Nuclear Instruments and Methods in Physics Research A 477 (2002) 99–103 Beam test results of a drift velocity monitoring system for silicon drift detectors D. Nouais a, *, N. Boetti a , V. Bonvicini b , P. Cerello a , P. Giubellino a , R. Hern ! andez-Montoya a,1 , A. Kolojvari a,2 , G. Mazza a , J. Nissinen c , A. Rashevsky b , A. Rivetti d,a,3 , F. Tosello a , A. Vacchi b a INFN Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy b INFN Sezione di Trieste, Italy c Jyv . askyl . a University, Finland d Politecnico di Torino, Italy for the ALICE collaboration Abstract We report results on drift velocity monitoring using MOS charge injectors in silicon drift detectors obtained in beam test conditions. The correction of velocity variations as small as 0:03% caused by temperature variations of the order of 0:04Kallowedtogetanaveragespaceresolutionalongallthedriftpathof28 mm: Preliminaryresultdemonstratingthe possibility to correct for temperature gradients along the anode axis are also presented. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Position sensitive detector; Silicon detector; Drift detector; Drift velocity calibration; MOS charge injector 1. Introduction Silicon drift detectors (SDDs) are position sensitive detectors introduced during the 1980s. Their original charge transport scheme, parallel to the surfaces of the detector was proposed in Ref. [1]. The measurement of the transport time of the electrons generated by a traversing particle allows to determine one coordinate of its crossing point. The electrons drift essentially in a direction parallel to the surface of the detector with a constant velocity v under the effect of a uniform built-in electric field ~ E : v ¼ m e E ð1Þ where m e is the mobility parameter for the electrons. Then, the electrons are collected by an arrayofsmallsizeanodes(withatypicalpitchofa few hundreds of mm) perpendicular to the drift direction. The distribution of the amplitude of the anode signals produced by the electron cloud gives the coordinate perpendicular to the drift direction, *Corresponding author. Fax: +39-11-6699579. E-mail address: nouais@to.infn.it (D. Nouais). 1 Also at CINVESTAV Mexico City, Mexico. TRIL-ICTP program fellow. 2 Also at Cyclotron Laboratory, St. Petersburg, Russia. 3 Also at CERN Geneva, Switzerland. 0168-9002/02/$-see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0168-9002(01)01895-2