CRYSON
Introduction

Aa(s) : atomic scattering in vacuum.
As(s) : scattering from the excluded volume.
Ab(s) :scattering from the hydration shell.
rs : The solvent density (1010 cm-2)
drb : The contrast in the solvation shell (1010 cm-2)

The solvent density

r_s = r_0H2O.(1.-Y) + r_0D2O*Y
where

Y is the D₂O fraction (ranges from 0 to 1)
r_0H2O = 0.562 is the H₂O scattering length density (10**10 cm**-2)
r_0D2O = 6.404 is the D₂O scattering length density (10**10 cm**-2)

1- Svergun D.I., Richard S., Koch M.H.J., Sayers Z., Kuprin S. & Zaccai G. (1998) Protein hydration in solution: experimental observation by X-ray and neutron scattering. Proc. Natl. Acad. Sci. USA ,95, 2267-2272.