Geiger-Muller Tube
Definition
A gas-filled cylindrical tube with a thin entrance window and a high-voltage central wire. An ionising particle entering the tube triggers a Townsend avalanche that produces a measurable pulse. Cheap, robust, alpha/beta/gamma sensitive, and famously not energy-resolving; every pulse looks like every other pulse.
- Construction
- Gas-filled tube with thin entrance window, high-voltage central wire
- Mechanism
- Townsend avalanche produces a measurable pulse per ionising event
- Sensitivity
- Alpha, beta, and gamma sensitive
- Limitation
- Not energy-resolving; every pulse looks alike
Common questions
Why does the lack of energy resolution matter in forensic radiological work?+
A Geiger-Muller counter tells you that radiation is present and roughly how much, but not what isotope produced it, so identifying a specific radioactive source or distinguishing a medical isotope from a weapons-relevant one requires a spectroscopic detector such as a scintillator or semiconductor detector instead.
What is a Geiger-Muller tube best used for at a scene?+
Fast, rugged survey work such as screening a scene or person for the presence of elevated radiation before committing to slower, more sensitive spectroscopic instruments that identify the specific isotopes present.
Why is the thin entrance window on the tube significant?+
Alpha particles have very limited penetrating power and are stopped by ordinary materials, so a thin window is necessary to let them reach the gas fill at all; without it the tube would only register beta and gamma radiation.
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