Scintillation detector construction

Existing liquid scintillator detectors constructed about 50 m.w.e. (20 m of rock) below the surface could detect 1 kt tests a few kilometers from a source and therefore could be useful for the first two applications. The utility of such a detector ultimately depends on trade-offs between cost and the desire by states for a non-intrusive local nuclear monitoring system. 

This report describes the construction and operation of an automated gauge designed to measure the quantity of propint powder sealed within 40-mm cartridges at a production rate of one per second. The measurement technique employs the back-scattering of low energy gammas from 241 Am, a scintillation detector and... 

The one-dimensional angular correlation spectrometer is a relatively simple equipment (O Fig. 27.4). It is constructed from two scintillation detectors, several slits, a coincidence unit, and a storage unit. 

DCEMS together with low-temperature and in-field measurements require much more sophisticated experimental equipment. Gas counters, scintillation detectors, electron multipliers (Channeltron, Ceratron), surface barrier silicon semiconductor detector, and electron energy analyzers belong to the most frequently used detectors applied in CEMS and CXMS, respectively. Differences among individual constructions can be found in Ref. 123. Commercially available version of CEMS/CXMS spectrometer is depicted in Fig. 18.36 [127]. Device is based on 27t proportional continuous gas flow counter for room-temperature zero-magnetic field measurements. 

If we are to construct a scintillation detector for gamma-ray detection and spectrometry, the scintillator material must have a number of particular properties ... 

Figure 21.15 shows a patient undCTgoing a PET scan of the brain. The instrument actually detects gamma radiation. When a nucleus emits a positron within the body, the positron travels only a few millimeters before it reacts with an electron. This reaction is an example of the annihilation of matter (an electron) by antimatter (a positron). Both the electron and the positron disappear and produce two gamma photons. The gamma photons easily pass through human tissue, so they can be recorded by scintillation detectors placed around the body. You can see the circular bank of detectors in Figure 21.15. The detectors record the distribution of gamma radiation, and from this information a computer constructs images that can be used by the physician.

Sn, 1 1 Eu, 1 1 Dy and i Tm. Second, scintillation detectors may be considered. Thin organic (crystal or plastic) scintillators are used for detecting electrons. Gas scintillation proportional counters with a good energy resolution (e.g. R 8% at 6 keV) may also be constructed for CEMS as well as semiconductor detectors. 

Scintillation detector probes should not be exposed to over 30 degrees Centigrade because the photocathode might deteriorate. Never leave the scintillation detector, for example, in a car with closed windows. The mechanical construction might survive high accelerations, but this should be avoided if possible. 

Various computed tomography CT- scanners for industrial applications have been designed and constructed) They use as radiation sources X-ray tubes or gamma emitting radioisotopes and as detectors NaI(Tl)-scintillators for gamma rays and image intensifiers for X-rays. 

To reduce interference from Compton scattering, an anticoincidence shield, 76 cm. X 76 cm., was constructed as shown in Figures 2 and 3. The shield consists of two independent type NE-102 plastic phosphor annuli. A 10-cm. bore through the top annulus accommodates the Ge(Li) detector chamber and the cryogenic assembly. The bottom annulus (i.d. diameter 25 cm.) houses a 20-cm. diameter by 15-cm. thick Nal(Tl) scintillator. Normally, the plastic phosphor is used in conjunction with the Nal(Tl) to form a well -shaped anticoincidence shield. Altema-... 

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. 

Because a 2-D photon-counting detector was not available at the time of construction of the demonstrator, the detector was realized as a single 1-D vertical detector column based on scintillator crystals and photomultipliers, which can be rotated around the focus point, thereby acquiring one projection. Spatial resolution was ensured by a collimator made of thin tungsten lamellae placed in front of the detector. 

The choice of detector is determined by the radionuclide to be assayed and the required temperature of operation. A paper by Cacace compared Geiger-Muller counters, internal flow proportional counters, scintillation counters, and ionization chambers. Perhaps the simplest to use, in conjunction with a chromatographic column, is the internal flow proportional counter, which has considerable advantages for the detection of [14-C] and [3-H]. ° Schmidt-Bleek and Rowland have described a counter, constructed of brass and Teflon with a stainless-steel anode, which is very robust, inert... 

With phoswich type rejection in the scintillator, escape-gating rejection in the gas detector together with risetime discrimination and the possibility of mutual rejection between the two sections, the hybrid offers broad-band high-sensitivity coverage which greatly improves the standard phoswich for little added complexity. A 1/2 scale prototype is under construction to resolve remaining design questions [16]. 

Such neutron detectors are simple to construct. For purposes of pulse height calibration, it is desirable to avoid leaving the photomultiplier surface in contact with the scintillating liquid. 

In photomultiplier-based detectors, the incoming ion beam is first converted to a photon beam when ions strike a scintillation material. The emitted photons are amplified and detected by a conventional photomultiplier. The construction of a photomultiplier is similar to that of an EM, except that the conversion dynode, called the photocathode, is coated with a photoemissive material that emits electrons when struck by photons. Photomultipliers are usually employed in combination with postacceleration devices, which are discussed next. 

The TOP wall, BT, is the furthest downstream detector in the sequence. Although the original plans called for this detector to be built from existing scintillators, an investigation of the detector elements at CMU has shown serious problems due to crazing and breaks in the scintillator material. As a result, new scintillation material has been purchased and a totally new detector system is being constructed by a collaboration of Manitoba, KEK, and CMU, The components are scheduled to be shipped to the AGS August for assembly. 

The main components of the detector are 1) An assembly of 40 scintillator elements (200cm X 8.5 cm X 5 cm) airangea in a staggered array of two layers 10 cm apart. These are being bought by the Univ. of Kyoto from Bicron Corp. 2) Eighty Hamamatsu photomultiplier tubes and bases supplied by the University of Kyoto Sangyo. 3) An assembly and elevation stand. This is now under construction at TRIUMF. 

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