What is the radiation-sensitive portion of a scintillation detector primarily composed of?

The radiation-sensitive portion of a scintillation detector is primarily composed of a light-emissive crystal. This crystal plays a vital role in the detection of radiation by absorbing energy from incoming radiation events, such as gamma rays or alpha particles, and subsequently re-emitting that energy as visible light. This emitted light can then be detected by photomultiplier tubes or photodiodes, converting the light signal into an electrical pulse that can be measured and analyzed.

The choice of light-emissive crystal is important because different materials have varied efficiencies in converting radiation energy into light, as well as different spectral outputs, which can affect the overall performance and sensitivity of the detector. Some common materials used as scintillation crystals include sodium iodide (NaI) doped with thallium, and cesium iodide (CsI).

In contrast, the other materials listed—plastic, metal, and gas—are not primarily responsible for the scintillation process in detectors. While some plastic scintillators can be effective in certain applications, they do not have the same light-emitting efficiency as high-atomic-number crystals. Metals typically serve as structural components or shielding rather than active sensing materials. Gases, like those found in gas-filled detectors, operate on different