Analog detectors

The first laser Raman spectra were inherently time-resolved (although no dynamical processes were actually studied) by virtue of the pulsed excitation source (ruby laser) and the simultaneous detection of all Raman frequencies by photographic spectroscopy. The advent of the scanning double monochromator, while a great advance for c.w. spectroscopy, spelled the temporary end of time resolution in Raman spectroscopy. The time-resolved techniques began to be revitalized in 1968 when Bridoux and Delhaye (16) adapted television detectors (analogous to, but faster, more convenient, and more sensitive than, photographic film) to Raman spectroscopy. The advent of the resonance Raman effect provided the sensitivity required to detect the Raman spectra of intrinsically dilute, short-lived chemical species. The development of time-resolved resonance Raman (TR ) techniques (17) in our laboratories and by others (18) has led to the routine TR observation of nanosecond-lived transients (19) and isolated observations of picosecond-timescale events by TR (20-22). A specific example of a TR study will be discussed in a later section. 

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]. 

A method based on a similar principle was proposed for the determination of selenium in tellurium [155], A metal sample was dissolved in dilute (1 1) aqua regia to which an acidified solution of 4-phenyl-o-phenylenediamine was added. The resulting 5-nitro-piazelenol was determined chromatographicaUy on a column of SE-30 at 200°C with detection of the organic derivative of selenium by an electron-capture detector. Analogous methods were used for the analysis of selenium and mercury in pure sulphuric acid [156] and sea water [157]. 

Refractive-index detectors have the. significant advantage of responding to nearly all. solutes. That is, they are general detectors analogous to flame or thermal conductivity detectors in gas chromatography. In... 

The modern Russian MIA flaw detectors use pulse version of the method [1-3], which peirnits to produce very portable (0.7 - 1.5 kg) and simple instruments, convenient especially for in-service testing. The objects to be tested are multilayer structures of reinforced plastics, metals and other materials honeycomb panels, antenna fairings, propellers, helicopter rotors and so on. In mentioned instruments amplitude-frequency analog signal processing is used. 

The two effects just described help to determine the x-ray distribution at the target. Before an x-ray beam strikes a sample to be analyzed, the beam is usually modified further. For example, there may be absorption (and filtering) by the window of the x-ray tube, by an air path between tube and sample, by the walls of a cell containing the sample, and finally by the sample itself. Analogous considerations govern the absorption (and, with polychromatic beams, the filtering) of the beam entering the detector from the sample. 

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