A Geiger counter (or Geiger–Müller counter) is an instrument used to detect and measure ionizing radiation (such as alpha particles, beta particles, and gamma rays).
How it works:
- Tube filled with gas
- At the heart of the counter is a Geiger–Müller tube filled with an inert gas (like helium, neon, or argon) at low pressure.
- Radiation enters the tube
- When radiation passes through, it ionizes the gas (knocks electrons off atoms).
- Electrical pulse created
- The released electrons cause a short burst of current.
- Each burst is counted as a “click” or displayed as a reading.
- Readout
- Results are shown as counts per second (CPS) or counts per minute (CPM), and sometimes converted into units of dose rate (like microsieverts per hour).
What it detects:
- Alpha particles: Detectable only if they enter the tube (can be blocked by paper or skin).
- Beta particles: Easily detected.
- Gamma rays & X-rays: Detected, but less efficiently (they’re very penetrating).
Everyday use:
- Radiation safety monitoring in labs and nuclear plants
- Checking contamination of surfaces or materials
- Used by health physicists, geologists, and sometimes hobbyists
- Fun fact: The clicking sound is iconic in movies, but in real devices, you often hear rapid clicks in high-radiation areas.