Nuclear Instruments and Methods in Physics Research A 572 (2007) 328–329 Spectroscopic performances of a very large area silicon drift detector Gianluigi Zampa à , Alexander Rashevsky, Andrea Vacchi Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Padriciano 99, I-34012 Trieste, Italy Available online 17 November 2006 Abstract Silicon drift detectors (SDD) are known to reach extreme performances in spectroscopy applications but these devices have small active area (few cm 2 at most). We are involved in the development of very-large active area SDDs (53cm 2 ) dedicated to tracking with high position resolution in a very-high particle multiplicity environment. Here we present preliminary experimental results on X-ray spectra measured with front-end electronics optimized for energy resolution. r 2006 Elsevier B.V. All rights reserved. PACS: 29.30.Kv; 29.40.Gx Keywords: X- and g-ray spectroscopy; Tracking and position-sensitive detectors 1. Introduction A large number of silicon drift detectors (SDD) have been developed for spectroscopy applications because of their very-low anode capacitance. Present spectroscopy SDDs have a small size (few cm 2 ), hence it is difficult to use them in large sensitive area applications. Being involved in the design of a very-large active area SDD (53cm 2 ) for tracking applications (resolution of ’ 30 mm), we are interested in the spectroscopy performances of our device. The detector [1–3], 300 mm thick, is divided into two drift regions, each one biased by 291 cathodes (120 mm pitch). Both regions end with a collection zone made of an array of 256 anodes. Guard structures are used to gradually scale the high negative potentials of the drift cathodes to the ground ring, and an integrated divider [4] biases the whole detector. 2. Experimental setup The SDD is mounted on a printed circuit board that allows to adjust the bias of the collection zone. All bias lines, together with the high voltage supply of the drift region are properly filtered. The signal is readout by a Transistor Reset Preamplifier (TRP) that uses a low- capacitance JFET ðC GS ¼ 0:4pFÞ mounted close to the edge of the detector to minimize the stray capacitance. Four anodes are readout together to avoid signal leakage (the total capacitance is 200fF, the leakage current is 50pA at8 1C). The measurements are taken using a 241 Am source collimated by a 0:6mm hole in a lead block placed just above the anodes. Detector and front-end electronics are placed inside a climatic chamber (70; þ180  C range) which shields them from irradiated noise. 3. Preliminary results Fig. 1 shows the 241 Am spectrum measured at 16  C using a trapezoidal shaping with a rise/fall time of 1:2 ms and a flat top of 0:2 ms. Table 1 reports the energy and width of the peaks: those at 17.8 and 20.8 keV are complex ones, while the larger width of the 26.3 keV peak is due to low statistics. The energy resolution is about 0.81KeV FWHM (7.7% at 10.55keV). Measurements made at different shaping time show an excess of parallel noise, hence it is necessary to investigate the mechanisms that increase the leakage current fluctuations. We modeled spatial variations of the drift field, due to imperfections in ARTICLE IN PRESS www.elsevier.com/locate/nima 0168-9002/$-see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2006.10.200 à Corresponding author. E-mail address: gianluigi.zampa@ts.infn.it (G. Zampa).