Vidicon devices

Milano et al. [153, 154] and Cook [34] introduced an approach to derivative spectra by substituting electronic wavelength modulation for the mechanical systems used in derivative spectrometers. This effect is achieved by superimposing a low-amplitude, periodic wave form on the horizontal sweep signal. In this way spectra were generated. Warner et al. [155] applied a vidicon detector for fast detection of fluorescence spectra and obtained derivatives of the stored data by digital computation. Cook et al. [156] also made use of a silicon vidicon detector for multichannel operations in rapid UV-VIS spectrophotometers with the possibility of first-order differentiation. For the same purpose Milano et al. [93, 157] used a multichannel linear photodiode array for detection of spectra in polychromator optics and stored data manipulations (d ). Technical explanations of the principles of diode array and vidicon devices cem be found in [158-161]. 

Application of experimental devices allows to perform NDT of products, made out of materials of low density (Al-Mg - alloys, Be, plastics) with high defectoscopic sensitivity up to 0,5 %. Inch-size X-ray vidicons used complete with microfocal X-ray tubes and X-ray image enlargement method allow to obtain resolution up to SO pairs of lines per mm. 

The main detectors used in AES today are photomultiplier tubes (PMTs), photodiode arrays (PDAs), charge-coupled devices (CCDs), and vidicons, image dissectors, and charge-injection detectors (CIDs). An innovative CCD detector for AES has been described [147]. New developments are the array detector AES. With modem multichannel echelle spectral analysers it is possible to analyse any luminous event (flash, spark, laser-induced plasma, discharge) instantly. Considering the complexity of emission spectra, the importance of spectral resolution cannot be overemphasised. Table 8.25 shows some typical spectral emission lines of some common elements. Atomic plasma emission sources can act as chromatographic detectors, e.g. GC-AED (see Chapter 4). 

In contrast to the image dissector, which measures the photon flux, the vidicon is an integrating device, where the target serves as a memory buffer, storing information until the scanning electron beam reads and erases it. 

Switch-Board Optics. The preceding discussion has summarized the various approaches which have been taken to achieve a practical spectrometer for SMA. The direct reader, the vidicon detector, and the development of image device/echelle systems... 

The results obtained with this first generation focal plane M.S.-EOID system as well as studies by Beynon and others at Purdue University (15) demonstrated the technical feasibility of such a system. Furthermore, these studies led the way to solutions for the variety of fundamental problems, which were encountered during the development and helped point out the directions towards future changes necessary on the road towards a commercially practical design for use of the concept in routine applications of mass-spectrometry. It became obvious that the vidicon based camera system wets not the best approach. Some of the reasons for this are (1) Loss of sensitivity due to light losses in the dissector and the transfer optics (2) cost of the image dissector (3) lower dynamic range and sensitivity, slower read-out rate, etc., of the vidicon compared to alternate devices. 

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. 

The first detectors to be used in OMA systems were standard TV image tubes. These were silicon vidicons or the more sensitive Silicon Intensified Target (SIT) detectors, which both employed silicon targets to convert optical information into electronic form. More recently, the use of solid state detectors in the form of a diode array (Reticon) has been found to have some advantages over the vidicons and SIT tubes. Current developments in the field of charge coupled devices (CCD) will probably soon provide an even better multielement detector for use in OMA systems. 

The first attempt to realize such imaging device uses was made by Imamura et al. (1979), and a vidicon-type image pickup tube was proposed. Especially in the field of color television cameras, there have been great expectations that this device will lead to the realization of high-performance imagers. 

In the area-image sensor, it is expected that highly sensitive solid-state image sensors with high resolution, competitive with vidicons, will become available. The solid-state image sensor, which is made of an a-Si H photodiode array on a Si IC scanner, is the most suitable device for this purpose. 

Other reports deal with individual elements, such as Ni [1, 86, 87] or Fe [11,84]. The efficiency [71—73] of flame methods (AAS) has been compared with flameless techniques (NFAAS) (Table 6). Because of their significance there have been attempts to determine the elements P [38] and S [78] directly with AAS. This, however, requires a device which can measure ultraviolet lines (ca. 180 nm) with sufficient sensitivity. Good results can also be achieved by gas chromatographic separation and successive AAS determination [92] and simultaneous multielement analysis with a Vidicon-detector has been tried [68] because the speed with which the information is gained can be very important in practice. Some work [39, 53] reports on the problem of molecular bands which can appear when working with... 

Photo-Electronic Imaging Devices 6.1 Vidicon-Tube Based Detectors ... 

Modern vidicon tubes with an integrated amplifying system exist in the form of the Silicon-Intensifier-Tanget-Tube (SIT-Tube). The main structure of this family of devices is shown in Fig. 17. It consists of an image-intensifier section, followed by a... 

Although vidicon-tubes are commercial devices, it still takes a long way to turn them into an excellent X-ray detector. For accurate amplitude measurements, quite some effort has to be invested in the development and tests of the different components. 

A new type of imaging devices has been introduced a decade ago These devices consist of an array of photo-sensitive diodes, coupled to a CCD read-out system. CCD s are based upon the transfer of charge packets in a repetitive metal-oxid°-silicon (MOS) structure (see Fig. 20). The charges in the elements of a CCD can be photo-generated, e.g. by the absorption of X-rays in the substrate, and then shifted out electronically to a single output. In a way CCD s operate as the solid state selfscanning equivalent of a vidicon-tube. 

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