Current saturation in free-air ionization chambers with chopped synchrotron radiation

Abstract

Saturation curves for free-air ionization chambers with electrode gap widths of 4.2, 8.4 and 18mm were obtained for 10 and 15keV undulator synchrotron radiation thinned with a 230Hz rotating-disk chopper. Ion recombination in free-air ionization chambers was found to be inversely proportional to the applied electric field, and an expression that satisfactorily reproduced the ion-recombination rate is determined. A comparison of the expressions for continuous and pulsed X-rays revealed that chopped high-intensity X-rays require a higher voltage to attain saturation when the product of the pulse width and electric field exceeds a value that depends on the X-ray energy. This behaviour was observed explicitly for 10keV X-rays in measurements with the ionization chamber placed before and after the chopper. © 2013 International Union of Crystallography Printed in Singapore-all rights reserved.