Multi-channel analyser

A suspension of particles in an electrolyte is drawn through a small orifice on either side of which is positioned an electrode. A constant electrical current supply is connected to the electrodes and the electrolyte within the orifice constitutes the main resistive component of the circuit. As particles enter the orifice they displace an equivalent volume of electrolyte, thereby producing a change in the electrical resistance of the circuit, the magnitude of which is related to the displaced volume. The consequent voltage pulse across the electrodes is fed to a multi-channel analyser. The distribution of pulses arising from the passage of many thousands of particles is then processed to provide a particle (volume) size distribution. 

The spectrum is scanned repetitively and accumulated until the signaknoise ratio is adequate. Depending on the count-rate, i.e. the strength of the source, this may take a few minutes or several hours. Accumulation is normally in a multi-channel analyser, so that the spectrum is obtained in digitized form and may be transferred directly to a computer which fits a calculated spectrum to the data points modern spectrometers are effectively PCs with built-in data processing. The fitting programme takes estimates of the parameters supplied by the user, from which a trial spectrum is calculated, and an iterative process optimizes the parameters. 

The classical time measuring system, the combination of a Time-to-Amplitude Converter (TAG) and a Multi-Channel-Analyser (MCA) has a much longer deadtime of the order of 20 psec. 

The instrumentation used to measure y-rays is generally a semiconductor detector (Nal(Tl) crystal) associated to a multi-channel analyser to cover energies over the range from about 60 keV to 3.0 MeV. The functioning is similar to that of liquid scintillators. 

Most spectrophotometric flow-based analytical procedures involve single analyte determination or multi-parametric determinations carried out in multi-channel analysers, with an independent analytical channel for each analyte. Consequently, analytical results are obtained after converting all of the recorded peaks to single values [139], usually referred to as the analytical signals. 

The incorporation of computers into clinical chemistry has run in parallel with the automation and commercialization of complex analysers. The operation of multi-channel analysers is controlled by suitable software, as is the acquisition of analytical data. The earliest clinical analysers including computerized control of the analytical process were marketed in 1970. Virtually every analyser launched after 1980 is microprocessor-controlled. 

Neglecting the photo-degradation processes in laser dyes the partial photochemical quantum yields of stilbene-1 derivatives have been determined by evaluation procedures as given above [93]. In Section 4.3.2 a microprocessor controlled device is described [176], which allows convenient measurement of the data. Even an optical multi-channel analyser can be used [175]. 

The energy spectra discussed below were obtained with a Packard Tricarb Spectrometer 3380, in combination with a Packard multi-channel analyser Spektrazoon 930. The spectra displayed on the screen of the multi-channel analyzer were photographed with a reflex Ccunera. 

VG Isotopes Ltd., is another leading manufacturer of ICP-MS equipment. The special features of their VG Plasmaquad PQ2 includes a multi-channel analyser which ensures rapid data acquisition over the whole mass range. The multi-channel analyser facilities include 4096 channels, 300 m facility for spectral analysis, user-definable number of measurements per peak in peak jumping mode, and the ability to monitor data as they are acquired. A multi-channel analyser is imperative for acquiring short-lived signals from accessories such as flow injection, electrothermal vaporisation, laser ablation, and so on, or for fast multi-element survey scans (typically 1 minute). 

In some countries, the radioactivity limits for releasing the stones have become nuclide specific. This will require the use of a multi-channel analyser as well as a system for determining the beta emissions from the stones. 

The fluorescence radiation is usually recorded with a Si(Li) detector and is registered by a multi-channel analyser as is the norm in energy-dispersive spectrometry. The detector is mounted directly above the sample, perpendicular to the sample support, at a distance of less than 1 mm in order to enlarge the angle of reception and to maximise the fluorescence intensity. Si(Li) detectors with active areas of 30 and SOnun and spectral resolutions of about 135 and 150 e V at 5.9 keV, respectively, are in common use. Normally measurements are performed in ambient air. 

X-ray spectra from real samples are complex. Their evaluation requires deconvolution of overlapping peaks and automatic background subtraction. Commercially available spectrum processing software fulfills these demands and, moreover, facilitates the operating procedures by use of a multi-channel analyser. 

Fig. 5.17. Functional diagram of the electronic radon gas personal dosimeter DOSEman. MCA multi-channel analyser, EEPROM electrically erasable programmable read only memory, IrDA infrared inteface.

Tools for transient thermal-hydraulic and fuel performance analysis. Code development in progress DSNP, MATRA Multi-channel Analyser for steady state and Transients in Rod Arrays... 

X-ray intensity due to a particular element is proportional to the concentration of that element in the sample. There are two types of instrument in production those in which the emitted radiation is separated by wavelength using crystals as gratings, i.e., total reflection XRF (wavelength dispersive XRF WDXRF or total reflection XRF TRXRF) and those in which the radiation is not separated but identified by energy dispersive electronic techniques using solid-state detectors and multi-channel analysers, i.e., energy dispersive XRF (EDXRF). 

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