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    Scintillation Detector

    Scintillation Detector

    Scintillation detectors consist of a solid material that will emit light when exposed to radiation.

    From: Environmental Forensics, 1964

    Related terms:

    ScintillatorAmplifierTransistorNeutronsGamma RayPhotomultiplierPhotonsElectric PotentialScintillation

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    X-ray Fluorescence Spectrometers

    Utz Kramar, in Encyclopedia of Spectroscopy and Spectrometry, 1999

    Scintillation detectors

    Scintillation detectors are used for the determination of the high-energy part of the X-ray spectrum. In scintillation detectors the material of the detector is excited to luminescence (emission of visible or near-visible light photons) by the absorbed photons or particles. The number of photons produced is proportional to the energy of the absorbed primary photon. The light pulses are collected by a photo- cathode. Electrons, emitted from the photocathode, are accelerated by the applied high voltage and amplified at the dynodes of the attached photomultiplier (Figure 3). At the detector output an electric pulse proportional to the absorbed energy is produced. The average energy necessary to produce one electron at the photocathode is approximately 300 eV. For X-ray detectors, in most cases NaI or CsI crystals activated with thallium are used. These crystals offer a good transparency, high photon efficiency and can be produced in large sizes.

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    Detection Systems and Instrumentation

    PETER B. VOSE, in Introduction to Nuclear Techniques in Agronomy and Plant Biology, 1980

    Detector Systems for Scintillation Counting

    A scintillation detector consists of a crystal or other phosphor coupled with its mount to a PM tube with a silicone oil light-couple. The oil light-couple is necessary to obtain an intimate connection of the phosphor with the photomultiplier to ensure the efficient passage of very small light photons. The oil must have a refractive index similar to the glass of the tube. As of course it is light sensitive, the whole counter assembly is held in a light-tight metal counter-tube or support-tube, one end of which accommodates the multi-pin photomultiplier tube base.

    Such a detector may be mounted upright, i.e., scintillator uppermost, for “end-on” or “well” counting of gamma samples. Strong beta emitters may also be counted in a well-type counter. Alternatively the detector may be inverted for so-called “windowless” counting of beta emitters, in which the sample on a planchet is placed beneath the scintillator. Simple arrangements of this sort are shown in Fig. 4.1.

    In the case of liquid scintillation counting the vial containing the sample and scintillator is placed in direct optical contact with the end of the PM tube. In order to protect the PM tube from the light during sample changing, a light-tight automatic shutter device is always built-in to these instruments to prevent accidental exposure which would greatly increase the background count.

    Individual PM tubes of nominally identical manufacture differ in the degree of “noise” that they produce, due to normal manufacturing tolerance. It is therefore usual to select “low noise” tubes for the more demanding scintillation counting applications, such as liquid scintillation counting of 3H and 14C.

    A constant temperature is also important for stable photomultiplier performance, and in practice for the liquid scintillation counting of low activity beta samples this has meant refrigeration. Thus the detector may be put in an ordinary refrigerator, or cooling coils incorporated in the lead shielding, or refrigeration units built-in to the larger automatic equipment. With the older type of PM tube there is a substantial reduction in thermal or “dark” noise when the operating temperature is reduced from 15-80°C to 5°C, but little improvement is gained by working at still lower temperatures, and 0–5°C can be regarded as a practical working temperature range for these tubes.

    Nowadays, the more recently developed PM tubes such as the Beckman-RCA tube can be operated with high efficiency at ambient temperatures, and refrigeration is no longer necessary for this type of tube, exceptionally in very hot conditions where refrigeration may be used to keep the ambient temperature at about 15°C. A constant operating temperature still remains important however.

    By comparison, reduced operating temperatures have not usually been necessary for gamma counting with a scintillation crystal. This is because the gamma photons are of higher energy and the amount of light produced in a sodium iodide crystal is much greater than that produced by a weak beta emitter in a scintillation liquid. In the latter case the pulses produced in the PM only just exceed the thermal noise pulses of the PM, and thus every effort must be made to keep thermal noise to a minimum for liquid scintillation counting.

    Although a basic scaling assembly can certainly be used for the scintillation counting in integral mode of energetic gamma emitters, actual practice favours much more sophisticated arrangements. Thus both for solid and liquid scintillation counting, equipment with pulse height analysis facilities has become the general rule. By means of variable lower and upper discriminators it is possible to accept only pulses which pass through the “window” of the discriminator. Thus noise pulses with amplitudes less than or greater than the window are rejected.

    स्रोत : www.sciencedirect.com

    Scintillation counter

    Scintillation counter

    From Wikipedia, the free encyclopedia

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    Schematic showing incident high energy photon hitting a scintillating crystal, triggering the release of low-energy photons which are then converted into photoelectrons and multiplied in the photomultiplier

    A scintillation counter is an instrument for detecting and measuring ionizing radiation by using the excitation effect of incident radiation on a scintillating material, and detecting the resultant light pulses.

    It consists of a scintillator which generates photons in response to incident radiation, a sensitive photodetector (usually a photomultiplier tube (PMT), a charge-coupled device (CCD) camera, or a photodiode), which converts the light to an electrical signal and electronics to process this signal.

    Scintillation counters are widely used in radiation protection, assay of radioactive materials and physics research because they can be made inexpensively yet with good quantum efficiency, and can measure both the intensity and the energy of incident radiation.

    Contents

    1 History 2 Operation

    3 Detection materials

    4 Detector efficiencies

    4.1 Gamma 4.2 Neutron 5 Applications

    5.1 Selection guidance for handheld use

    6 Radiation protection

    6.1 Alpha and beta contamination

    6.2 Gamma 7 As a spectrometer 8 See also 9 References

    History[edit]

    The first electronic scintillation counter was invented in 1944 by Sir Samuel Curran[1][2] whilst he was working on the Manhattan Project at the University of California at Berkeley. There was a requirement to measure the radiation from small quantities of uranium and his innovation was to use one of the newly-available highly sensitive photomultiplier tubes made by the Radio Corporation of America to accurately count the flashes of light from a scintillator subjected to radiation. This built upon the work of earlier researchers such as Antoine Henri Becquerel, who discovered radioactivity whilst working on the phosphorescence of uranium salts in 1896. Previously scintillation events had to be laboriously detected by eye using a spinthariscope which was a simple microscope to observe light flashes in the scintillator. The first commercial liquid scintillation counter was made by Lyle E. Packard and sold to Argonne Cancer Research Hospital at the University of Chicago in 1953. The production model was designed especially for tritium and 14C which were used in metabolic studies in vivo and in vitro.[3] Shortly thereafter Packard Instrument Company began production of a Tri-Carb Liquid Scintillation Counter which incorporated an automatic sample changer. This advance greatly improved analysis in the field of molecular biology by allowing serial counts involving hundreds of samples unattended and overnight.

    Operation[edit]

    Apparatus with a scintillating crystal, photomultiplier, and data acquisition components.

    animation of radiation scintillation counter using a photomultiplier tube.

    When an ionizing particle passes into the scintillator material, atoms are excited along a track. For charged particles the track is the path of the particle itself. For gamma rays (uncharged), their energy is converted to an energetic electron via either the photoelectric effect, Compton scattering or pair production.

    The chemistry of atomic de-excitation in the scintillator produces a multitude of low-energy photons, typically near the blue end of the visible spectrum. The quantity is proportional to the energy deposited by the ionizing particle. These can be directed to the photocathode of a photomultiplier tube which emits at most one electron for each arriving photon due to the photoelectric effect. This group of primary electrons is electrostatically accelerated and focused by an electrical potential so that they strike the first dynode of the tube. The impact of a single electron on the dynode releases a number of secondary electrons which are in turn accelerated to strike the second dynode. Each subsequent dynode impact releases further electrons, and so there is a current amplifying effect at each dynode stage. Each stage is at a higher potential than the previous to provide the accelerating field.

    The resultant output signal at the anode is a measurable pulse for each group of photons from an original ionizing event in the scintillator that arrived at the photocathode and carries information about the energy of the original incident radiation. When it is fed to a charge amplifier which integrates the energy information, an output pulse is obtained which is proportional to the energy of the particle exciting the scintillator.

    The number of such pulses per unit time also gives information about the intensity of the radiation. In some applications individual pulses are not counted, but rather only the average current at the anode is used as a measure of radiation intensity.

    The scintillator must be shielded from all ambient light so that external photons do not swamp the ionization events caused by incident radiation. To achieve this a thin opaque foil, such as aluminized mylar, is often used, though it must have a low enough mass to minimize undue attenuation of the incident radiation being measured.

    स्रोत : en.wikipedia.org

    Scintillation Counter

    Scintillation Counter is an instrument that is used for measuring ionizing radiation. Explore its uses and applications with more related physics concepts at BYJU'S.

    PhysicsElectromagnetic WavesScintillation Counter

    Scintillation Counter

    Scintillation Counter What is Scintillation Counter?

    A scintillation Counter is an instrument that is used for measuring ionizing radiation. “It comprises the scintillator that generates photons in response to incident radiation”, a PMT tube is used to convert an electronics and electric signal to process the signal.

    A scintillation counter is used to detect gamma rays and the presence of a particle. It can also measure the radiation in the scintillating medium, the energy loss, or the energy gain. The medium can either be gaseous, liquid, or solid. The scintillator counter is generally comprised of transparent crystalline material such as glasses, liquids, or plastics. One sector of the scintillators is placed (optical contact) with the pin code.

    A charged particle loses energy when passing through the scintillator thus leaving the trail of excited molecules and atoms. A rapid interatomic transfer of electronic excitation energy follows, which leads to the burst of scintillator material luminescence characteristics. The scintillation response,  when a particle stops leading to the light output. The energy loss of a particle is measured when a particle passes completely through a scintillator.

    Applications of Scintillation Counter

    Scintillation Counters are widely used in radioactive contamination, radiation survey meters,  radiometric assay, nuclear plant safety, and medical imaging, which are used to measure radiation.

    There are several counters mounted on helicopters and some pickup trucks for rapid response in case of a security situation due to radioactive waste or dirty bombs.

    Scintillation counters are designed for weighbridge applications, freight terminals, scrap metal yards, border security, contamination monitoring of nuclear waste, and ports.

    It is widely used in screening technologies, In vivo and ELISA alternative technologies, cancer research, epigenetics, and Cellular research.

    It also has its applications in  protein interaction and detection, academic research, and pharmaceuticals.

    A liquid Scintillation Counter is a type of scintillation counter that is used for measuring the beta emission from the nuclides.

    Stay tuned with BYJU’S to learn more about interesting concepts like optics, thermodynamics, mechanics, and more with the help of interactive and engaging video lessons.

    Frequently Asked Questions

    What does scintillation efficiency mean?

    The ratio of the energy of scintillation light to the energy deposited is known as scintillation efficiency.

    What is the purpose of the scintillation counter?

    The scintillation counter is used for detecting and for measuring ionizing radiation.

    What is the use of a liquid scintillation counter?

    The liquid scintillation counter is used for detecting radioactivity. It is an analytical method used for measuring radioactivity when light photons are emitted by the sample.

    Give an example of a scintillation crystal.

    Sodium iodide doped with thallium is an example of a scintillation crystal.

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