Scintillation single crystal

B. G. Zaslavsky, Automated Pulling of Large-Diameter Alkali Halide Scintillation Single Crystals from the Melt, J. Cryst. Growth 200 (1999) 476-482. 

The ability of high-temperature ionic solvents to dissolve various substances (e.g. metals or their oxides) is considered among their most important characteristics. In the case of scintillation, single crystals based on alkali-metal halides, some halides-dopants (Til, CeX3, etc.), are available as admixtures since they create levels in the forbidden zone which are responsible for the scintillation. In contrast, oxygen-containing admixtures are harmful since their existence in the crystals causes a considerable reduction in their light-yield, radiation resistance, etc. 

Cerium is one of the most widely used activators, which improve the working characteristics of many scintillators. Determination of the valence state of cerium in single crystals of alkaline and rare-earth borates allows to establish the nature of activator centers for purposeful influence on the scintillation efficiency of the matrix. 

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. 

The basic instrumentation used for spectrometric measurements has already been described in the previous chapter (p. 277). Methods of excitation, monochromators and detectors used in atomic emission and absorption techniques are included in Table 8.1. Sources of radiation physically separated from the sample are required for atomic absorption, atomic fluorescence and X-ray fluorescence spectrometry (cf. molecular absorption spectrometry), whereas in flame photometry, arc/spark and plasma emission techniques, the sample is excited directly by thermal means. Diffraction gratings or prism monochromators are used for dispersion in all the techniques including X-ray fluorescence where a single crystal of appropriate lattice dimensions acts as a grating. Atomic fluorescence spectra are sufficiently simple to allow the use of an interference filter in many instances. Photomultiplier detectors are used in every technique except X-ray fluorescence where proportional counting or scintillation devices are employed. Photographic recording of a complete spectrum facilitates qualitative analysis by optical emission spectrometry, but is now rarely used. 

Scintillation counters are used to detect energy-rich particles and y rays. They consist of a combination of a phosphor, usually a single crystal, with a photomultiplier or a photodiode as detector. Alkali-metal iodides (see Table 56), Bi4Ge3012, CaW04, ZnW04, CdW04, and ZnS Ag+, Ni+ are typical phosphors for this application [5.438]. 

The same data collection and reduction techniques are commonly used by the same workers for many different polymers. Therefore, data for these other polymers may contain errors on a similar scale, but that the errors have usually, but not always, gone undetected (8). If more than 500 reflections are observed, from single crystals of simple molecules, recognizable electron-density distributions have been derived from visually estimated data classified only a "weak", "medium" or "strong". The calculation of the structure becomes more sensitive to the accuracy of the intensity data as the number of data points approaches the number of variables in the structure. One problem encountered in crystal structure analyses of fibrous polymers is that of a very limited number of reflections (low data to parameter ratio). In addition, fibrous polymers usually scatter x-rays too weakly to be accurately measured by ionization or scintillation counter techniques. Therefore, the need for a critical study of the photographic techniques of obtaining accurate diffraction intensities is paramount. 

X-ray fluorescence fluorescence emission X-radiation cell single crystal diffractor gas ionization, crystal scintillation or semiconductor... 

Intensity results were collected on a General Electric XRD-5 Spectrogoniometer, equipped with a Single Crystal Orienter and scintillation counter, with use of Cu-/fg radiation (nickel filter and pulse-height analyser). Complete three-dimensional measurements were recorded for 6 74° (corresponding to a minimum interplanar spacing d = 0-80 A), and all 193 independent reflections in this range were measurable. The intensities were corrected for... 

Semiconductor detectors, made from single crystals of very pure germanium or silicon, are the highest performance detector type. The superior resolution of these detectors has revolutionized data-gathering for X-ray and gamma-ray measurements. The comparison of the pulse resolving ability of the three types of X-ray detectors scintillator, gas proportional and Si(Li) is shown in Fig. 5.18. 

Beta (fl) Single crystals of anthracene, rranj-stillbene are commonly used. Sometimes naphthalene doped with anthracene can also be used. For P-Particle counting, especially low-energy particles from and tritium, liquid scintillators are commonly used (see discussion below on liquid scintillators). 

O. G. VIAGIN, V. K. KLOCHKOV, A. A. MASALOV, Yu. V. MALYUKIN Institute for Scintillation Materials, STC "Institute for Single Crystals" NASU Lenin Ave. 60, 61001 Kharkiv, Ukraine... 

Use Polymerized with styrene to make a plastic phosphor. Single crystals used as scintillation counters. 

Early powder diffraction experiments relied mostly on the Debye-Scherrer experiment to record a diffractogram. A broad film strip set into a cylindrical chamber produced the first known two-dimensional powder diffraction data. In contrast to modern methods the thin equatorial strip was the only part of interest and intensities merely optically and qualitatively analysed. This changed drastically with the use of electronic scintillation counters. Intensities were no longer a matter of quality but quantity. Inevitably the introduction of intensity correction functions long known to the single-crystal metier, i.e. Lorentz and polarization corrections (see Section 14.3), made their way into the field of powder diffraction. 

Although Nd YAG requires large, defect-free single crystals [89], polycrystalline ceramics are cheaper to manufacture and there is increasing use of YAG ceramics [90] as scintillators for radiation detection, for example Ce-doped YAG ceramics [91, 92], In this case, the luminescence comes both from the activation of the Ce ion, with additional UV contribution, and from the YAG host itself. 

B.G. Zaslavsky, Distinctive Features of Automated Pulling of Large Scintillation Alkali Iodides Single Crystals without Oxygen-Containing Impurities, J. Cryst. Growth 218 (2000) 277-281. 

Yu.F. Rybkin and V.V. Banik, Acid-Base Interactions in Molten Sodium Iodide, in Methods of Obtaining and Investigations of Single Crystals and Scintillators, N5 (Institute for Single Crystals, Kharkov, 1980) pp. 121-125. 

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