Two-dimensional position-sensitive

The photolysis of aromatic species with tetranitromethane in perfluoro alcohol solvent has been studied, in which the radical cations were observed by EPR spectroscopy.284 Photo-stimulated reaction of 1- and 2-haloadamantanes and 1,2- and 1,3-dihaloadamantanes with various carbanionic nucleophiles afforded products rationalized through an SrnI mechanism.285 286 Photolysis of the cycloadduct formed between a functionalized derivative of C6o and diazomethane has been shown to afford a pah of ling-opened structures (125) and (126) via a proposed biradical intermediate (127) (Scheme 19). The UV-photolytic fragments of /-butyl iodide (T and /-Bu ) have been ionized by resonance-enhanced multiphoton ionization for TOF mass spectro-metric analysis.287 A two-dimensional position-sensitive detector provided angular distribution and translational energy data. 

Fig. 1. Principle of the set-up for the pion mass experiment consisting of the cyclotron trap with a gas cell and a curved-crystal spectrometer equipped with a two-dimensional position-sensitive X-ray detector. The focusing condition for a wave length A reflected under the Bragg angle Ob is R-sin B, where R is the (horizontal) radius of curvature. Typical values for R and the diameter of the spherically bent crystals are 3 m and 100 mm...

There is more. Tonomura reports experiments on electron interference using field-emission electron microscope equipped with an electron biprism and two-dimensional, position-sensitive, electron-counting system [12]. Events could be counted one-by-one on a TV monitor. Let us describe some results from the present perspective. 

In addition to the standard discussion of the materials studied, and processing and analytical techniques employed for this work, a rather lengthy presentation on two-dimensional position sensitive detectors for SALS will be presented. A review of prior work performed by other researchers will be discussed, as well as the particulars of the detector developed for this study. Finally, a comparison between the detector presented here, and those developed previously will be made. 

Two-Dimensional Position Sensitive DACecCor, Calibration. A number of tests were performed to assure the accuracy ot the data collected by the system. These Included testing the detector uniformity to Insure that all the photo-diodes on the chip are of equivalent sensitivity. Another calibration of the device was to determine the magnifying affects of the camera. This was done to allow conversion of the x-y pixel grid Into the dimensions of reciprocal space. Finally, the contrast setting was adjusted so that a S6 value of 0 was produced when the screen was not Illuminated, with the gain set at maximum and the f-stop wide open. Further details of the system calibration can be found In Effler s M.S. thesis (17). 

SAXS measurements were made at the National Center for Small Angle Scattering Research (NCSASR) at Oak Ridge National Laboratory using the 10m SAXS camera. The instrument used a rotating anode CuK (X" 0.1542 nm) x-ray source, crystal monochromatization of the incident beam, pinhole collimation, and a two dimensional, position sensitive, proportional counter. Sample to detector distance was 1.12 m. Disc-shaped samples were cut from the molded films and dried in a vacuum oven at 65 °C for four weeks prior to the SAXS analyses. 

GAB 78] GABRIEL A., DAUVERGNE F., ROSENBAUM C., Linear, circular and two dimensional position sensitive detectors , Nucl. Instrum. Meth., vol. 152, p. 191-194,1978. 

The area detector is an electronic device for measuring many diffracted intensities at one time. It is a two-dimensional, position-sensitive detector that records the intensity of a Bragg reflection (diffracted beam) and its precise direction (as a location on the detector) it acts like an electronic substitute for film. This detection device is now used extensively for crystals of biological macromolecules. Such a detector may involve a multiwire proportional counter coupled to an electronic device or a television imaging system both devices permit a recording of the data in a computer-readable form. Alternatively, imaging plates may be used. These have phosphorescent material layered on them and store information on the extent of X-ray exposure until scanned bv a laser, when the intensity and location of the light then emitted is recorded. 

If the scattering patterns are anisotropic due to a preferred orientation of molecules and crystals, it is often desirable to use two-dimensional position sensitive counters. Such area detectors, based on the principles described above, are the multiwire proportional counters (MWPC). A number of parallel tightened anode wires are mounted in front of a cathode structure, the latter consisting of two layers of parallel metal strips which are oriented horizontally in one layer and vertically in the other. One possibility of reading out the strips is to connect the strips of each... 

Various multiwire proportional counters (MWPC) have been designed for use as two-dimensional position-sensitive detectors. An example of such a design is illustrated in Figure 2.17. Here a plane of fine, equally spaced parallel wires functions... 

Figure 2.17 Schematic of a two-dimensional position-sensitive multiwire proportional counter (MWPC). (The spacing between electrode planes is not to scale.)...

TCSPC with two-dimensional position-sensitive detection can be used to acquire time-resolved images with wide-field illumination. The complete sample is illuminated by the laser and a fluorescence image of the sample is projected on the detector. For each photon, the coordinates in the image area and the time in the laser pulse sequence are determined. These values are used to build up the photon distribution over the image coordinates and the time (see Fig. 3.12, page 40). The technique dates back to the 70s [312] and is described in detail in [262]. Lifetime imaging with a TCSPC wide-field system and its application to GFP-DsRed FRET is described in [162]. A spatially one-dimensional lifetime system based on a delay-line MCP is described in [509]. 

M. Lampton, C.W. Carson, Low-distortion resisitive anodes for two-dimensional position-sensitive MCP systems, Rev. Sci. Instrum. 50, 1093-1097 (1979)... 

In comparison with film cameras, diffractometers are roughly a factor of 10 more costly. They are still more expen.sive if the point counter is replaced by a one- or two-dimensional position-sensitive detector. The data acquisition time is, however, shortened by a factor of 50-100, or even more, depending on the geometry of the crystal lattice measured. 

The Digital Autoradiograph (DAR) LB 287, a two-dimensional, position-sensitive, multiwire proportional counter detector, was discontinued by Berthold, but the instrument is still being used in many analytical laboratories, and papers are published regularly citing its use. The DAR is described in Chapter 13 of the previous edition of this book. 

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