Tabulations are presented of molecular form factors F (x), tor values of.t = sin(tJ /2)1 A from 0 to 1.25 A -1, for liquid ,,:ate~ at eight temperatures b~t~een 4 °C andl200 °C and for the free water molecule. For bqUld water, x = 0 to 1.25 A 1, the tabulated values are interpolated from exper!menta1 values of Narten and Levy (1971). For~he free water molecule, x = 0 to 1.25 A -1, the tabulated values are interpolated from calculated values of . For x = 1.25to 10 9 A-I, the independent atomic scatterin~ hypothesis is assumed and the water molecular form factor F (x) is calculated from thel hydrogen and oxygen atomic form factors given by Hubbell and Overbo (1979). Tabl~s of coherent scattering cross sections, obtained by numerical integration of the ThoJnson formula, weighted by F2(X), are presented for liquid water at eight temperatures be~ween 4 °C and 200 °C and for the free water molecule, for photon energies 5 ke V to 1 MeiV.

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Single-scattered energy has been calculated for a water phantom, in a geometrical arrangement that approaches that of the dynamic spatial reconstructor. Recent data on the Rayleigh differential cross-sections of liquid water have been used. The ratio for single-scattered to transmitted radiation is found to be dependent upon incident energy: in the range 20 to 80 ke V, it varies from 0.32 to 0.16. The contribution of the Rayleigh effect to single scattering is of the order of 90% at 20 ke V and 50% at 80 ke V.

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