Proportional counter position-sensitive

Lower tolerance to P radiation than ionization chamber or proportional counter. Greater sensitivity to sample size, and position. 

Specific detectors are also available for quantification of radiopharmaceuticals. These detectors use a position-sensitive proportional counter. These detectors are sensitive to the beta and gamma nuclides listed in Table 3.5. The detector analog output can also be represented as an analog curve. Various other detection procedures have also been used, such as flame ionization [66], mass spectrometry [27,67], and infrared (IR) [68,69]. 

Figure 22.4. Schematic diagram of a synchrotron X-ray diffractometer. PSPC position sensitive proportional counter SR beam synchrotron radiation beam. (Reproduced with permission from Ueno et al., 2000.)...

The Diethorn expression has been applied in a detailed analysis of commercially available proportional chambers by R. W. Hendricks Fig. 2 shows the test results for a series of counters, the parameters of which are given in Table I. The tested devices are not position sensitive detectors, but normal cylindrical proportional counters. 

A specific type of proportional counter that is used for accurate counting of a and P activity on smear samples, is the gas flow proportional counter. In some types of gas flow proportional counters, the sample is put inside the detector for greater sensitivity—there is no structural material to absorb the radiation before it can be detected. Figure 5.24 shows a diagram of the detector of such a gas flow proportional counter. Other gas flow proportional counters have very thin Mylar windows sealing off the detector s gas chamber. During counting, samples are positioned very close to the window. 

A position sensitive detector (PSD) employs the principle of a gas proportional counter, with an added capability to detect the location of a photon absorption event. Hence, unlike the conventional gas proportional counter, the PSD is a line detector that can measure the intensity of the diffracted beam in multiple (usually thousands) points simultaneously. As a result, a powder diffraction experiment becomes much faster, while its quality generally remains nearly identical to that obtained using a standard gas proportional counter. ... 

Circuits (1) and (2) may be used with ordinary diffractometers to increase the peak/background ratio of diffraction lines. They are by no means necessary quite adequate diffraction patterns can be obtained from a wide variety of specimens with no other discriminator than a Kp filter. Circuit (3) is required only in x-ray spectroscopy (Chap. 15), in a very special kind of diffractometry (Sec. 7-10), and with a position-sensitive proportional counter. Any one of these circuits is more effective, the better the resolution of the counter with which it operates. 

This is a very recent development. It involves a side-window position-sensitive proportional counter (Sec. 7-5), a multichannel analyzer, and the rpeasurement of the angular positions of many diffraction lines simultaneously. The anode wire of the counter, which is long and curved, coincides with a segment of the diffractometer circle and is connected, through appropriate circuits, to an MCA. The powder specimen is in the form of a thin rod centered on the diffractometer axis. The geometry of the apparatus therefore resembles that of a Debye-Scherrer camera (Fig. 6-2), except that the curved film strip is replaced by a curved counter. 

A more recent, and very promising, development is due to Cohen and James, who adapted a position-sensitive proportional counter to stress measurement. This counter has the great advantage that it can measure the 29 position of a diffracted beam without a 29 movement of the counter (Sec. 7-5). Preliminary work was done with the counter mounted on a standard diffractometer [16.10]. Later a portable instrument was made, in which the counter and a miniature, air-... 

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. 

WOL 83] WOLFEL E.R., A novel curved position sensitive proportional counter for x-ray diffractometry ,/. Appl. Cryst, vol. 16, p. 341-348, 1983. 

Fleischmann and co-workers have carried out a number of in-situ x-ray diffraction studies at roughened electrodes.Their experiments are different from those previously discussed in that instead of a synchrotron source they employ a conventional x-ray tube ( 1.5 kW) with a position-sensitive proportional counter for the measurement of the diffracted intensity. They have carried out experiments in both transmission (Laue) and reflection (Bragg) modes. 

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. 

The first TRXRD study of phase transitions occurring in membranes and membrane lipid extracts was described in 1972 [45]. It is interesting to note that these time-resolved measurements were realized through a technological innovation in the form of a linear, position-sensitive proportional X-ray counter. In the past decade, considerable interest in lipid phase transition kinetics has developed in response to the emergence of new technologies, the most important of which include the synchrotron radiation source, and X-ray optics and detectors. The increased interest level is reflected in a growing literature. 

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... 

Electronic counters are devices in which absorption of an x-ray photon or a neutron generates a short electric pulse in the associated electronic circuitry. By counting the rate of generation of such pulses, the flux of the x-ray or neutron beam to which the device is exposed can be measured. These counters are the outgrowth of the initial efforts made by nuclear physicists for detection of radioactivities of materials. Most useful among them for x-ray and neutron scattering studies are the proportional and scintillation counters described in Section 2.4.1. Further elaboration on these counters led to the development of position-sensitive detectors, explained in Section 2.4.2. Very recently, a number of novel devices based on new technologies have become available, and these are briefly introduced in Section 2.4.4. 

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 2.16 Schematic illustration of a one-dimensional position-sensitive detector. The gas-filled detector operates as a proportional counter, and the position information is encoded in the difference in the rise time between the pulses coming out of the two ends of the anode wire.

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

Single-wire position-sensitive proportional counters operating by charge division (as described in Sec., 13.10.1) have also been used. ... 

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