Which material is commonly used in scintillation detectors for gamma radiation measurement?

• A. NaI(Tl)
• B. Plastic scintillator
• C. Gadolinium oxide
• D. CsI(Tl)

Answer: (A)

For gamma detection, you want a scintillator that maximizes the chance a gamma interacts and then converts that energy into visible light that a photodetector can read. A material with high density and high atomic number does that job well, and sodium iodide doped with thallium fits the bill. The iodine provides a high effective Z, and the crystal’s density means gamma rays are more likely to interact inside it. The thallium dopant produces bright scintillation light with a fast decay time and emission in a range that photomultipliers commonly detect, giving good signal yield and clear energy information. Sodium iodide crystals are also easy to grow into large, transparent pieces, relatively inexpensive, and they offer good energy resolution for gamma rays. These factors together make NaI(Tl) the go-to scintillator for gamma spectroscopy.

Plastic scintillators, while fast, have much lower gamma interaction probability due to their low Z and density, so they’re less efficient for gamma measurements. Gadolinium oxide isn’t a standard scintillator material for gamma spectroscopy, and CsI(Tl) is also used in detectors, but NaI(Tl) has been the traditional, widely adopted choice because of its balanced performance and practicality.