Britannica
Sources used in this answer
How does a scintillation counter detect gamma rays?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
luminescence
Figure 1: Energy levels of a luminescent centre (see text).
A scintillation counter detects gamma rays by utilizing a material known as a scintillator, which produces a flash of light when struck by ionizing radiation. The process follows these general steps:12
- Interaction: When a gamma ray enters the scintillator, it interacts with the material, creating excited atomic or molecular states. As these states decay, they emit visible or ultraviolet light photons.3
- Light Collection: The scintillator is typically coated with an optically reflective material to ensure that the emitted light is directed toward an exit window.3
- Conversion: The light flashes are directed into a light sensor, such as a photomultiplier tube or a photodiode, which is in optical contact with the exit window.32
- Amplification and Counting: The sensor converts the light photons into electrical pulses. In a photomultiplier tube, these pulses are amplified significantly—often by a factor of a million—allowing the device to count the individual events and measure the energy of the incident gamma rays.12
Materials like thallium-activated sodium iodide [NaI(Tl)] are frequently used for this purpose because their high atomic number makes them highly effective at stopping and detecting gamma rays.14