Neutron scattering densities

The constant depends on the radiation used, as does (dp Jdc ), which is the refractive index increment for light, the electron density increment for X-rays, and the neutron scattering density increment for neutrons. 

Because mass density increments could not be determined for potassium phosphate solutions, a value of v2 = 0.75 was assumed in order to interpret the neutron scattering density increment. 

FIGURE 9.2 Neutron-scattering-density profiles p(z) for a lithium-substituted vermiculite. Oxygen plus clay layer is the solid line, hydrogen is the dashed line, and lithium is the stars. The molecular model above shows two sections of clay surface and an undistorted octahedral Li+(H20)6 complex. In this model all six water molecules are hydrogen bonded directly to the clay plate in practice we find that, on average, two of the six water molecules are less strongly oriented toward the plate. 

Fig. 6. "Difierence neutron-scattering density corresponding to Fig. 5. (From a photograph kindly supplied by Prof. G. E. Bacon. Negative density own by broken contours)...

Fig. 2. Schematic variation of neutron scattering density for an object composed of a central sphere of RNA and a concentric outer shell of protein, i.e. a simple virus. The contrast difference dp is the difference between the scattering density of the solvent pg and the solute py. High positive and negative dp are seen in 0 and 100% H20. The protein shell is matched-out in 43% H20 and the RNA core is matched-out in 72% H20. Note that for reason of solvent H- H exchange, the average protein and RNA densities increase slightly on going from 0 to 100% H20. Solution scattering is observed where the solute and solvent densities are different. Note that the fluctuations in scattering densities pp(r) within each of the protein and RNA components do not disappear at their respective matchpoints. See Section 2.3 for a further explanation of the terms in dp, ps, Py and Pp(r).

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