Monitoring fluctuations at a synchrotron beamline using matched ion chambers: 1. modelling, data collection, and deduction of simple measures of association

The Bur, brightness and temporal characteristics of an x-ray source often d efine its utility for a specific experiment. However, there are numerous co ntributions to the statistics of a beam as observed by a particular detecto r and associated electronics. The significance of these fluctuations is oft en neglected, with a consequent loss of precision or accuracy of up to two orders of magnitude. An understanding of the detected statistics for a give n arrangement (and the means for optimizing this) can make the difference b etween a successful experiment and a much more limited investigation. We ex plain the method for measuring a wide variety of important statistical cont ributions to high accuracy, and draw attention to the statistical consequen ces of optimized monitoring of upstream signals, We discuss the use of two matched ion chambers on a monochromatized bending magnet beam at the Photon Factory, Tsukuba, Japan. This is an illustration of a general principle, a lso applicable to conventional fixed x-ray sources, for investigating simpl e measures of association, It allows the quantification of uncertainties of spectrometric measurements, and also allows these to be minimized. Copyrig ht (C) 2000 John Wiley & Sons, Ltd.