Nuclear Instruments and Methods in Physics Research A 591 (2008) 163–166 Performance of a single photon counting microstrip detector for strip pitches down to 10 mm A. Bergamaschi à , Ch. Broennimann, R. Dinapoli, E. Eikenberry, F. Gozzo, B. Henrich, M. Kobas, P. Kraft, B. Patterson, B. Schmitt Paul Scherrer Institut, CH-5232 Villigen, Switzerland Available online 21 March 2008 Abstract The MYTHEN detector is a one-dimensional microstrip detector with single photon counting readout optimized for time resolved powder diffraction experiments at the Swiss Light Source (SLS). The system has been successfully tested for many different synchrotron radiation applications including phase contrast and tomographic imaging, small angle scattering, diffraction and time resolved pump and probe experiments for X-ray energies down to 5 keV and counting rate up to 3 MHz. The frontend electronics is designed in order to be coupled to 50 mm pitch microstrip sensors but some interest in enhancing the spatial resolution is arising for imaging and powder diffraction experiments. A test structure with strip pitches in the range 10–50 mm has been tested and the gain and noise on the readout electronics have been measured for the different strip pitches, observing no large difference down to 25 mm. Moreover, the effect of the charge sharing between neighboring strips on the spatial resolution has been quantified by measuring the Point Spread Function (PSF) of the system for the different pitches. r 2008 Elsevier B.V. All rights reserved. PACS: 29.40.Gx; 85.30.De; 87.57.cf Keywords: Silicon microstrip detector; Photon counting; Charge sharing 1. Introduction Powder diffraction synchrotron radiation experiments require detections systems with low noise, high dynamic range and high spatial resolution. These requirements can only be fulfilled by single photon counting systems with a high granularity. The MYTHEN detector has been designed in order to add to these characteristics the possibility of performing time resolved measurements by acquiring entire diffraction patterns over 601 in a few seconds [1]. A new version of the detector (Mythen II) has recently been installed at the Material Science beamline at the Swiss Light Source (SLS) covering 1201 with 24 modules, each consisting of a silicon microstrip sensor with 50 mm pitch, bonded to 10 custom designed ASICs operating in single photon counting mode. It offers a frame rate above 10 frames per second. Different settings of the readout electronics have been defined depending on the selected energy and rate of the radiation. From the preliminary tests, the performances of the detection system allow to detect energies down to 5 keV (minimum threshold 3 keV) and counting rates up to 3 MHz/channel (rate corrections are not needed up to 200 kHz/channel). The 8 mm long 50 mm pitched strips provide an angular resolution of about 0.0041. In the perspective of upgrading the Material Science beamline with an undulator, with smaller focus size than with the current optics, there is an interest in increasing the granularity of the detector at least in the forward direction. Moreover, the detection system has been successfully tested and will be used also for other applications like medical imaging and small angle scattering where a higher spatial resolution would give an improvement in the data quality ARTICLE IN PRESS www.elsevier.com/locate/nima 0168-9002/$ - see front matter r 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2008.03.048 à Corresponding author. Tel.: +41 56 3103227; fax: +41 56 3104362. E-mail address: anna.bergamaschi@psi.ch (A. Bergamaschi).