Monitoring Fluctuations at a Synchrotron Beam-line Using Matched Ion Chambers: 2. Isolation of Component Noise Sources, and Application to Attenuation Measurements 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 orders of magnitude. We illustrate this for the specific example of an X-ray attenuation measurement. Since all X-ray measurements involve either scattering or absorption (or both), the net potential gain in precision is similar for all such experiments, including crystallographic and XAFS determinations. We demonstrate the net gain with data obtained with two matched ion chambers on a monochromatised bending magnet beam at the Photon Factory, Tsukuba. Isolating and measuring component contributions to the overall fluctuations allows a robust determination of the limiting experimental precision. This approach also determines the absolute incident flux without measuring the absolute photon count. The type of statistical analysis described is not only a post-facto diagnostic tool but, by being incorporated into the experiment on-line, can provide a real-time optimising intervention in the measurement process.