Photomultiplier detector system

Film and Photomultiplier Detector Systems. In the original ultracentrifuge built by Svedberg and co-workers (3,4) and also in the commercial instrument, the light intensity pattern was recorded on film, requiring a densitometer to obtain the absorption profile. Schachman and co-workers ( 5,6) constructed a mechanically scanned photomultiplier system in the early 1960 s. In addition to a commercial version now available (7), a number of other systems with computer controlled gathering of data have been constructed (8, , 10, 11, 12). 

In general, we are satisfied with the performance of our OMA-based light detector system for the absorption optical system in the ultracentrifuge. Many of the problems that we had to solve were inherent in the optical system and the cells, but were hidden to users with photomultiplier detector systems. Other problems associated with the SIT vidicon have been satisfactorily solved. 

The ellipsometer used in this study is described elsewhere(3). It consists of a Xenon light source, a monochromator, a polarizer, a sample holder, a rotating analyzer and a photomultiplier detector (Figure 1). An electrochemical cell with two windows is mounted at the center. The windows, being 120° apart, provide a 60° angle of incidence for the ellipsometer. A copper substrate and a platinum electrode function as anode and cathode respectively. Both are connected to a DC power supply. The system is automated with a personal computer to collect all experimental data during the deposition. Data analysis is carried out by a Fortran program run on a personal computer. 

Relatively recently, AIS Sommer GmbH of Germany delivered a laser-induced fluorescence (LIP) analyzer for quality control in minerals and mineral processing (Broicher 2000). The LIP analyzer includes two light detector systems with three photomultipliers each, which evaluate three spectral bands in two time windows each. It was done in the Kiruna phosphorous iron ore mine, Sweden. The limitation of LIP analysis is that its accuracy depends on the complexity of the composition of the ore and the concentration and fluorescence properties of the critical minerals in relation to all the other minerals present. The phosphorous iron ore in Kiruna is ideal for LIP analyzes, because its iron minerals are practically non-luminescent, while magmatic apatite is strongly fluorescent with intensive emissions of Ce and Eu ". ... 

Stroboscopic method. In this method the photomultiplier is also gated or pulsed having an on-time of nanosecond or subnanosecond duration during which it operates at very high gain. The flash lamp and the detector systems are synchronized such that a suitable delay can be introduced between the two. The gated photomultiplier samples the photocurrent each time the lamp fires and the photocurrent is thus proportional to the... 

Figure 3. Schematic of turbulent combustor geometry and optical data acquisition system for vibrational Raman-scattering temperature measurements using SAS intensity ratios. Also shown are sketches of the expected Raman contours viewed by each of the photomultiplier detectors, the temperature calibration curve, and several expected pdf s of temperature at different flame radial positions. The actual SAS temperature calibration curve was calculated theoretically to within a constant factor. This constant, which accounted for the optical and electronic system sensitivities, was determined experimentally by means of SAS measurements made on a premixed laminar flame of known temperature. Measurements of Ne concentration were made also with this apparatus, based on the integrated Stokes vibrational Q-branch intensities. These signals were related to gas densities by calibration against ambient air signals.

The multielement detection limits with the echelle/image dissector are comparable to, or better than, single element detection limits reported for a silicon vidicon and conventional optics. Detection limits for Cr, Cu, and Mn with the echelle/ image dissector compare favorably with single element data reported for a conventional atomic absorption instrument with a photomultiplier detector, but detection limits obtained here for Ni and Co are higher by factors of 10 or more than for the conventional instrument. The echelle/image dissector system should be adaptable to a so-called flameless atomizer and be subject to the same improvements in sensitivities and detection limits as conventional detector systems. 

Data presented in Table XI provide a comparison of results obtained with the present instrument with results reported by others with other systems. Results in the second column represent detection limits observed in this work. Results in the third and fourth columns represent detection limits reported for single element determinations with conventional optics and photomultiplier detectors. The results in the third column were obtained with similar dc plasmas (27, 34, 35, 36) and the results... 

Vidicon Detector Systems. It was obvious to many workers that the use of a television camera tube as the light detector would offer a number of advantages over the photomultiplier tube. The viewing of the image in real time would aid in aligning the optical system and also in decision making during an experiment. 

When the commercial OMA (Model 1205, Princeton Applied Research Corporation, Princeton, NJ) became available, we recognized its potential as a replacement for the photomultiplier detector. The vidicon detector surface was divided into 500 channels, the image could be seen on a cathode ray tube (CRT) monitor in real time, the intensity profile was available in digital form, the profile could be time-averaged for any desired number of video scans, and the final profile was stored in internal memory for transfer to an external output device. Not only had a considerable amount of work gone into its development and the verification of performance, but its potential for use for a variety of physical techniques would ensure the construction of enough units to support further development of the system. Moreover the need for low-light-level detectors for other purposes would lead to further improvements in detector devices. 

Emission interference was common in many early instruments which were accessories for UV/visible spectrophotometers, which operated in most instances on a d.c. system. The interference was caused by emission of the element at the same wavelength as that at which absorption was occurring. All modem instruments use a.c. systems which are of course blind to the continuous emission from the flame. However, if the intensity of the emission is high, the noise associated with the determination will increase, since the noise of a photomultiplier detector varies with the square root of the radiation falling upon it. 

With a photomultiplier detector, the measurement can be done simply by observing the signal maximum with an oscilloscope as the wavelength is scanned by hand or electronically. Alternatively a pulse integration system can be employed to record the spectra. The use of a CCD detector for such measurements is advantageous since the detector itself serves to integrate the pulsed signal. Such measurements are described in Ref. 9. 

Because the data manipulation and interpretation schemes were rather simplistic in their approach, not fully realizing the potential advantages of the "parallel" nature of the SPD these results cannot be considered optimal. However, these results are adequately characteristic of the overall performance of the SPD detection system and are therefore indicative of both its deficiencies and advantages over single channel photomultiplier detectors and could therefore, suggest some future modifications... 

In situ transformations in organic samples can be observed in real time in the DAC by using a microscope equipped with a CCD video monitoring system and luminescence spectrometer. A high-pressure mercury lamp is used to excite fluorescence in the sample. The emitted light from the sample is split with one part used for visual observation and the other part for analysis made possible by use of a grating spectrometer and a photomultiplier detector [22]. 

The limited availability of affordable commercial RSSF instruments has been an important factor that has prevented the widespread application of RSSF spectroscopy to the study of biological systems. However, in the past year, a significant change in the availability of commercial instrumentation hats come about. There currently are at least five manufacturers of computerized rapid-scanning detector systems. The choices in commercial instrumentation range from a mechanically scanned system with a single photomultiplier detector to photodiode array detector systems. This review includes descriptions of the currently available commercial systems. Because the authors experience in the field of RSSF spectroscopy is limited to the use of diode array detector systems and because most of the commercial instruments have appeared on the market just within the past 12 months, it has not been possible to make detailed performance evaluations and comparisons of the new commercial systems. 

Minimal emission. In an a.c. system, emission from the burner will not produce a photometric error. However, high emission will contribute to the flicker of the output, because the noise current from the photomultiplier detector increases as a function of the total light faUing on it. A very bright flame will therefore tend to produce a fluctuating output. 

If the resonance detector is well-designed, the vast majority of the magnesium atoms are unexcited. The resonance lines from the magnesium hollow cathode lamp will cause the magnesium atoms in the resonance detector to fluoresce. Some of this fluorescence will fall on a photomultiplier detector placed at right angles to the optical path. The intensity of fluorescence is proportional to the intensity of emission. Non-resonant lines from the lamp or from the flame will have no effect on the resonance detector. Therefore, a system of narrow bandwidth is produced without the requirement of a monochromator. 

The Phoswich Detector System (PDS) consists of a square array of four independent NaI(Tl)/CsI(Na) phoswich scintillation detectors. Each of the four detectors is made of two crystals of Nal(Tl) and CsI(Na) optically coupled and forming what is known as PHOSWICH (acronym of PHOsphor and semdWICH). The scintillation light produced in each phoswich is viewed, through a light guide of quartz, by a photomultiplier tube (PMT). The Nal(Tl) acts as X-ray detector, while the CsI(Na) scintillator acts as an active shield. 

Cross-talk is the interception of unwanted light in the region of the slit and photomultiplier tube (PMT). This occurs when the radiation from a strong emitter falls upon the slits, mirrors, and detectors of adjacent analytes. For example, if the detector system for the Cr 267.716nm line is located next to the very intense Mg 279.553 nm line in the focal plane, cross-talk can occur if detection optics have not been adequately masked. 

Although there are still a few commercially available instruments for phosphorescence measurements based on mechanically chopped systems, nowadays most of the commercial luminometers used for phosphorescence measurements are based on pulsed-source/gated detections. These pulsed instruments are typically equipped with a high-power xenon flash-lamp and a photomultiplier detector. 

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