Detector types elemental

The detection performance of an LIF photometric device is governed by the emission filter(s), excitation filter(s), detector type, the excitation source and the detection scheme. The selection of optical elements and device configuration as it relates to the detection performance is further described by expanding the collection efficiency term in Equation 11.3 ... 

In an alternative embodiment, the detector elements are separated by n-type regions 16 and a gate 17. The detector gate 1 consists of detector gate elements connected to each other by connectors 15. When a detector element is exposed to a high intensity of radiation excess charge is drained off via the regions 16. 

Lithium drifted detectors are produced by first doping an intrinsic crystal (Ge or Si) with p-type impurities such as B, Al, Ga or In. Lithium, a strongly n-type element, is then drifted into one end of the crystal. On refrigeration of... 

Some additional selective detectors have been described, but their use in biochemical GC has been minimal thus far. Among them, most notably, belong various optical spectroscopic detectors as well as various element-specific detectors based on the solute combustion and measurement of electrolytic conductivity [128]. While little has happened during the last decade with further development of the latter detector types, various gas-phase optical devices remain among the most interesting detectors for future studies. Element-specific plasma devices [129], UV absorption... 

Correction for the detector dead time t can be accomplished fairly easily and automatically via the instrument s software once the correct value is known. For isotopic analysis, one should never rely on a value predefined by the instrument manufacturer, but should determine the actual value experimentally. This is preferably done using the target element itself, as at least for some detector types, it has been demonstrated that the experimentally determined dead time may vary as a function of the element s mass number [115], Dead time determination also has to be repeated regularly, as it changes upon aging of the detector. When during experimental dead time determination a very aberrant behavior is obtained (i.e., the results make no sense), this is often indicative of detector problems the detector can, for example, be at the end of its lifetime. 

Detector type One single MCT" detector 16 element array MCT" detector... 

Even if all possible measures to improve depth resolution are applied, there still exist the effects of the primary ion beam-induced damage experienced by the substrate as a result of the sputtering process. These are discussed in Section 5.3.2.4.1. Crater edge effects and crater base effects can also result in the loss of depth resolution. These are discussed in Sections 5.3.2.4.2 and 5.3.2.4.3, respectively. Dynamic range pertains to the range of concentrations of a specific element or molecule that can be examined in a particular depth profile. As can be envisaged, this depends on the detection limit and on the detector type or combinations thereof (detectors are covered in Section 4.2.3.3). 

Single-element infrared and visible detector systems are used in a wide variety of industrial, medical, military, and recreational applications. Each application has requirements that will sway the design engineer toward a type or types of detector, electronics interface scheme, and product packaging. We describe here briefly representative applications, and the detector types chosen for that application... 

The University developed a method of determination of the material residual strength, based on measurement of the change of phase velocity of ultrasonic waves, as well as an ultrasonic flaw detector-tomograph with multi-element transducers of the type of phased acoustic array. It enables control of the internal structure of materials and products of up to 300 mm thickness, with the resolution of up to 0.5 mm. In the same university, work on NDT is also carried out in the welding and electro-acoustic departments. 

The array detector (collector) consists of a number of ion-collection elements arranged in a line each element of the array is an electron multiplier. Another type of array detector, the time-to-digital converter, is discussed in Chapter 31. 

A multipoint ion collector (also called the detector) consists of a large number of miniature electron multiplier elements assembled, or constructed, side by side over a plane. A multipoint collector can be an array, which detects a dispersed beam of ions simultaneously over a range of m/z values and is frequently used with a sector-type mass spectrometer. Alternatively, a microchannel plate collector detects all ions of one m/z value. When combined with a TOP analyzer, the microchannel plate affords an almost instantaneous mass spectrum. Because of their construction and operation, microchannel plate detectors are cheaper to fit and maintain. Multipoint detectors are particularly useful for situations in which ionization occurs within a very short space of time, as with some ionization sources, or in which only trace quantities of any substance are available. For such fleeting availability of ions, only multipoint collectors can measure a whole spectrum or part of a spectrum satisfactorily in the short time available. 

Alternatively, the ions in a mass spectrometer can also arrive at a multipoint collector as a temporally dispersed beam. Therefore, at any point in time, all ions of the same m/z value arrive simultaneously, and different m/z values arrive at other times. Ail elements of this collector detect the arrival of ions of one m/z value at any one instant of time. This type of detector, which is also an array, is called a microchannel plate collector of ions. 

An alternative type of spectrometer is the energy dispersive spectrometer which dispenses with a crystal dispersion element. Instead, a type of detector is used which receives the undispersed X-ray fluorescence and outputs a series of pulses of different voltages that correspond to the different wavelengths (energies) that it has received. These energies are then separated with a multichannel analyser. 

Several types of secondary pyrometer are available. In addition to those that measure by varying lamp current, some pyrometers maintain the lamp at constant current but interpose a wedge of graduated neutral density, whose position is a measure of temperature. Also, automatic pyrometers are available in which the eye is replaced by a detector and the measuring element is operated by a servo. In general, the accuracy of the automatic pyrometer is somewhat less than that achieved manually by a skilled operator. 

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