Scintillator phosphors

Scintillation counters are constructed by coupling a suitable scintillation phosphor to a light-sensitive photomultiplier tube. Figure 25 illustrates an example of a scintillation counter using a thallium-activated sodium iodide crystal. 

There are three classes of solid state scintillation phosphors organic crystals, inorganic crystals, and plastic phosphors. 

Organic scintillation phosphors include naphthalene, stilbene, and anthracene. The decay time of this type of phosphor is approximately 10 nanoseconds. This type of crystal is frequently used in the detection of beta particles. 

A schematic cross-section of one type of photomultiplier tube is shown in Figure 26. The photomultiplier is a vacuum tube with a glass envelope containing a photocathode and a series of electrodes called dynodes. Light from a scintillation phosphor liberates electrons from the photocathode by the photoelectric effect. These electrons are not of sufficient number or energy to be detected reliably by conventional electronics. However, in the photomultiplier tube, they are attracted by a voltage drop of about 50 volts to the nearest dynode. 

A brief review of scintillation phosphors and their uses are given in Table 4. 

CAS 3073-87-8. C6H4[C3NO(CH3)C6H5]2. Yellow needles with a bluish fluorescence, mp 231-234C. Use As a scintillation phosphor. 

Scintillators used for y-ray detection from TC43 (141 kev), kev) and Tlgi (75 kev), include NaI Tl and Bi GCgO available in 80 cm single-crystal plates, a form not easily achieved by other scintillator phosphor compositions. 

Rodnyi PA, Dorenbos P, Vaneijk CWE (1994) Creation of elecron-hole pairs in inorganic scintillators. In Weber MJ, Lecoq P, Ruchti RC, Woody C, Yen WM, Zhu RY (eds) Scintillator Phosphor Mater pp 379-385... 

Finally, with their spatial resolution only limited by the channel dimensions and the spacing between channels (typically both of the order 10—20 pm), they are ideally suited for imaging applications. For this, the electron flux exiting from the MCP impinges on a scintillator (phosphor) plate, which in turn is coupled to a 2D CCD sensor recording the spatial distribution of the scintillator excitation. All three components are mounted in close proximity to maintain the micrometre resolution, as shown in Figure 13.14c. Such detectors are used in the electron-and ion-imaging experiments described, for example, in Chapter 23. 

The aim with a scintillator detector is to combine the neutron absorbing element intimately with a scintillating phosphor so that the reaction products from the capture of a neutron strike the phosphor and produce a light flash, which is then detected by a photomultiplier tube (see Figure 4B). 

In all this early work, the x-ray beam impinged upon a phosphor powder on the tube envelope. Detectors of this general kind will be called phosphor-photoelectric detectors to distinguish them from modern scintillation counters (2.11), also photoelectric, in which the light is often generated in a single crystal. The name phosphor-photoelectric detector/ though necessary, is clumsy and not entirely satisfactory. 

In the phosphor-photoelectric detector used as just described, the x-ray quanta strike the phosphor at a rate so great that the quanta of visible light are never resolved they are integrated into a beam of visible light the intensity of which is measured by the multiplier phototube. In the scintillation counters usual in analytical chemistry, on the other hand, individual x-ray quanta can be absorbed by a single crystal highly transparent to light (for example, an alkali halide crystal with thallium as activator), and the resultant visible scintillations can produce an output pulse of electrons from the multiplier phototube. The pulses can be counted as were the pulses-from the proportional counter. 

A scintillation counter makes use of the fact that phosphors—phosphorescent substances such as sodium iodide and zinc sulfide (see Section 15.14)—give a flash of light—a scintillation—when exposed to radiation. The counter also contains a photomultiplier tube, which converts light into an electrical signal. The intensity of the radiation is determined from the strength of the electronic signal. 

KL-HDEHP = 50% di(2-ethylhexyl) phosphoric acid, 60-100 mesh resin PERALS = Photon/electron rejecting alpha liquid scintillation TNOA = tri-n-octylamine TRU = transuranic... 

Counter, Scintillation—The combination of phosphor, photomultiplier tube, and associated circuits for counting light emissions produced in the phosphors by ionizing radiation. Scintillation counters generally are more sensitive than GM counters for gamma radiation. 

The suppression and recovery of protein synthesis from DTT treatment (without cycloheximide treatment) can be monitored via metabolic pulse radiolabeling of cell cultures using [35S]-methionine and subsequent determination of radiolabeled protein content either by SDS-PAGE/ phosphor-imager analysis or liquid scintillation of tricholoroacetic acid insoluble material (Stephens et al., 2005). 

The scintillation counter is a solid state radiation detector which uses a scintillation crystal (phosphor) to detect radiation and produce light pulses. Figure 24 is important in the explanation of scintillation counter operation. 

Plastic phosphors are made by adding scintillation chemicals to a plastic matrix. The decay constant is the shortest of the three phosphor types, approaching 1 or 2 nanoseconds. The plastic has a high hydrogen content therefore, it is useful for fast neutron detectors. 

A radioactivity detector is used to measure radioactivity in the HPLC eluent, using a flow cell. The detection principle is based on liquid scintillation technology to detect phosphors caused by radiation, though a solid-state scintillator is often used around the flow cell [17,31]. This detector is very specific and can be extremely sensitive. It is often used for conducting experiments using tritium or C-14 radiolabeled compounds in toxicological, metabolic, or degradation studies. 

Equipment PCR machine, scintillation counter, tabletop centrifuge, temperature-controlled water baths, equipment for horizontal and vertical electrophoresis, UV-illuminator, phosphor imager, automatic DNA sequencer, vacuum dot-blot manifold (Schleicher and Schuell). PCR 0.5 ml hot-start mbes, aerosol resistant pipette rips, autoclaved Eppendorf tubes (all from Fischer Scientific, Brightwaters, NY) and glassware, diethyl pyrocarbonate (DEPC, Sigma)-treated solutions. 

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