Background light

As was mentioned in Section 12.1, there is a relationship between metal production and diffuse background radiation, perhaps more properly referred to as extragalac-tic background light (EBL), shown in Fig. 12.1, since most or all of it comes from individual galaxies. 

Advantages — Optical transparency and flatness low intrinsic fluorescent backgrounds light scattering ultraflatness impervious surface allows high density array construchon. 

Figure 11.13 shows a typical DO AS spectrum measured in air after correcting for atmospheric background light and an electronic offset (Stutz and Platt, 1997). Below the spectrum are shown reference spectra for the gases that contribute to the atmospheric spectrum, scaled by the a, factors determined using Eq. (H). In this case, O, N02, SOz, and HCHO all contribute, leaving a residual spectrum with a peak-to-peak absorbance of 6 X 10 4. 

For a black body at 300 K, = 9.8 /mi. A filter is included which cuts out radiation of wavelength shorter than about 5 /mi and so prevents the device from responding to changes in background lighting levels. Such a detector is capable of responding to a moving person up to distances of 100 m. 

Flame AFS combines features of both AAS and FES. The excitation of atoms is by the absorption of light. When individual element spectral line sources are used, the spectral selectivity should be as high as that in AAS, although scatter may be more of a problem in AFS. Quantification is by comparison of the intensity of fluorescence emitted by samples with that emitted by standards of known concentration. At low determinant concentrations, it is necessary to discriminate between small fluorescence emission signals and the background light levels associated with thermally excited emission from the flame. Therefore in AFS, as in FES, it is desirable to have low flame background emission. This is discussed further in Chapter 2, where instrumental aspects of flame spectrometric techniques are discussed. 

A 6-inch, f/3.8 objective lens with coated optics was used in conjunction with a 4V2-inch extension tube. Three No. 5 medium peak flash bulbs connected in series provided the proper background lighting. The Dynafax capping shutter is equipped with a synchromatic delay which provided synchronization for this type of lamp. 

Itoh, T., Biju, V., Ishikawa, M., Kikkawa, Y., Hashimoto, K., Ikehata, A., Ozaki, Y. (2006). Surface-enhanced resonance Raman scattering and background light emission coupled with plasmon of single Ag nanoaggregates, y. Chem. Phys. 124 134708-1-6. 

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