Detectors high resolution intrinsic

The availability of high flux thermal neutron irradiation facilities and high resolution intrinsic Ge and lithium drifted germanium (Ge(Li)) or silicon (Si(Li)) detectors has made neutron activation a very attractive tool for determining trace elemental composition of petroleum and petroleum products. This analytical technique is generally referred to as instrumental neutron activation analysis (INAA) to distinguish it from neutron activation followed by radiochemical separations. INAA can be used as a multi-elemental method with high sensitivity for many trace elements (Table 3.IV), and it has been applied to various petroleum materials in recent years (45-55). In some instances as many as 30 trace elements have been identified and measured in crude oils by this technique (56, 57). 

Occasionally, high resolution X-ray detectors made of very pure silicon can be found on the market. It seems, however, that the purification process of silicon does not yield the same excellent results as in the case of germanium. It is more of a lucky chance that sometimes the metallurgists succeed in producing a batch of silicon with an extremely low amount of impurities. Then, intrinsic silicon detectors are produced. 

Both dispersive (D) and Fourier transform (FT) micro-Raman are commercially available [507-509]. The choice between D- and FT-Raman has been discussed cfr. Chp. 1.2.3). However, as the intrinsic superiority of interferometers in terms of high resolution and geometrical extent cannot be exploited in micro-Raman spectroscopy, dispersive spectral analysers are preferred in combination with the microscope. FT-Raman instruments equipped with a microscope have thus far been limited to a sensitivity far lower than that of modern Raman microspectrometers equipped with multichannel detectors, which employ visible excitation. Consequently, FT-Raman microscopes often yield deceiving results with poor sensitivity and spatial resolution (from 15... 

In addition to the surface/interface selectivity, IR-Visible SFG spectroscopy provides a number of attractive features since it is a coherent process (i) Detection efficiency is very high because the angle of emission of SFG light is strictly determined by the momentum conservation of the two incident beams, together with the fact that SFG can be detected by a photomultiplier (PMT) or CCD, which are the most efficient light detectors, because the SFG beam is in the visible region, (ii) The polarization feature that NLO intrinsically provides enables us to obtain information about a conformational and lateral order of adsorbed molecules on a flat surface, which cannot be obtained by traditional vibrational spectroscopy [29-32]. (iii) A pump and SFG probe measurement can be used for an ultra-fast dynamics study with a time-resolution determined by the incident laser pulses [33-37]. (iv) As a photon-in/photon-out method, SFG is applicable to essentially any system as long as one side of the interface is optically transparent. 

Because of the underlying photophysics, fluorescence lifetimes are intrinsically short, usually on the order of a few nanoseconds. Detection systems with a high timing resolution are thus required to resolve and quantify the fluorescence decays. Developments in electronics and detector technology have resulted in sophisticated and easy to use equipment with a high time resolution. Fluorescence lifetime spectroscopy has become a popular tool in the past decades, and reliable commercial instrumentation is readily available. 

Even assuming that these limitations are acceptable, the most appropriate and promising techniques for security applications are based on nanosecond neutron analysis (not only in API) therefore, the use of HPGe with its intrinsically slow signal (timing resolutions of tens of nanoseconds at best) and low-rate capability is highly undesirable. The use of HPGe in this application with 14-MeV neutron sources has been described in the literature for more than 15 years with little evidence that such detectors improve real-world system performance and much evidence that they do not. 

A great advantage for CdTe and Hgl2 detectors, " compared to Ge and Si(Li) detectors, is that they can operate at room temperature (see also Sec. 7.5.6). At this time, they can be obtained in relatively small volumes, but they still have an intrinsic efficiency of about 75 percent at 100 keV because of the high atomic number of the elements involved. The energy resolution of CdTe detectors is 18 percent at 6 keV and 1.3 percent at 662 keV. The corresponding numbers for Hgl2 are 8 percent and 0.7 percent. ... 

For truly multielement determinations, increased selectivity is required. It is offered by semiconductor detectors, e.g., by lithium-drifted germanium [Ge(Li)] or intrinsic germanium (high-purity) [HP-Ge] types with a resolution - full width at half maximum or FWHM... 

Two type of detectors are used in commercially available units proportional detectors and semiconductor detectors such as silicon PIN, Si(Li), Ge(Li), and silicon drift detectors. The detectors used in EDXRF have very high intrinsic energy resolution. In these systems, the detector resolves the spectrum. The signal pulses are collected, integrated, and displayed by a multichannel analyzer (MCA). 

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