Scintillators plastic

The plastic scintillators may be considered as solid solutions of organic scintillators. They have properties similar to those of liquid organic scintillators (Table 6.3), but they have the added advantage, compared to liquids, that they do not need a container. Plastic scintillators can be machined into almost any desirable shape and size, ranging from thin fibers to thin sheets. They are inert to water, air, and many chemicals, and for this reason they can be used in direct contact with the radioactive sample. 

Plastic scintillators are also mixtures of a solvent and one or more solutes. The most frequently used solvents are polysterene and polyvinyltoluene. Satisfactory solutes include p-terphenyl and POPOP. The exact compositions of some plastic scintillators are given in Ref. 10. 

Plastic scintillators have a density of about 10 kg/m. Their light output is lower than that of anthracene (Table 6.3). Their decay time is short, and the wavelength corresponding to the maximum intensity of their emission spectrum is between 350 and 450 nm. Trade names of commonly used plastic scintillators are Pilot B, Pilot Y, NE 102, and NE 110. The characteristics of these phosphors are discussed in Refs. 11-13. Plastic scintillators loaded with tin and lead have been tried as X-ray detectors in the 5-100 keV range. Thin plastic scintillator films (as thin as 20 X 10 kg/m = 20 p,g/cm ) have proven to be useful detectors in time-of-flight measurements (see Chap. 13). 

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Oatley and a succession of brilliant students, collaborating with others at the Cavendish Laboratory, by degrees developed an effective instrument a key component was an efficient plastic scintillation counter for the image-forming... 

Radiometric analysis using a plastic scintillator connected to coincidence and anticoincidence circuits (e.g. a Picobeta counter) can be used to detect "Tc. The detection limit is estimated to be about 10 mBq. A slightly better detection limit (1-5 mBq) is reported for a gas flow counter with an anticoincidence shield [8],... 

In a conventional logging apparatus, the scintillation material is comprised of a specially formulated organic polymer or plastic. Many conventional plastic scintillators do not exhibit acceptable mechanical and optical properties when used at relatively high temperature of 75-175°C encountered in a borehole. 

J.J. Simonetti, High temperature plastic scintillators, US Patent 4 713198, assigned to Sangamo Weston, Inc. (Norcross, GA), December 15,1987. 

Systems Using Plastic Scintillators. The lowest backgrounds have been achieved by mounting the sample between 3/4-inch diameter X 1/100-inch thick plastic scintillators. Larger scintillators are used when... 

Very low energy ft particles are not detected by plastic scintillators. This can result in the loss of photopeaks from the p—y coincidence spectrum as illustrated by the spectrum of 134Cs shown in Figure 20. Selfabsorption of the p parti l b tihe fm gglgyesult in similar... 

Many examples of the application of radiotracers to environmental problems exist, and so we have selected only a few of the more interesting ones to discuss. Barry (1971) used 41 Ar, a short-lived gas found in reactor stack effluents, to trace the dispersion of stack effluent from the Chalk River nuclear reactor and relate it to conventional dispersion models. The 41Ar concentrations in the air at various distances from the emitting stack were measured by circulating the air through a counter consisting of layers of plastic scintillator. The (3 particles emitted in the decay of 41Ar were detected by the plastic scintillators. The detectors were... 

When the energy of the charged particle beam is too large to easily stop the beam in a Faraday cup, the beam intensity is frequently monitored by a secondary ionization chamber. These ion chambers have thin entrance and exit windows and measure the differential energy loss when the beam traverses them. They must be calibrated to give absolute beam intensities. If the charged particle beam intensity is very low (<106 particles/s), then individual particles can be counted in a plastic scintillator detector mounted on a photomultiplier tube. 

Since the discovery of luminescence in plastics, the investigation of the action of plastic scintillators has developed rapidly during the last few years. Scintillators based on plastics can be conceived as solid solutions of organic, luminescent substances which are embedded with low concentrations in transparent plastics capable of luminescence. The scintillation mechanism of the system polystyrene— tetraphenylbutadiene was investigated. 

Fig. 1. A magnetic + Si(Li) combination conversion-electron spectrometer based on an "old" Siegbahn-SIStis magnet. 1) beam, 2) target,3) target-changing system, 4) collimator and current measurement, 5) Faraday-cup, 6) Pb shield, 7) anti-positron baffle, 8) detector, 10) cold fingers, 13) cylindrical plastic scintillator 14) light guide, 16) P.M. tube.

We are using a plastic scintillator in our spectrometer. This has the advantage not to get neutron activated, to be a good neutron thermalizer and to yield fast timing signals. It is also relatively cheap. An inorganic scintillator would certainly also perform satisfactorily. 

Coincidence techniques have also been used for Compton interference reduction in the use of large volume Ge(Li) detectors together with plastic scintillator anticoincidence shields 70), In some cases it might be desirable to use the coincidence electronics to gate the multichannel analyzer to accept only non-coincident pulses. In 14 MeV neutron activation procedures the annihilation radiation resulting from the decay of 13N produced indirectly from the carbon in the plastic irradiation unit may be discriminated against by gating the analyzer to accept only non-coincident events. 

Radioisotope detection of P, 14C, and Tc was reported by Kaniansky et al. (7,8) for isotachophoresis. In their work, isotachophoretic separations were performed using fluorinated ethylene-propylene copolymer capillary tubing (300 pm internal diameter) and either a Geiger-Mueller tube or a plastic scintillator/photomultiplier tube combination to detect emitted fi particles. One of their reported detection schemes involved passing the radiolabeled sample components directly through a plastic scintillator. Detector efficiency for 14C-labeled molecules was reported to be 13-15%, and a minimum detection limit of 0.44 nCi was reported for a 212 nL cell volume. 

We report here the design and characterization of three simple, on-line radioisotope detectors for capillary electrophoresis. The first detector utilizes a commercially available semiconductor device responding directly to 7 rays or particles that pass through the walls of the fused silica separation channel. A similar semiconductor detector for 7-emitting radiopharmaceuticals separated by HPLC was reported by Needham and Delaney (XI). The second detector utilizes a commercially available plastic scintillator material that completely surrounds (360 ) the detection region of the separation channel. Light emitted by the plastic scintillator is collected and focused onto the photocathode of a cooled photomultiplier tube. Alternatively, a third detection scheme utilizes a disk fashioned from commercially available plastic scintillator material positioned between two-room temperature photomultiplier tubes operated in the coincidence counting mode. 

Our second on-line radioactivity detector consisted of a plastic scintillator material (BC-400, Bicron Corp., Newbury, OH) that was machined from 1-inch-diameter rod stock into a 5/8-inch-diameter (front face) solid parabola (see Figure 2). A special rotating holder was constructed for the plastic scintillator and the curved outer surfaces were coated by vacuum deposition with a thin film of aluminum in order to reflect the emitted light toward the front face of the scintillator. A detection length of 2 mm was defined within the parabola by aluminum mounting rods (0.250 inch outer diameter) that were press-fit (coaxial to the separation capillary) in the sides of the scintillator, as illustrated in Figure 2. 

Figure 2. Exploded diagram of the plastic scintillator radioisotope detector. The fused silica capillary is exposed to a 2-mm section of the plastic scintillator located between the press-fit aluminum mounting rods.

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