiger-Muller counter.

Exam tip: Remember "Geiger = Gauge of radiation". Detectors include the Geiger-Muller counter, scintillation counter and photographic film badges. Tubes (cathode ray, X-ray) produce beams, while a spectrometer analyzes masses.