X-rays detection

In the x-ray portion of the spectmm, scientific CCDs have been utilized as imaging spectrometers for astronomical mapping of the sun (45), galactic diffuse x-ray background (46), and other x-ray sources. Additionally, scientific CCDs designed for x-ray detection are also used in the fields of x-ray diffraction, materials analysis, medicine, and dentistry. CCD focal planes designed for infrared photon detection have also been demonstrated in InSb (47) and HgCdTe (48) but are not available commercially. 

On-demand beam pulsing has been shown to be effective for eliminating pulse pileup in the X-ray detection system, minimizing the energy dissipated in delicate specimens, yet maximizing the data throughput of the overall system. In essence. 

During World War II and thereafter, the methods of x-ray detection were improved until it is now a matter of simple routine to measure relative x-ray intensity easily and precisely. This improvement, which was accelerated by the rapid progress in nuclear physics, has promoted a rapidly growing appreciation of the great advantages that can attend the application of x-ray absorption and emission to chemical analysis. In their rush to make these applications, analytical chemists have occasionally made discoveries predictable from earlier work, usually by physicists, in the field of x-rays. 

But Roentgen s achievements transcended mere discovery. He studied the properties of the new rays so well that he laid the foundations not only for important methods of x-ray detection (fluorescence of a phosphor, darkening of a photographic plate, ionization of a gas) and for radiography, but for the application of x-ray absorption to analytical cKemistry as well. 

The effects in question are often translated into electric currents, pulsed or continuous. For the convenient reading or recording of these currents, complex electronic circuitry (2.3) may be needed. Modern methods of measuring x-ray intensity are therefore primarily a concern of the experimental physicist. Nevertheless, the analytical chemist must know something about them because x-ray detectors are now among the tools of his trade. This chapter, which cannot hope to do justice to modern x-ray detection, will attempt to provide him with an acceptable minimum of knowledge. 

X-rays being quanta, it follows that the effects used in x-ray detection are quantum effects. In most detectors important in analytical chemistry, these quantum effects eventually yield electrons. Under the simplest conditions, these electrons appear as separate, well-defined pulses (bundles), one pulse for each x-ray quantum. Under these conditions, the pulses can be counted as individuals, and each pulse (hence each x-ray quantum) will register as a unit. As the intensity increases,... 

Above V5. The region of gaseous breakdown, where the catastrophe requires no triggering because the field is higher than the gas can support. Obviously useless for purposes of x-ray detection. 

Cadmium, determination by x-ray emission spectrography, 328 Cadmium sulfide, use in x-ray detection, 43... 

The diffractometer has gradually evolved in terms of maximum power of sealed X-ray tubes, rotating anodes, new X-ray optics, better detector efficiency, position-sensitive detection and, lately, real-time multiple-strip (RTMS) fast X-ray detection, which replaces a single detector by an integrated array of parallel detectors to provide an up to 100-fold increase in efficiency compared with traditional detectors without compromise on resolution. Time-resolved powder diffraction is... 

The specimen chamber (or target chamber) may contain a number of samples and standard specimens mounted on the same sample holder. Also here are the X-ray detection system and a Faraday cup which monitors the proton current incident... 

To determine the Li abundance we considered only 147 slow rotator cluster members, with membership based on radial velocity and X-ray detection. We first... 

Polarization microscopy waves, useful for examining biological material which possesses limited inherent direct contrast Most useful for highly X-ray Detection, localization, and quantitation of... 

The mechanism by which electrons interact with crystals is different from that of X-rays. X-rays detect electron density distribution in crystals, while electrons detect electrostatic potential distribution in crystals. Electron crystallography may be used for studying some special problems related to potential distribution such as the oxidation states of atoms in the crystal. 

Local composition is very useful supplementary information that can be obtained in many of the transmission electron microscopes (TEM). The two main methods to measure local composition are electron energy loss spectrometry (EELS), which is a topic of a separate paper in this volume (Mayer 2004) and x-ray emission spectrometry, which is named EDS or EDX after the energy dispersive spectrometer, because this type of x-ray detection became ubiquitous in the TEM. Present paper introduces this latter method, which measures the X-rays produced by the fast electrons of the TEM, bombarding the sample, to determine the local composition. As an independent topic, information content and usage of the popular X-ray powder dififaction database is also introduced here. Combination of information from these two sources results in an efficient phase identification. Identification of known phases is contrasted to solving unknown stmctures, the latter being the topic of the largest fiaction of this school. 

The discovery of the rare earth elements provide a long history of almost two hundred years of trial and error in the claims of element discovery starting before the time of Dalton s theory of the atom and determination of atomic weight values, Mendeleev s periodic table, the advent of optical spectroscopy, Bohr s theory of the electronic structure of atoms and Moseley s x-ray detection method for atomic number determination. The fact that the similarity in the chemical properties of the rare earth elements make them especially difficult to chemically isolate led to a situation where many mixtures of elements were being mistaken for elemental species. As a result, atomic weight values were not nearly as useful because the lack of separation meant that additional elements would still be present within an oxide and lead to inaccurate atomic weight values. Very pure rare earth samples did not become a reality until the mid twentieth century. 

Bowen JH, Woodward BH, Mossier JA, et al. 1980. Energy dispersive x-ray detection of thorium dioxide. Arch Pathol Lab Med 104 459-461. 

The original and still useful method of X-ray detection is the exposure of photographic film. In the early days of X-ray diffraction, films were also used for the quantitative recording of X-ray intensities. Densitometer measurements of optical density, D, were made of the film. The optical density is defined by... 

Film, photographic -use of amineborane complexes [BORON COMPOUNDS - COMMERCIAL ASPECTS] (V ol 4) -use m x-ray detection [MEDICAL IMAGING TECHNOLOGY] (Vol 16)... 

Doppler velocity may provide a Mossbauer spectrum with a large increase in the signal to noise ratio compared to that obtained in the transmission mode. The type of radiation used to generate the scattered Mossbauer spectrum depends on the internal conversion coefficient a a large value of a, which favors the emission of X rays by the Mdssbauer isotope, makes X-ray detection appropriate, while a small value of a favors y-ray detection. 

More recent support has appeared for the importance of the copper-silicon rich phase on the silicon surface in the MCS reaction. Lieske and coworkers74 showed that redispersion of the eta phase can be an element of the induction period of the MCS reaction and seems to be brought about by the reaction itself. The Cu-Si surface species, perhaps Cu-Si surface compounds or extremely small Cu-Si particles, seem to be of similar importance as X-ray detectable Cu-Si phases. 

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