Proportional counter detector

Multiwire position readout systems have been used for a number of years with proportional counter detectors (67, 68). Adaptations of this method have proved very successful in imaging applications with MCP s (1, 69-71). A typical arrangement (Figure 10) is described by Knapp (69) and consists of two planes of closely spaced wires. Each wire is 0.1 mm in diameter and individual wires are spaced at 0.2 mm intervals with a gap on the order of the wire spacing between the two planes. The wires in the two planes run orthogonal to each other to permit determination of both the x and y coordinates of an event. Resistors interconnect the wires in each plane and preamplifiers are connected to every eighth wire. Thus, a readout system of 130 + 130 wires, for example, requires 16 + 16 amplifiers. Electron clouds emerging from... 

Constant acceleration spectra were obtained with an Austin Science Associates, Inc. S-600 Mossbauer spectrometer equipped with an electromagnetic Doppler velocity motor. The source was 50 m Ci of Co diffused into a palladium matrix, and it was obtained from New England Nuclear, Inc. The pulses from the proportional counter detector (Reuter Stokes) were amplified, shaped and gated using Austin Science Associates electronics. These shaped pulses were then sent to a Tracor Northern NS-900 multichannel analyzer. The MCA was interfaced directly to a PDP-11 minicomputer, greatly facilitating data storage and analysis. 

The procedures for bombardment and analysis that we discuss below are described in greater detail in (I). After both the proton and He bombardments, samples were counted in calibrated Nal well detectors to establish absolute source intensity and time-decay characteristics. Sources were simultaneously analyzed by HPLC (with a Nal coincidence detector) and by GC (with a proportional counter detector) to determine their chemical composition. After chemical purification, the sources were again analyzed to determine purity. All absolute activities discussed below are normalized to a zero time at the end of the bombardment. 

Test methods that might be used for sulfur determination applications in fuels include techniques such as lead acetate paper tape, oxidative combustion followed by gas chromatographic separation for flame photometric detection [4], and energy dispersive X-ray fluorescence with coaxial proportional counter detectors [5]. The first of these two methods was recently issued as a new standard D 7041 by ASTM. However, these and other corrunercially available analyzers, such conventional on-line/at process sulfur by combustion and UVF analyzers typically require analytical cycle times of 4—10 min. This delay in reporting the sulfur concentration levels limits the real time detection capability of changes in the sulfur concentration of fast moving or rapidly changing transport or process streams. 

The X-ray analysis system for the EMA is a wavelength dispersive spectrometer with gas proportional counter detectors. In the SEM, an energy dispersive X-ray spectrometer with a Si(Li) detector is used. The entire electron and X-ray optical systems are operated under a vacuum of about 10 torr. Modem systems are completely automated with computer control of the instmment parameters, specimen stage movement, data collection and data processing. 

The other type of X-ray analysis system used with SEMs today is the wavelength spectrometer, illustrated in Fig. 5. Here the selective diffraction properties of a crystal in conjunction with a proportional counter detector is used to sort out the radiation according to wavelength. With suitable crystals, this system allows the analysis of all elements from Be-U. In addition to allowing the detection of light element radiation, the WDX spectrometer provides superior elemental discrimination compared to an EDX system. 

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. 

The slit distance of the proportional counter detector was 100 pm. The measuring of control data and the processing of measurement data were carried out by computer in both techniques. 

There are many types of electronic detector. The original fomi of electronic detector was the Geiger counter, but it was replaced many years ago by the proportional counter, which allows selection of radiation of a particular type or energy. Proportional counters for x-rays are filled witii a gas such as xenon, and those for... 

Alpha counting is done with an internal proportional counter or a scintiUation counter. Beta counting is carried out with an internal or external proportional gas-flow chamber or an end-window Geiger-MueUer tube. The operating principles and descriptions of various counting instmments are available, as are techniques for determining various radioelements in aqueous solution (20,44). A laboratory manual of radiochemical procedures has been compiled for analysis of specific radionucHdes in drinking water (45). Detector efficiency should be deterrnined with commercially available sources of known activity. 

Benchtop X-ray energy dispersive analyzer BRA-17-02 based on a gas-filled electroluminescent detector with an x-ray tube excitation and range of the elements to be determined from K (Z=19) to U (Z=92) an electroluminescent detector ensures two times better resolution compared with traditional proportional counters and possesses 20 times greater x-ray efficiency compared with semiconductor detectors. The device is used usually for grits concentration determination when analysing of aviation oils (certified analysis procedures are available) and in mining industry. 

At present, the Geiger counter is the most popular x-ray detector in analytical chemistry. Although it is yielding ground to the proportional counter and the scintillation counter, it will be remembered for having greatly accelerated the use of x-ray emission spectrography in analytical chemistry. 

In the phosphor-photoelectric detector used as just described, the x-ray quanta strike the phosphor at a rate so great that the quanta of visible light are never resolved they are integrated into a beam of visible light the intensity of which is measured by the multiplier phototube. In the scintillation counters usual in analytical chemistry, on the other hand, individual x-ray quanta can be absorbed by a single crystal highly transparent to light (for example, an alkali halide crystal with thallium as activator), and the resultant visible scintillations can produce an output pulse of electrons from the multiplier phototube. The pulses can be counted as were the pulses-from the proportional counter. 

Recent papers from the Philips Laboratories37 40 contain thorough discussions of the Geiger counter, the proportional counter, and the scintillation counter, and significant performance data for all three, the emphasis being placed throughout upon x-ray applications. The detection system employed by Parrish and Kohler was particularly noteworthy in that it could conveniently accommodate any one of four detectors. ... 

The tubes run cool when operated at capacity. No contaminant gives a line at intensity exceeding 2% of the strongest characteristic line from the target. (2) For reasons given in Chapter 2, the preferred detectors are scintillation and gas-flow proportional counters. (3) The com-... 

Gas-flow proportional counter, 55 in aluminum analysis, 217 in comparison with other detectors, 65-67... 

The basic function of the spectrometer is to separate the polychromatic beam of radiation coming from the specimen in order that the intensities of each individual characteristic line can be measured. In principle, the wide variety of instruments (WDXRF and EDXRF types) differ only in the type of source used for excitation, the number of elements which they are able to measure at one time and the speed of data collection. Detectors commonly employed in X-ray spectrometers are usually either a gas-flow proportional counter for heavier elements/soft X-rays (useful range E < 6keV 1.5-50 A), a scintillation counter for lighter elements/hard X-rays (E > 6keV 0.2-2 A) or a solid-state detector (0.5-8 A). 

The spectrometer is set to the appropriate Bragg angle 0 of the requisite characteristic wavelength, and only these X-rays will reach the detector and be counted. The detector employed is the gas proportional counter, which can operate at much faster count rates than the EDS crystal detector. 

OD Detectors are the classical proportional counters that are used in laboratory goniometers for decades. Because every point of reciprocal space is measured with the same cell, the detector response is uniform by definition. 

Gas-filled detectors are used, for the most part, to measure alpha and beta particles, neutrons, and gamma rays. The detectors operate in the ionization, proportional, and G-M regions with an arrangement most sensitive to the type of radiation being measured. Neutron detectors utilize ionization chambers or proportional counters of appropriate design. Compensated ion chambers, BF3 counters, fission counters, and proton recoil counters are examples of neutron detectors. 

A proportional counter is a detector that operates in the proportional region. 

A proportional counter is a detector which operates in the proportional region, as shown in Figure 6. Figure 7 illustrates a simplified proportional counter circuit. 

To a limited degree, the fill-gas will determine what type of radiation the proportional counter will be able to detect. Argon and helium are the most frequently used fill gases and allow for the detection of alpha, beta, and gamma radiation. When detection of neutrons is necessary, the detectors are usually filled with boron-triflouride gas. 

When radiation enters a proportional counter, the detector gas, at the point of incident radiation, becomes ionized. 

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