Gamma counters measure gamma radiation in samples using luminescent crystals that emit light when photons from gamma rays interact with them. Gamma radiation is harmful and can damage or kill cells. The accuracy of the counter depends on the crystal used, and modern gamma counters can have multiple detectors and sample channels. Proper calibration is important, and some older meters may need to be calibrated by hand. Gamma counters are typically used in research laboratories and are not easily transportable due to their lead shielding.
The device known as a gamma counter measures the gamma radiation in a sample. Working on the same principle as a scintillation detector, these counters use crystals that emit light when photons from gamma rays interact with them. Samples are usually placed in test tubes, which are then fed into the machine. Gamma counters are typically used in research laboratories as most are not portable.
Gamma radiation, or gamma rays, is a harmful type of high-energy radiation that consists of photons of light or quantum particles. Photons are emitted when radioactive substances decay or try to become stable. Unlike less harmful types of radiation, gamma rays are not blocked by skin or clothing and can enter the body, damaging or killing cells. Lead is generally used to protect people from the harmful effects of gamma radiation.
Like a scintillation detector, gamma counters rely on crystals with luminescent properties to function. This means that these crystals light up, or sparkle, when they come into contact with gamma radiation. The more they light up, the more radiation a sample emits. Light energy is usually converted into electrical energy via a photomultiplier to provide scientists with a meaningful measurement.
The accuracy of the counter depends on the crystal used. If the radiation is low, and therefore interacts little with the luminescent crystal, the photons of light may not register. Conversely, if the radiation is extremely high, it may be powerful enough to pass directly through the crystal without interacting enough to also produce light. Thick crystals help reduce these non-reactions, and therefore are extremely important in quality gamma counters.
Modern gamma counters can have multiple detectors and sample channels. The machines usually also have lead shielding to help protect the researchers from radiation. Many gamma counters are roughly the size of cash registers or copiers, with a small electronic screen attached for readings.
There are also small gamma meters, not much larger than a square foot (0.3m2). However, even small meters are not easily transportable, as the lead shielding makes them extremely heavy despite their size. A meter the size of one square foot can weigh up to 55 pounds (25 kg).
Proper calibration is extremely important when working with gamma counters because they produce such precise measurements. Many meters have internal calibration which is based on light emitting diodes. However, some older meters may need to be calibrated by hand. During manual calibration, a substance with a known radiation and approximately the same volume as the sample to be tested is used as a reference.
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