Position-sensitive area detectors

Photon counting devices are required in order to arrive at the necessary accuracy. The noise of the detector has to be lower than 4 orders of magnitude with respect to the signal. Our experience with multiwire proportional chambers may let us believe that this rather stringent condition can be fulfilled. The simultaneous measurement of the whole scattering pattern by position sensitive area detectors is absolutely mandatory... 

Static SAXS experiments were performed on the Oak Ridge National Laboratory 10-m pinhole collimated SAXS camera using CuK radiation (X. = 0.154 nm) and a 20 x 20 on position-sensitive area detector. The scattering from each sample was determined at two sample-to-detector distances 2.119 and 5.119 m. The data were azimuthaiiy averaged and converted to an absoiute differential cross-section by means of precalibrated secondary standards (6) a high density polyethylene, PES-3, was used for the low q data and a vitreous carbon standard was employed for the... 

When the copolyester is heated up or cooled down in the liquid crystalline state fluctuations in the scattering intensity can be observed. Fig. 56 shows the intensity obtained by a position sensitive linear detector and integrated from 29 = 12° 26 = 30° as a function of time. Obviously, the time scale of the fluctuations lies in the region of minutes. Measurements at different azimutal angles reveal that the fluctuations are caused by changes in the orientation of the chains. The area of the film from which the scattering arises is about 2 mm x 2 mm. 

The MAPS spectrometer at ISIS [2], Fig. 12.1(a), is a third generation instrument that demonstrates the future direction of direct geometry instruments. The principal innovation is the use of large area, position sensitive He detectors ( 3.3.1.1). An area of 16 m. Fig. 12.1(b), of the sample environment tank is covered by 576 detectors that provide ahnost continuous coverage over a large solid angle in the forward scattering direction. 

Figure Bl.23.10. Schematic diagram of a scattering and recoiling imaging spectrometer (SARIS). A large-area (95 X 75 nnn ), time-resolving, position-sensitive microchannel plate (MCP) detector captures a large...

CCD detector consists of 224 linear photodetector arrays on a silicon chip with a surface area of 13 x 18 mm (Fig. 4.16). The array segments detect three or four analytical lines of high analytical sensitivity and large dynamic range and which are free from spectral interferences. Each subarray is comprised of pixels. The pixels are photosensitive areas of silicon and are positioned on the detector atx -y locations that correspond to the locations of the desired emission lines generated by an echelle spectrometer. The emission lines are detected by means of their location on the chip and more than one line may be measured simultaneously. The detector can then be electronically wiped clean and the next sample analysed. The advantages of such detectors are that they make available as many as ten lines per element, so lines which suffer from interferences can be identified and eliminated from the analysis. Compared with many PMTs, a CCD detector offers an improvement in quantum efficiency and a lower dark current. 

The identification of the first transuranium elements was by chemical means. In the early 1960s physical techniques were developed which allowed for detection of nuclei with lifetimes of less than one second at high sensitivity. A further improvement of the physical methods was obtained with the development of recoil separators and large area position sensitive detectors. As a prime example for such instruments, we will describe the velocity filter SHIP (Separator for Heavy-Ion reaction Products) and its detector system, which were developed at the UNILAC. The principle of separation and detection techniques used in the other laboratories is comparable. 

Zavalij, 2003). Position-sensitive detectors (also called area detectors), based either on a gas-filled ionization chamber or an image intensifier coupled to a video camera detect and record diffraction beam intensity in two dimensions simultaneously, a feature that greatly enhances the speed of data collection (Drenth, 1999). 

Semiconductor detectors have supplanted all other point detectors during 1980s, soon to be superseded by position-sensitive detectors (PSDs) alias area detectors, which can... 

As already mentioned, area (or position sensitive) detectors were first developed for neutron crystallography, since neutrons are scarce and expensive and it is important both to shorten the experiment and to use aU neutrons scattered by a sample in various directions, rather than waste all but one reflection at a time. Besides 2D scintillation detectors, there are banana ID multiwire detector and 2D detectors with two mutually perpendicular sets of parallel wires. The latter design is usefiil for time-of-ffight experiments because of ideal time resolution once an ioiuzation discharge induces current in one or more wires, we instantly know both the place and time of its arrival. 

Electronic Position Sensitive Detectors, linear and area detectors, make the collection of the information contained in diffraction or scattering patterns highly efficient. 

Figure 3.59. Top and side-view of the experimental set-up for grazing incidence X-ray diffraction measurements on Langmuir monolayers. The footprint of the Incident beam is indicated by the darker area. Only the crossed-beam area ABCD contributes to the detected scattering. The Seller eollimator selects a horizontal scattering angle of 20 the position-sensitive detector (PSD) has its axis vertical and measures the Bragg rod profiles. In this geometry one has the ability to determine the lateral (q ) as well as the vertieal (q ) components of the scattering vector. (Redrawn from J. Als-Nielsen and K. KJaer, loc. clt.

The area detector - is an electronic device for measuring many diffracted intensities at one time. It is an electronic substitute for film, and is now used, where possible, for crystals of biological macromolecules. It is a position-sensitive detector, and is coupled to an electronic device for recording the data in computer-readable form. The data so recorded include the intensity of a Bragg reflection (diffracted beam) and its precise direction (as a location on the detector). Both types of information are needed for each Bragg reflection so that I(hkl), and sinO/X can be determined. 

Area detector A position-sensitive electronic device for meMuring the intensities of a large number of diffraction data at one time in two dimensions. It gives information on both the direction and intensity of each diffracted beam. By analogy, it might be called electronic film. 

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