X-ray transmission

Hanke, R. B5bel, F. Determination of material flaw size by intensity evaluation of polychromatic X-ray transmission. NDT-I-E International, Vol. 25(2), 1992, pp. 87-93. 

Considering existing microscopical techniques, one can find that non-destmctive information from the internal stmcture of an object in natural conditions can be obtained by transmission X-ray microscopy. Combination of X-ray transmission technique with tomographical reconstmction allows getting three-dimensional information about the internal microstmcture [1-3]. In this case any internal area can be reconstmcted as a set of flat cross sections which can be used to analyze the two- and three-dimensional morphological parameters [4]. For X-ray methods the contrast in the images is a mixed combination of density and compositional information. In some cases the compositional information can be separated from the density information [5]. Recently there has been a... 

A first example of application of microtomography is taken from life sciences. Here X-ray microscopy and microtomography allows to reconstruct the internal three-dimensional microstructure without any preparation and sometimes even of living objects. Fig. la shows an X-ray transmission microscopical image of bone (femoral head). Several reconstructed cross-sections are shown in Fig.lb. Fig.lc shows the three-dimensional reconstruction of this bone. 

Another application areas of microtomography are biology and agriculture. Fig.4a shows an X-ray transmission image through the tulip bulb in wet conditions. Damaged area can be found in the surface of this bulb. Fig.4b shows the reconstructed cross section with information about depth of damaged volume. 

Instead of monitoring x-ray transmission, some instmments use visible light to monitor concentration (53). This optical technique is generally referred to as turbidimetry or photoextinction. Light is usually used for low particle concentrations and detection of low molecular weight particles. 

Numerous texts and a wealth of literature exist that describe many approaches to X-ray CT imaging. Examples include Refs [2—4]. All approaches involve a large number of X-ray transmission measurements of the item being imaged. In addition to measuring transmission at different positions of the item, all these measurements are then repeated at a large number of different trajectory directions of the incident X-ray beams. 

For in situ x-ray diffraction measurements, the basic construction of an electrochemical cell is a cell-type enclosure of an airtight stainless steel body. A beryllium window, which has a good x-ray transmission profile, is fixed on an opening in the cell. The cathode material can be deposited directly on the beryllium window, itself acting as a positive-electrode contact. A glass fiber separator soaked in liquid electrolyte is then positioned in contact with the cathode followed by a metal anode (3). A number of variations and improvements have been introduced to protect the beryllium window, which is subject to corrosion when the high-voltage cathode is in direct contact with it. 

In another technique know n as X-ray transmission asymmetric crystal topography, changes in defect structure during polymerization of single crystals have been studied. 

In (8) and (9), I is the intensity scattered by one electron, and Sr are the specific surfaces, or surface areas per unit mass of coal, of the macropores and transition pores, respectively the constant C. is proportional to the weak but constant scattering from the micropores b is a constant characterizing the micropore dimensions M and A are respectively the mass of the sample and its cross-section area perpendicular to the incident beam T is the x-ray transmission and a is a constant inversely proportional to the average dimensions of the transition pores. The factor 1/T is included in (9) to take account of the absorption of x-ray in the samples, since (3) was developed under the assumption that the samples were non-absorbing. The transmission T can be expressed—... 

Figure 4.3.6 Principle of two in situ cells that are optimized for the spectroscopic studies and the catalytic experiments the X-ray transmission image is recorded by an X-ray eye, and the calculated profile of the methane concentration is estimated for 1% CH.4/4% 02/He on a pellet of 1 mm thickness and catalyst particles of 100 pm at 500°C (taken from ref. [29]).

FIGURE 7 X-ray transmission through 02 and butane (calculated according to Hoffman et al. (1982)). 

Several of the interesting physical properties of organic conductors (especially transport properties) are expected to be sensitive to crystal defects. It is thus surprising that little has been done up to now to assess crystal quality. For example, a technique that may be used is x-ray transmission topography, a powerful method to obtain information about the internal perfection of not too small crystals, since it provides direct observation of defects. 

The detection system depends mostly on the concentration of absorbing atoms in the material. For bulk x-ray absorption spectroscopy for concentration above 10 atomic ratio standard x-ray transmission techniques are used. Incident and transmitted flux are measured by photoionization chambers. 

A CAT Scanner is a machine designed to collect and process the x ray transmission data required to construct and display a computed axial tomograph. CT scanner is nearly synonymous with CAT scanner, but recognizes that computed views are not hmited to axial views. 

KeV) on samples with concentrations above 10 (atomic ratio), standard X-ray transmission techniques are used. The incident and transmitted fluxes are typically measured by photo-ionization chambers. In the soft X-ray range (i.e., with hv < 1000 eV), absorption spectra may be efficiently measured by recording core-hole decay products. If we describe the inner-shell photo-ionization process as a two-step process, then in the first step the photon excites a core-hole electron pair, and in the second step the recombination process of the core-hole takes place. There are many channels suitable for core-hole recombination. These channels may produce the emission of photons, electrons, or ions, all of which are collected by special detectors. The recombination channel that is normally used to record bulk XAS spectra of dilute systems is the direct radiative core-hole decay that produces X-ray fluorescence lines. When fluorescence lines have high photon energies, this technique probes the bulk. In Figure 4 a beam line with an apparatus to record absorption spectra in the fluorescence mode is schematically represented. 

Fig. 32. Outline of X-ray transmission technique used by Lang 82) to reveal dislocations.

Metal 10% of total Aircraft disk brakes, X-ray transmission windows, space-vehicle optics and instru-usage ments, aircraft/satellite structures, missile parts, nuclear-reactor neutron reflectors,... 

Figure 10. X-ray transmission microscope images taken at the carbon -edge on ALS beam line 6.1.2 showing the macromolecular structure of Suwannee River fulvic acid (from the International Humic Substance Society) in aqueous solution as a function of pH and ionic strength (A pH = 3.0 B pH = 9.0 C pH = 4.0 and [Ca2+] = 0.018 M D pH = 4.0 and [Fe3+] = 0.001 M). The scale bar ion the lower right panel is 800 nm and is representative of the scales in the other panels. [Reprinted with permission from Myneni et al. (1999). Copyright 1999 American Association for the Advancement of Science.)...

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