Posted on February 14, 2019
About Radiation Detectors - Advantages & Disadvantages
Each type of radiation detectors has its advantages and disadvantages. A wide range of detectors exist for measuring and quantifying ionizing radiation. The selection of a radiation detector is guided by measurement requirements. Some detectors can quantify radiation energy, where others only count ionizing events. The design and shielding of a radiation detector also affect its sensitivity to different ionizing sources, including alpha, beta, and gamma radiation.
Those incorporating GM tubes, are more commonly used due to ease of handling, low cost, and accuracy, and reliable. For applications where high efficiency for gamma radiation is needed, scintillation devices are best. Scintillation detectors are commonly used in medical applications such as digital radiography, fluoroscopy or CT scans. Most scintillation detectors will not detect alpha or beta radiation.
Geiger tubes are rugged and relatively inexpensive to manufacture. The design of a GM detector strongly affects its sensitivity to alpha, beta, and gamma radiation sources each having different penetrating characteristics. Geiger-Müller detectors for alpha and beta radiation commonly use tube geometries with an ultrathin window to increase the likelihood that less penetrating radiation will reach the inside of the detector. The detection of gamma radiation results primarily from the interaction of gamma rays with the sidewall of the detector. The chamber geometry, gas, wall material, and thickness are all design factors in the sensitivity limits of GM detectors.
Scintillation detectors are used when quantification of ionizing energy is of interest. They utilize the interaction of ionizing radiation to produce UV and/or visible light. A calibration transfer function allows the intensity of captured light to be related to the energy of the incident radiation. The majority of light conversion in scintillation materials occurs via fluorescence. Fluorescence allows for fast detector response times and quantification of moderate- to high-level radiation. Scintillation materials are chosen based on the type of radiation to be measured.
Solid-state detectors based on semiconductor diodes are used when improved energy resolution and radionuclide identification capabilities are required. These detectors rely on the production of electron-hole pairs within a diode depletion region resulting from incident ionizing radiation. In a solid-state device under a reverse bias, these charge carriers can be directly swept to electrodes producing a current signal before recombining. Solid-state detectors can offer greater energy resolution than scintillation detectors.
There are several limitations associated with the use of solid-state detectors. To increase the diode depletion region which forms the interaction volume of the detector, production of high-purity semiconductor materials, like silicon or germanium, is required. Leakage current in the diode due to room-temperature excitation of charge carriers can significantly degrade the noise performance of solid- state detectors. Cooling to cryogenic temperatures is generally required for optimal resolution and operation. Solid-state detectors and spectrometers are typically more expensive than alternative technologies.
Additional classes of detectors exist. Each detector type possesses unique advantages and disadvantages depending on survey requirements. Understanding of the differences between detector designs and capabilities can help facilitate interpretation and discussion of radiation measurements.
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