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Why do professionals prefer scintillation instruments? Despite common myths, high-end detectors used by special services and customs are not sensitive to alpha and beta radiation. This article explores the reasons behind this preference, highlighting the superior sensitivity of scintillation devices to gamma radiation and their efficiency in real-world applications.
A common myth is that to detect radiation effectively, a detector must be sensitive to both alpha and beta radiation. However, professional equipment costing tens of thousands of dollars, used by special services or customs officers, is often not sensitive to alpha and beta radiation. So why do professionals ignore alpha and beta radiation? There are several reasons for this:
This is especially evident when compared to Geiger Counters, which detect radiation through the interaction of light gas in the Geiger tube. Due to the low density of the gas, much of the radiation passes through without interaction and is not registered. In contrast, scintillation instruments use high-density crystals for detection. As gamma rays pass through the dense crystal, they interact and are registered much more efficiently. The device records 5-10 pulses every second even in natural background conditions. With such a volume of data, the device can easily detect any changes in the radiation background.
Detectors register particles too infrequently, so Geiger counter devices cannot quickly show small changes in the radiation background. For example, the most popular Geiger counter, the SBM-20, takes 40 seconds to detect a statistical difference between 0.08 µSv/h and 0.20 µSv/h. A scintillation sensor like the Radiacode can register a similar change in less than 1 second. For special services or customs, such a long measurement time is unacceptable.
Scintillation detectors have a special characteristic: the lower the energy of gamma radiation, the better they detect it. On an X-ray of bones, we see how weak gamma radiation does not pass through dense bones. The scintillation crystal, which is the basis of the scintillator, is also very dense. The lower the energy of gamma radiation, the more the detector interacts with radiation, and the higher the detection efficiency. Simply put, the dense crystal does not allow radiation to pass through, and registers all of it.
All beta and alpha radiation sources emit weak gamma (X-ray) radiation. Alpha decay almost always leads to the instability of the atomic nucleus, which results in weak gamma radiation. This radiation often has very low energy, which scintillation detectors register best. Beta decay is characterized by bremsstrahlung gamma radiation, which appears when a beta particle hits the atoms of a substance. The efficiency of this process is not very high, but due to the incredible sensitivity of scintillators to weak gamma radiation, it is sufficient for detection. Also, beta and alpha emitters often have their X-ray and gamma lines and decay products.
High sensitivity to low-energy gamma radiation in scintillation instruments can lead to incorrect dose rate readings, so compensation for this effect should be applied in such devices. Radiacode has this compensation. This is why two independent values and graphs are displayed. The first is the registered pulses per second by the detector. The second is the energy-compensated dose rate, where the device makes corrections. By displaying two independent values, the device benefits in both sensitivity and accuracy.
This results in a paradoxical situation: scintillation instruments often have a higher response to beta and alpha radiation sources than devices capable of registering beta and alpha radiation. Additionally, it’s important to note that alpha and beta radiation are easily shielded. Placing the source in a plastic box is enough for alpha and beta radiation to disappear. However, weak gamma radiation easily passes through the box, and the scintillation detector registers it.
