Position sensitive detector curved

Powder diffraction studies with neutrons are perfonned both at nuclear reactors and at spallation sources. In both cases a cylindrical sample is observed by multiple detectors or, in some cases, by a curved, position-sensitive detector. In a powder diffractometer at a reactor, collimators and detectors at many different 20 angles are scaimed over small angular ranges to fill in the pattern. At a spallation source, pulses of neutrons of different wavelengdis strike the sample at different times and detectors at different angles see the entire powder pattern, also at different times. These slightly displaced patterns are then time focused , either by electronic hardware or by software in the subsequent data analysis. 

X-ray measurements were carried out with a small-angle diffractometer with a linear position-sensitive detector. Cu Ka radiation (X = 0.154 mn) was used (Mogilevski et al. 1984). The samples were rotated with respect to the incident beam, while the intensity was registered by linear position-sensitive detector. The angular resolution of the detector was 0.01°. The curves were acquired in the 20 range of 0.3-2.0°. X-ray reflection curves are presented in Figures 22 and 23 for wild-type and recombinant proteins, respectively. The... 

D Position Sensitive Detectors. Position sensitivity is accomplished by a so-called delay line. For every pulse11 arriving at the wire the time is measured that it needs to travel to each of the two ends of the wire. Thus the position of the incident photon along the wire can be computed from the time difference, i.e., the delay. Bent high-resolution ID position sensitive detectors (cf. Fig. 4.14) are advantageously used in laboratory equipment for the recording of WAXS curves. 

Fig. 2. Powder profile of solid C q at atmospheric pressure, measured on a diffractometer equipped with a position-sensitive detector (8) and a 1.5-kW sealed Cu source monochromatized by the (002) reflection of graphite (k = 1.54 A). The powder sample was containol in a Lindemann capillary tube (0.7 mm in diameter). Dots are the measured points (2 hours accumulation), and the solid curve is a least-squares fit to an fee lattice of uniform spherical shells. The best-fit parameters are a = 14.11 A and shell radius Rq = 3.5 A. This sample exhibits much less intensity in the low-angle shoulder of the (111) reflection.

Figure 3.14. The schematic of a powder diffractometer with the vertical goniometer axis, cylindrical sample in the transmission mode and a curved position sensitive detector (PSD). Solid arrows indicate the incident beam and broken arrows indicate the diffracted beams pathways. F - focal point of the x-ray source, M - monochromator, DS - divergence slit, T -incident beam trap.

In principle, curved position sensitive detector can be replaced by a linear position sensitive detector covering segments 5 to 10° (20) wide. This approach considerably increases resolution and decreases Bragg peak widths, but the problem of the enhanced background remains. 

A) Sealed x-ray tube source, curved position sensitive detector, the radius of its goniometer is 150 mm and difflaction data are collected in the transmission mode using cylindrical specimens. You employed this equipment to characterize the phase purity of your materials. 

The powder X-ray diffraction (XRD) patterns were obtained with Cu-Kai radiation on a STOE STADI-P diffractometer equipped with a curved germanium (111) primary monochromator and a linear position-sensitive detector. Typically, the diffractograms were collected at angles 20 between 1 and 10°. 

Figure 2.28 shows a schematic drawing of a Debye-Scherrer device equipped with a curved position sensitive detector. 

These laboratory parallel geometry configurations lead to average angitlar resolutions, but have the advantage of requiring limited acquisition times. Therefore, they are used for apphcations where the acquisition speed is a key factor. From this point of view, they constitute an alternative to the Debye-Scherrer and Hull systems with a curved position sensitive detector, for example, when conducting thermodiffraction measurements. 

A four-reflection monochromator comprised of plane single crystals is placed between the source and the sample (see Figure 2.36). The beam irradiates the sample, which is placed on a three axes sample holder. The sample holder makes it possible to orient the normal to any family of ctystal planes in the diffraction plane defined by the axis of the incident beam and the directions of the diffracted beams. Since the beam is strictly parallel, it is not necessary to inclnde a slit between the sample and the monochromator. The intensity of the diffracted beams is meastrred by using a detector which moves along a circle, centered on the sample or with a curved position sensitive detector. This last featrrre makes this system a distant relative of the Debye-Scherrer diffractometers, for which the sample is, by definition, the center of the detection circle. 

We then produced another diffraction pattern for the same sample with a system equipped with a front monochromator and a curved position sensitive detector [MAS 96a]. The pattern, produced in reflection on a flat plate sample (see Chapter... 

Whichever of these two modes is chosen, this type of incremental measurement necessarily implies long measurement times. An alternative to these methods consists of using a curved position sensitive detector. For each value of the incidence angle to, a direct measurement of the intensity distribution according to 20 is made [BOU 02a, BOU 02c, BOU 04]. This makes the mapping much quicker, between 10 and 100 times shorter more than with a punctual detector. We should point out, however, that this method prohibits the use of analyzer crystals. 

LOU 92] LOUER D., LOUER M., TOUBOUL M., Crystal structure determination of lithium diborate hydrate, LiB203(0h).H20, from x-ray powder diffraction data collected with a curved position sensitive detector , J. Appl. Cryst, vol. 25, p. 617-623,1992. 

MAS 98a] MASSON O., GUINEBRETIERE R., DAUGER A., Profile analysis in asymmetric powder diffraction with parallel beam geometry and curved position sensitive detector . Mater. Sci. Forum, Trans. Tech. Pub., Switzerland, vol. 278-281, p. 115-120,1998. 

STA 92] STAHL K., THOMASSON R., Using CPS120 curved position sensitive detector covering 120°. Powder diffraction data in Rietveld analysis. The dehydration process in the zeolite Thomsonite , J. Appl. Cryst., vol. 25, p. 251-258, 1992. 

SAXS curves were corrected for absorption, air scattering, nonuniformity of the detector sensitivity, slit-length and slit-width smearings as described in detail in our previous paper(5). The WAXD curves were corrected for absorption, air scattering and polarization. The details of the apparatus utilizing the position sensitive detector (PSD) were also described elsewhere(6). 

The X-ray experiments were performed at the EMBL outstation at DESY, Hamburg, as described elsewhere [3-5], using instruments XI3 or X33 equipped with position sensitive detectors (linear or quadrant detectors for details see [8]. Assembly and disassembly were induced by temperature jumps between about 4 and 37 °C (half time 4 to 10 sec) [9]. Reciprocal spacings were calibrated with respect to the collagen reflections from a sample of cornea or tendon. The scattering curves were normalized with respect to the incident intensity measured by an ionization chamber just upstream from the specimen chamber. 

Another important parameter that may affect the resolution is the higher harmonic contribution from the Bragg reflector. A fused quartz mirror behind the monochromator has been currently used to reject this high harmonic contribution. Therefore, the energy resolution of the spectrometer is just limited by the Darwin width of the rocking curve and the spatial resolution of the position-sensitive detector [8]. 

X-Ray diffraction experiments (XRD) are perfonned on a curve position sensitive detector INEL CPS 120 which allows a simultaneous collection of diffracted beams in the range 5° < 2 0 < 125°, with the monochromatized CuKai radiation. Powder samples are manually compacted on windowed aluminum holders. After typically one hour of accumulation, patterns are analyzed with the DIFFAC-AT Siemens software program, a-alumina is used as an internal standard. 

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