Radiation white

Fig. 5—6. Geiger-counter output currents recorded by Dow automatic x-ray absorption spectrometer. Superposed records on left are x-ray absorptiometric curves for iso-octane and a solution containing ethylene dibromide, whereas traces at right illustrate recording of transmitted intensities at fixed wavelengths. Apparent change in x-ray absorption of solvent in going through bromine absorption edge is result of marked slope of white radiation distribution curve at 0.9 A. 16 (Liebhafsky, Anal. Chem., 21, 17. Courtesy of Dow Chemical Company.)...

In practice, the continuum ( white ) radiation causes difficulties when X-ray tubes are used as sources in chemical analysis because continuous... 

Figure 10.5 Real-time image, with no computer processing, of magnetic domains and low-angle boundaries in iron-silicon taken using the Bede Scientific HI-RES detector at Daresbury Laboratory. The white radiation topograph was taken with X-rays of fundamental wavelength 1 A...

Figure 10.6 White radiation topography with synchrotron radiation...

White radiation topography has the following special features ... 

Figure 10.12 White radiation topographs of 90° antiferromagnetic domain walls in KN1F3 under conditions of increasing magnetic field, (a) 0.27T, (b) 0.46T (c) 0.64T...

The Laue method (using white radiation) has not yet been used for a de novo virus structure determination. Whilst this method continues to have potential for stud)dng d)mamic events it compounds the problem of spot resolution and will only be feasible with detectors with greater resolution than is furnished by current CCD detectors. 

The spectrum of emissions from a water-cooled anode X-ray tube consists of (i) characteristic lines and (ii) a background "white radiation" called Bremsstrahlung, or braking radiation. 

The alternative is to vary the size of the Ewald sphere (i.e. the wavelength) until it touches a reciprocal lattice point. In practice, this is achieved by using an incident beam of white radiation with a continuous spectrum of wavelengths. Historically, this was the first X-ray technique (Lane method), later eclipsed by methods using monochromatic radiation but recently resurgent with the introduction of image plate detectors (see below). 

Filter is a thin film of a metal immediately, or closely, preceding the target element in the periodic table, for example, Ni for Cu target, Zr for Mo target. Thus the absorption edge of the filter metal falls between the K and lines and effectively removes the latter, but not the white radiation. Filters lose very little of the Ka intensity compared to monochromators, but are inferior to the latter in spectral purity of the resulting beam. 

Xa.,W20j.2H.,0 is obtained as white radiating crystals by the addition of hydrogen peroxide to a hot solution of sodium paratungstate and evaporation of the mixture in a vacuum. The crystals are easily soluble in water. 

There are three accessories used to produce monochromatic radiation metal foil filters, crystal monochromators, and focusing mirrors. An element with atomic number Z can be used as a selective filter for radiation produced by an element of atomic number Z+ 1. For example, a nickel (Z=28) absorption filter, may be used to cut out the Cu KjS (Z=29 for Cu) radiation, leaving only Cu Ka radiation.Not all white radiation, however, is eliminated by this method. Alternatively a single-crystal monochromator may be used. An intense Bragg reflection from the monochromator crystal is used as the incident beam for X-ray diffraction studies. Focusing mirrors, designed to produce a beam that is not only monochromatic but also convergent, may be used. In this case the incident beam is doubly deflected by two perpendicular mirrors. 

A Laue photograph -is produced by irradiating a stationary crystal with a beam of X rays that has a wide range of wavelengths ( white radiation). It differs from all of the other methods for collecting diffraction data in that the crystal is stationary throughout the experiment. Diffraction is therefore dependent on the multiwavelength feature of the... 

White radiation Any radiation, such as X rays or sunlight, with a continuum of wavelengths. 

Nelmes, R. J. Removal of the white radiation background from data collected with / -filtered MoKa and AgKa X rays. Acta Cryst. A31, 273-279 (1975). 

FIGURE 8.24. A view of (a) potash alum (transparent) growing on a single crystal of isomorphous chrome alum (purple interior). Diffraction photographs of (b) potash alum and (c) chrome alum. The radial streaks are from white radiation and can be ignored. Note some differences in intensity. The arrows indicate two differences that are visible to the naked eye. (Photographs courtesy Maria Flocco and Henry Katz.)... 

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