Geiger Counter (Geiger-Müller Tube)

A Geiger counter is a widely used instrument for detecting and measuring ionizing radiation. It utilizes a Geiger-Müller (GM) tube as the detection probe. Known for their robustness and cost-effectiveness, GM counters are a standard choice for radiation monitoring in industrial, safety, and research applications.

Operating Principle and the Role of High Voltage

A GM tube consists of a cylinder filled with inert gas. To operate, a stable high-voltage must be applied between the anode and cathode. When radiation enters the tube, it ionizes the gas, and the high electric field accelerates the resulting electrons, causing an avalanche effect. This generates a detectable current pulse. Because the detection relies on maintaining a specific electric field, a stable high-voltage power supply is critical for accurate and reliable measurement.

Measurement and Output

The instrument counts these current pulses to display a count rate (counts per second, cps) or a dose equivalent rate (Sv/h) calibrated against a standard source, typically Cesium-137. GM tubes can detect beta particles, gamma rays, and X-rays. For precise dose measurements of X-rays or nuclides with varying energy levels, energy-compensated GM tubes are often used to correct for sensitivity differences.

Comparison with Other Detectors

While "Geiger counter" is often used as a generic term, other radiation detectors include scintillation detectors, semiconductor detectors, and ionization chambers. GM counters are ideal for general-purpose detection but may have lower detection efficiency for high-energy gamma rays compared to scintillators. They are also subject to "dead time" effects, which can limit accuracy at very high dose rates.