Monitoring fluctuations at a synchrotron beamline using matched ion chambers: 2. isolation of component noise sources, and application to attenuationmeasurements showing increased precision by two orders of magnitude

The significance of statistical fluctuations in a synchrotron beam is often neglected, with a consequent loss of precision or accuracy of up to two or ders of magnitude. We illustrate this for the specific example of an x-ray attenuation measurement, Since all x-ray measurements involve either scatte ring or absorption (or both), the net potential gain in precision is simila r for all such experiments, including crystallographic and XAFS determinati ons. We demonstrate the net gain with data obtained with two matched ion ch ambers on a monochromatized bending magnet beam at the Photon Factory, Tsuk uba, Japan. Isolating and measuring component contributions to the overall fluctuations allows a robust determination of the limiting experimental pre cision. This approach also determines the absolute incident flux without me asuring the absolute photon count. The type of statistical analysis describ ed is not only a post facto diagnostic tool but, by being incorporated into the experiment on-line, can provide a real-time optimizing intervention in the measurement process. Copyright (C) 2000 John Wiley & Sons, Ltd.