The Small-Angle Scattering of X-Rays by Nitrogen

Abstract

An experimental study has been made of the scattering of x‐rays by nitrogen at various pressures and temperatures in the general region of the critical point. Particular attention was given to the scattering at small angles. Copper Kα‐radiation used with a single‐crystal spectrometer and narrow slits provided the means of attaining low values of sinθ/λ where 2θ is the scattering angle and λ the wave‐length of radiation. A qualitative demonstration of the effect of pressure and temperature upon the small‐angle scattering from a fixed volume of sample was made by observing at a fixed angle the amount of scattering from the sample as it was made to approach and then cross the liquid‐vapor transition curve. At 29 selected conditions of pressure and temperature, more complete patterns were taken in an attempt to make a quantitative application of theoretical expressions to obtain values of the isothermal compressibility and the sizes of regions of inhomogeneity which give rise to the small‐angle scattering. Values of compressibility from this work are roughly comparable to those obtained by other methods. The regions of inhomogeneity are found to be small at low temperatures, and they increase in size as the P—T conditions approach the critical region. Typical values for the radii of the regions of inhomogeneity are found to be 3.8A at 115°K and 18.7 atmospheres, and 8.1A at 128°K and 36.8 atmospheres.