Scintillation detector materials

The employment of solid scintillation detector materials like thallium-activated sodium iodide detectors for the measurement of gamma radiation... 

Scintillation detectors are substances which fluoresce when stmck by x-radiation. Scintillation can, therefore, serve to convert x-ray photons into visible or ultraviolet light. Scintillation materials include thaUium-activatedcrystals of sodium iodide, NaI(Tl), potassium iodide, KI(T1), or cesium iodide, CsI(Tl) crystals of stilbene (a, P-diphenylethylene) [588-59-0] and anthracene [120-12-7] bismuth germanium oxide [12233-56-6] ... 

Some properties of the detectors most commonly used for transmission experiments are summarized in Table 3.2. Alternative counters are scintillation detectors based on Nal or plastic material that is attached to a photomultiplier, and solid-state detectors using silicon- or germanium-diodes. 

Fig. 3. X-ray diffractogram of Class-F bituminous coal fly ash. Analytical conditions diffraction data were collected using a Philips X-ray powder diffractometer (45 kV/30-40 mA CuKa theta-compensating variable divergence slit diffracted-beam graphite monochromator scintillation detector) automated with an MDI/Radix Databox. The scan parameters were typically 0.02° step size for 1 s count times over a range of 5-60° 2-theta. All data were analysed and displayed using a data reduction and display code (JADE) from Materials Data Inc., livermore, CA.

Gamma-ray spectrometers use scintillator detectors. These spectrometers sense y-rays from all directions, and hence have large "footprints" (commonly hundreds of kilometers diameter) with sizes determined by orbital elevation above the surface. The y-rays come from depths of less than a meter in the target material. 

Solid scintillators include materials such as sodium iodide, lithium iodide, anthracene, naphthalene and loaded polymers. Sodium iodide detectors are by far the most important, and subsequent discussions will be restricted to... 

In the pulse-height distributions of Compton interactions of y-rays in scintillation detectors there are two prominent features usually present (1) the Compton edge, which corresponds to the maximum energy that can be transferred to an electron by the y-ray, and (2) the backscatter peak, which corresponds to the absorption of a photon which has been scattered through 180° in the material surrounding the detector. 

These detectors are made of semiconducting materials. In these detectors, solid-state electrodes are made from Li doped with Si or Ge. The resolution is approximately 1-2 keV for 1 MeV y-Rays and sometimes provides a greater than 10-fold improvement over Nal (Tl) scintillation detectors, described below. These are commercially available and more often used in research-grade instruments. 

The stopping power of the detector determines the mean distance the photon travels until complete deposition of its energy and depends on the density and effective atomic number (ZeU) of the detector material. The scintillation... 

The sensitivity of a PET scanner is defined as the number of counts per unit time detected by the device for each unit of activity present in a source. It is normally expressed in counts per second per microcurie (or megabecquerel) (cps/pCi or cps/kBq). Sensitivity depends on the geometric efficiency, detection efficiency, PHA window settings, and the dead time of the system. The detection efficiency of a detector depends on the scintillation decay time, density, atomic number, and thickness of the detector material that have been discussed in Chap. 2. Also, the effect of PHA window setting on detection efficiency has been discussed in Chap. 2. The effect of the dead time on detection efficiency has been described in Chap. 3. In the section below, only the effects of geometric efficiency and other related factors will be discussed. 

One of the most interesting applications of the HSAB concept consists in the prediction of the stability of the complexes formed owing to interaction of alkali metal halides with rare-earth metal halides. These systems are of great interest for the materials science of scintillation materials the said complex halides are now considered among the most promising scintillation detectors and sensors. Besides, the Li- and Gd-based materials are especially convenient as effective detectors of thermal neutrons. The compositions and stability of the formed compounds depend considerably on the kind of acids and bases from which the compound is formed. So, Li+ cation is one of the hardest cation acids, and, therefore, the formation of stable complex halides of Li and lanthanides according to reaction ... 

For simple gamma counting, thallium-activated sodium iodide [Nal(TI)] scintillation detectors, which became commercially available in the early 1950s, continue to render excellent sen/ices. In spite of the introduction of many other scintillation materials, they remained preeminent. Nal(TI) detectors can be manufactured in various sizes and shapes... 

The most commonly used commercial scintillation detector has a thallium-doped sodium iodide crystal, Nal(Tl), as the scintillating material. A single crystal of Nal containing a small amount of T1 in the crystal lattice is coupled to a PMT, shown in Fig. 8.25. When an X-ray photon enters the crystal, it causes the interaction... 

Gamma and x back-scattering techniques are based upon the Compton photon back-scatter effect. Collimated low-energy gamma rays or X-rays are emitted and beamed at the inspected material. The rays become scattered back toward the detector in direct proportion to the mass of the material in front of the probe. A. scintillation cry.stal detector is used to convert the back-scattered protons into an electrical signal that can be related to material thickness, provided that the material density is constant. Back-scattered. x-rays can be detected by an ariay of scintillation detectors, and the position of the detector relative to the sample relates to different depths in that sample [84]. 

The purified pertechnetate eluted from the column was detected and quantified with a flow through scintillation detector using a lithium glass solid scintillator. This scintillator material exhibited excellent stability in the strong nitric acid solutions used for pertechnetate elution. 

Not very advanced compared with PRDs, hand-held survey meters can be used to detect the location of the radioactive material. These meters could be engineered to possess interchangeable probes consisting of scintillation detectors and phototubes, and large-volume ionization chambers or neutron detectors. ... 

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