Scattering origin

Exposure Time Perform some test exposures and choose an exposure time so that the maximum scattering originating from the sample results in about 10,000 counts in some of the relevant pixels. Is the maximum lower than 2000 counts, a quantitative analysis will be very difficult. 

The introduction of the commercially available mass detector meant an expansion of the possible conditions for TG separations, including that of gradient elution. The mass detector showed very narrow and symmetrical peaks, which indicated its usefulness for this application. The goal was to find a system that could be used to separate any natural TG mixture regardless of its carbon number distribution. The basic principle of this detector, i.e., the light scattering, originally was presented by Charlesworth (104). 

Electronic Raman scattering originates not only from free electron excitations, but also from collective electron excitations in the form of plasmons. So far, these two types of excitation have been observed only in conventional semiconductors and to some extent in high temperature superconductors, as discussed in subsections 4.8.4 and 4.8.5. However, doped polymers with not too high carrier concentrations or charge transfer systems are possible candidates, and the search for electronic Raman scattering in such systems is one of the challenges in this held. 

Exposure Time Perform some test exposures and choose an exposure time so that the maximum scattering originating from the sample results in about... 

Macromolecules in solution as described by Eq. (10) give rise to three basic scattering functions. I, (h) is the off-resonance scattering, originates from the structure of the resonant scatterers alone, and I ,(h) is a cross term, containing the influence of both u(r) and v(r) as their convolution. In many cases the resonant scattering terms in Eq. (16) may be much smaller than I (h). The quadratic term in Eq. (16) can then be neglected and we obtain... 

A much mure troublesome problem occurs when Ihe source of absorption or scattering originates in Ihe sample matrix. In this instance, the power of the transmitted beam P is reduced by the matrix components, but the incident beam power Pq is not a positive error in absorbance and thus concentration results. An example of a potential matrix interference because of absorption occurs in the determination of barium in alkaline-earth mixtures. As shown by the solid line in Figure 8-8, the wavelength of Ihe barium line used for atomic absorption analysis appears in Ihe center of a broad absorption band for CaOH. We therefore anticipate that calcium will interfere in barium determinations, but the effect is easily eliminated by substituting nitrous oxide for air as Ihe oxidant. The higher temperature of the nitrous oxide flame decomposes the CaOH and eliminates Ihe absorption hand. 

Fig. 7. Miniature Raman cell for frozen protein solutions that, once loaded with sample, can conveniently be shipped between laboratories in dry ice or liquid Nj and then attached without further manipulation to a helium closed-cycle refrigerator (CCR) station for RR measurements. The main advantages of this design are as follows (1) very small quantities of sample are required (1-2 drops) (2) the cell atmosphere can be controlled (3) cryogenic temperatures are obtained, down to 10 K and (4) Raman scattering originates directly from the surface of a frozen solution without interferences from glass or quartz scattering. ...

For scattering by a single intermediate electronic state, we can replace the sum in Eq. (1) by a vibrational sum. We now consider specifically scattering from the level / > = Stokes scattering originating from the... 

Thus far we have only considered Stokes scattering, namely, scattering originating from molecules in their electronic and vibrational ground state. 

According to the factorization theorem the cross section for a hard scattering originating from an interaction of two hadrons with four-momenta Pi and P2 can be written as... 

Neutrons are scattered isotropically from individual nuclei, whereas, for LS and SAXS, the scattering originates in the electron cloud, so the atomic form factors are in principle (2-dependent. However, the variation is small in practice (<1% for Q < 0.1 A ) and is usually neglected for SAXS and LS [36]. The Thompson-scattering amplitude of a classical electron is rj = 0.282 x 10 cm [65], so the X-ray scattering length of an atom, /, is proportional to the atomic number (/ = rjZ) and increases with the number of electrons per atom. For neutrons, values of b vary from isotope to isotope (see below). If the nucleus has nonzero spin, it can interact with the neutron spin, and the total cross section (atot) splits into coherent and incoherent components as explained below. 

The scattered beam is, beyond trivial factors such as incoming flux, transmission and geometric factors, proportional to two terms (i) a contrast factor reflecting the ability of individual atoms to interact with the radiation and (ii) the structure factor resulting from interference effects of scattering originating from different sites in the sample, providing information on structural properties. 

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