Class 12 > Unit # 28: Particle Physics > Geiger Muller Counter

Talha's Physics Academy

Construction and Working of Geiger-Muller Counter

Geiger-Muller Counter

A Geiger-Muller counter (GM counter) is a type of gas radiation detector used to measure ionizing radiation. It is a portable and versatile device commonly employed for detecting the presence and intensity of various types of ionizing radiation, including alpha particles, beta particles, and gamma rays.

Construction

The GM counter consists of a hollow metallic chamber as shown in the figure that acts as a cathode. A thin wire anode is also placed along its axis. The chamber has a sealed window, through which the radiation enters the chamber. The chamber is filled with an inert gas at low pressure. There is a counter connected to this system to measure the radiation.

Figure: Construction of a Geiger-Muller counter showing the metallic cathode chamber, wire anode, sealed window, and gas filling.

Working

The chamber is filled with an inert gas (helium, neon, or argon) at low pressure. A high voltage is applied to this chamber. The metallic chamber will conduct electricity. When radiation enters the chamber through the window, the photons in the radiation will ionize the inert gas inside the chamber. This will make the gas conductive. The electrons produced due to ionization are accelerated due to the potential that we applied and these electrons cause even more ionization. The ionized electrons travel towards the anode. The anode is connected to a counter. The counter counts the electrons reaching the anode. This is how we measure radiation.

Resultant Curve: Geiger Plateau

The performance of a GM counter is typically illustrated by the Geiger Plateau curve, which shows the count rate versus the applied voltage.

Figure: Geiger Plateau curve showing count rate versus applied voltage with initial, threshold, plateau, and continuous discharge regions.

1. Initial Region: At low voltages, no significant ionization occurs, so the count rate is very low.
2. Threshold Region: As voltage increases, the counter starts to detect ionizing events. The count rate begins to rise sharply.
3. Geiger Plateau: At a certain voltage range, the count rate levels off and remains relatively constant. This is the operational region of the GM counter. The plateau indicates that each ionizing event is creating a detectable pulse, and the counter is functioning reliably.
4. Continuous Discharge Region: If the voltage is increased too much, continuous discharge occurs, where the counter no longer operates correctly, and the count rate rises rapidly.

© 2026 Talha's Physics Academy. All rights reserved.