Nuclear Instruments and Methods in Physics Research A 487 (2002) 216–223 First tests of a Medipix-1 pixel detector for X-ray dynamic defectoscopy Daniel Vavrik a,b, *, Jan Jakubek c , Jan Visschers b , Stanislav Pospisil c , Cyril Ponchut d , Jaroslava Zemankova a a ITAM CAS, Prosecka 76, 190 00 Prague 9, Czech Republic b NIKHEF, Kruislaan 409, 1098 SJ Amsterdam, The Netherlands c FNSPE CTU, Brehova 7, CZ-11519 Praha 1, Czech Republic d ESRF, BP 220, F-38043 Grenoble Cedex, France Abstract Recent theoretical damage material models describe the dynamic development of voids and microcracks in materials under plastic deformation. For these models, experimental verification is needed. We propose direct and non- destructive observation of the propagation of material damage by measuring changes in transmission of X-rays penetrating a stressed material, using a photon-counting X-ray imager. The present contribution aims to demonstrate the applicability of silicon and gallium-arsenide devices for X-ray transmission measurements with a specimen of high- ductile aluminium alloy under study. The first experiments to determine the resolution and the sensitivity of the proposed method with the Medipix-1 pixel detector are presented. r 2002 Elsevier Science B.V. All rights reserved. PACS: 07.85.Fv; 42.79.Pw; 46.50.+a; 52.70.La; 62.20.Mk; 87.59.Hp Keywords: Defectoscopy; Fracture mechanics; Damage; Voids; X-ray and gamma-ray measurements; Semiconductor pixel detectors; Position- sensitive detectors; X- and gamma-ray detectors; Imaging detectors; X-ray radiography; Digital radiography 1. Introduction Catastrophic failures of different types of civil engineering structures may result from defects and cracks. Using Fracture Mechanics (FM) theory and Solid Mechanics theory we can improve the predictions for structure lifetime, reliability and safety from knowledge about existing defects and cracks and their time development. Stress concentrated around a crack tip in loaded structures is much higher than nominal (average) loading stress. Classical nonlinear FM results in false conclusions for advanced ductile materials [1]. Nowadays FM theories [2] take into account physical damage processes like nucleation and coalescence of voids appearing during the fracture. These processes are time and loading dependent. The mentioned theories need experimental verifi- cation of their assumptions. It is necessary to observe the internal material structural damage during the loading. Voids and microcrack sizes depend strongly on the stage of the damaging process and can grow *Corresponding author. ITAM CAS, Prosecka 76, 190 00 Prague 9, Czech Republic. E-mail address: vavrik@itam.cas.cz (D. Vavrik). 0168-9002/02/$-see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0168-9002(02)00968-3