Absolute power measurements in small angle X-ray scattering with gas scattering calibration

The calibration of a high intensity X-ray beam from a rotating anode tube has been accomplished with the small angle scattering from three heavy gases used as primary standards because their scattering cross sections at zero angle could be calculated. The scattering of the three gases permitted calibration of the incident beam and geometry to ±2%. A scattering 10% in excess of that predicted from the thermodynamic relationships was observed for water, ethyl alcohol, xylene, and benzene. This excess was ascribed to double scattering. Possible application of these methods to determine the molecular weight of macromolecules was investigated. Scattering observed from solutions of metmyoglobin was within 3% of the predicted scattering. For ribonuclease a 35% excess over predicted scattering was observed and was ascribed to aggregation, of the molecules, shown by ultra centrifuge methods to occur in these solutions.