Scattering length density Neutron

Neutron scattering is also useful for the study of adsorbed material on hydrosol particles. The neutron scattering length densities of hydrogen and deuterium differ considerably. By preparing a hydrosol in an appropriate H20/D20 mixture, it is possible to match the neutron scattering length densities of the dispersion medium and the core particles. The neutron beam thus sees only the adsorbed layer, the thickness of which can be estimated. Alternatively, the dispersion medium can be matched to the adsorbed layer to permit estimation of the core-particle size. 

Pore masking is not always easy in an X-ray s.a.s. experiment because certain supports have such high electron densities that it is impossible to find a fluid which can match them.47 It is here that neutron s.a.s. can be particularly useful since it is relatively easy to find a suitable fluid with the same neutron scattering length density as a chosen catalyst support. 

Table 4a Neutron scattering-length densities (n.s.l.d.) of some supports and maskants...

In the simplest case of the interface between two bulk media, the reflectivity is related to the refractive index difference across the interface, and is described by Fresnel s Law [18]. The refractive index, n, is related to the neutron scattering length density, such that... 

X-ray and neutron specular reflection Molecular structure across the interface, laterally averaged over the beam area X-rays electron density profiles neutrons scattering length density profiles of the nuclei of atoms). With neutrons different parts of the monolayer can be studied independently by selective H/D substitution. See ellipsometry. 

C is a constant, and < > denotes an equilibrium average. For small-angle neutron scattering (SANS), the scattering factor is proportional to the coherent neutron scattering-length density 6, giving the result that... 

Neutron Scattering Length Densities of Several Common Polymers and Solvents... 

Here the term (pp — pnl)2 replaces the refractive index term in equation (7.3) pp and pm are, respectively, the neutron scattering-length densities of the particle and the medium. A is a constant incorporating the other factors in equation (7.3) and is a characteristic of the apparatus, i.e. the. wavelength of the neutrons, the distance from target to detector. In this case the simple equation for P(Q) given in equation (7.13) no longer applies. For spheres it now has the form... 

The first arises from the fact that the neutron scattering-length densities of different atoms vary widely in particular those for hydrogen and deuterium differ considerably so that by mixing H2O and D20 in varying proportions media of widely different values of p can be prepared. Equation (7.18) shows that if Pp = Pm there is no scattering, i.e. neutrons do not see the particles. This principle can be exploited in the study of compo-... 

The scattering of a molecular material is characterized by the neutron scattering length density, 2, defined by... 

Species Density, p(gm cm ) X-Ray scattering length density, Px(10 °cm ) Neutron scattering length density, pn(10 °cm" )... 

For SAXS, the neutron scattering length density p ) is replaced by the product of the electron density (pe) and the Thompson scattering length (/j = 0.282 x 10 cm), and vice-versa. 

The first analysis performed for the Lio,6FeP04 solid-solution phase at 620 K was the Rietveld refinement for the neutron diffraction profile and the resultant pattern is summarized in Fig. 14.12b. To evaluate the dynamic disorder of lithium, maximum entropy method (MEM) was applied to estimate the neutron scattering length density distribution, which corresponds to the nuclear density distribution. 

Polymer or solvent Density",/o (gem (atr 23°C) Neutron-scattering-length density, p (10 cm )... 

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