INSTITUTE OF PHYSICS PUBLISHING MEASUREMENT SCIENCE AND TECHNOLOGY Meas. Sci. Technol. 16 (2005) 2280–2286 doi:10.1088/0957-0233/16/11/021 The correction of systematic image deformations inherent to two-dimensional proportional counters Mark N Kinnane 1 , Justin A Kimpton 1 , Martin D de Jonge 1 , Karoly Makonyi 2,3 and Christopher T Chantler 1,4 1 School of Physics, University of Melbourne, Victoria 3010, Australia 2 National Institute of Standards and Technology, Gaithersburg, MD 20899, USA Received 10 June 2005, in final form 26 August 2005 Published 4 October 2005 Online at stacks.iop.org/MST/16/2280 Abstract Two-dimensional backgammon configuration and multiwire gas proportional counters have been in use for decades in the field of x-ray physics for high-precision or high-flux experiments. Systematics inherent to this type of detector lead to image distortions that are often overlooked or extremely difficult to quantify. They are usually seen as intrinsic to the detector performance, leading to loss of resolution, linearity and signal-to-noise ratio. This work presents the signature, cause and resolution of several key distortions. The physics of the breakdown between the anode and cathode, false event position reconstruction due to the electronic detector response, and the effect of asymmetric field lines between the anode and cathode are developed. The position resolution of these types of detectors is demonstrated to be comparable to a charge-coupled device when used in the same experimental configuration. Keywords: x-ray beams, x-ray detectors, quantum electrodynamics, spectroscopy in atomic and molecular physics 1. Introduction Multi-wire gas proportional counters (MWPC) have had a long history of use in the field of experimental optics since Charpak’s development in 1968 [1, 2]. The charm quark and intermediate boson discoveries, which led to several Nobel prizes in particle physics, have particularly utilized these detector types [3–5]. This technology was rapidly applied to x-ray crystal diffraction and protein crystallography [6–8] The versatility of this detector has also allowed extensive development in the fields of: x-ray spectroscopy [9, 10]; time- resolved studies in biological structures [11, 12]; and the study of synchrotron x-ray sources [13]. Some useful reviews of the development of the MWPC have been compiled [14, 15]. In recent times, the MWPC has been used for high-precision tests of quantum electro-dynamics in the x-ray regime using electron beam ion traps (EBITs) [10, 16]. 3 Present address: Justus-Liebig-Universit¨ at Giessen, II, Physikalisches Institut, Giessen D-35392, Germany. 4 Author to whom any correspondence should be addressed. Many variations on the basic idea of highly charged wires acting as a conduit for charge produced by ionization events have been implemented ranging from the earliest Geiger–M¨ uller counters to the multiwire configuration of Charpak and the more modern microstrip detectors [17]. The recent popularity of charge-coupled devices (CCD) for two- dimensional x-ray event reconstruction is due to improved resolution resulting from reduced pixel size. However, the gas proportional counter has several advantages over CCDs: high photon detection efficiency over large energy ranges; individual photon, ‘event mode’ operation; and the cost effectiveness and simplicity of construction. The x-ray optics group at the University of Melbourne [18] have constructed and tested a detector using the ‘Jeu de Jacquet’ or backgammon [19] configuration x-ray detector. The detector configurations (dimensions, gas type, wire thickness, etc) were based upon previous work [20–22], with several improvements which allowed a detailed investigation of the detector operation. 0957-0233/05/112280+07$30.00 © 2005 IOP Publishing Ltd Printed in the UK 2280