A. Rashevsky

Large area silicon drift detector for the ALICE experiment

AbstractTwohundredandsixtySiliconDriftDetectors(SDDs),eachwithanactiveareaof7:0 7:5cm 2 ; willequiptwoofthesixcylindricallayersofhighprecisionpositionsensitivedetectorsthatconstitutetheInnerTrackingSystem(ITS)oftheALICEexperimentatLHC.IndevelopingtheALICESDD,oneoftheobjectiveswastoworkoutarobustandredundantdesign.Unlikethecaseofsiliconmicrostriporpixeldetectors,asingledefectinaSDDmaybepropagatedthroughoutthewholedetector.Oneofthefeaturesofthedetectoristheoriginaldesignoftheintegratedvoltagedividerthatallowstoattenuateeffectivelysuchapropagationinthemostpracticalcases.Devicesimulationsandlaboratorymeasurementsarepresented.r 2002ElsevierScienceB.V.Allrightsreserved. 1. General detector characteristicsTheITSoftheALICEexperimentatLHCwillconsist of six cylindrical layers of high precisionposition-sensitive detectors. Two hundred andsixty identical SDDs will equip the 3rd and the4th layer, providingposition information in twodimensionsanddE(energy)sample[1,2].ThefinaldesignoftheALICESDD(calledALICE-D2)wascompleted in the year 2000 and up to now 40detectorshavebeenproduced.1.1. MaterialSpecial care was dedicated to the startingmaterial.Indeed,dopingfluctuationscausedistor-tions in the drift trajectories and deterioratesignificantly the detector position resolution inbothdirections[3–5].Thedetectorsarefabricatedon 5

Characteristics of the ALICE Silicon Drift Detector

A Silicon Drift Detector (SDD) with an active area of 7:0 � 7: 5c m 2 has been designed, produced and tested for the ALICE Inner Tracking System. The development of the SDD has been focused on the capability of the detector to work without an external support to the integrated high-voltage divider. Several features have been implemented in the design in order to increase the robustness and the long-term electrical stability of the detector. One of the prototypes has been tested in a pion beam at the CERN SPS. Preliminary results on the position resolution are given. # 2001 Elsevier Science B.V. All rights reserved.

A linear array silicon pixel detector: images of a mammographic test object and evaluation of delivered doses

We present images of a mammographic test object obtained using a linear array silicon pixel detector capable of single-photon counting. The detector pixel size was 200 x 300 microns2 and images were acquired by scanning the test object between the laminar detector and the x-ray source with a scanning step of 100 microns. A molybdenum anode tube was used with two different filtrations: 2 mm aluminium and 25 microns molybdenum. Conventional film-screen images were also obtained in order to compare spatial and contrast resolution. In our digital images it is possible to recognize low-contrast details having dimensions smaller than or equal to the dimensions of details visible by means of a clinical mammographic unit. The detection of microcalcifications smaller than 150 microns was possible only when using the Mo filtration. However a copper wire of 50 microns diameter was detectable when embedded in a simulated tissue. We discuss in detail the mean glandular doses (MGDs) delivered during the image acquisition. The MGDs necessary to obtain good-quality images are always smaller than at a conventional mammographic unit. Since MGDs depend on the x-ray spectrum, the dose reduction becomes larger when the applied spectrum is harder than in film-screen acquisition (Al filtration and 35 kVp).

The X-Ray Spectroscopic Performance of a Very Large Area Silicon Drift Detector

Silicon drift detectors (SDDs), due to their collection electrode geometry, have excellent noise performance and are well suited for low-energy X-ray spectroscopy applications. On the other hand these detectors, when dedicated to low energy X-ray spectroscopy, have a small sensitive area (from few square millimeters up to one square centimeter) to reduce the leakage current and its impact on the energy resolution. Because of this limitation they are rarely used in applications where large sensitive surfaces are required. We present the characterization of the spectroscopic performance of a very large sensitive area SDD (about 53 cm2) that has been realized in the frame of the LHC-ALICE experiment. We studied the energy resolution of the detector analyzing its dependence on both biasing conditions and temperature to evaluate the contribution of the different noise sources exploiting their relation with the shaping time. The experimental results obtained with 241 Am and 55 Fe sources show that the goal of a high energy resolution combined with large sensitive areas can be achieved.

Correction of dopant concentration fluctuation effects in silicon drift detectors

Abstract Dopant fluctuations in silicon wafers are responsible for systematic errors in the determination of the particle crossing point in silicon drift detectors. In this paper, we report on the first large-scale measurement of this effect by means of a particle beam. A significant improvement of the anodic resolution has been obtained by correcting for these systematic deviations.

Characterization of the ALICE Silicon Drift Detectors using an infrared laser

The Inner Tracking System of the ALICE experiment at LHC uses Silicon Drift Detectors in two cylindrical layers located at radial distance of ≈ 15 and ≈ 24 cm from the beam axis. The spatial resolution of silicon drift detectors can be strongly affected by inhomogeneities of the doping concentration, temperature effects and non-linearity of the drift potential distribution. Before the detector commissioning, an extensive study and characterization of all the produced detectors has been performed. For this purpose, a specific measuring station, based on a laser mapping system, has been developed.

An "edge-on" silicon strip detector for X-ray imaging

A silicon strip detector for the SYRMEP (SYncrotron Radiation for MEdical Physics) experiment has been designed and realised. The main features of this detector are AC-coupling through integrated coupling capacitors, DC biasing by means of a gated punch-through structure, bulk contact on the junction side through a forward-biased p/sup +/ implant and integrated fan-in on active silicon. Results of laboratory tests of the detector parameters, allowing a thorough evaluation of the technological solutions employed, are presented. The functionality of the detectors and the charge collection linearity have been tested with different /spl gamma/ sources, using a hybrid, low-noise front-end electronics.

A low-power CMOS ASIC for X-ray Silicon Drift Detectors low-noise pulse processing

We present an Application Specific Integrated Circuit (ASIC), named VEGA-1, designed and manufactured for low-power analog pulse processing of signals from Silicon Drift Detectors (SDDs). The VEGA-1 ASIC consists of an analog and a digital/mixed-signal section to achieve all the functionalities and specifications required for high-resolution X-ray spectroscopy in the energy range from 500 eV to 60 keV with low power consumption. The VEGA-1 ASIC has been designed and manufactured in 0.35-μm CMOS mixed-signal technology in single and 32-channel version with dimensions of 200 μm × 500 μm per channel. A minimum intrinsic ENC of 12 electrons r.m.s. at 3.6 μs shaping time and room temperature is measured for the ASIC without detector. The VEGA-1 has been tested with Q10-SDD designed in Trieste and fabricated at FBK, with an active area of 10 mm2 and a thickness of 450 μm. The aforementioned detector has an anode current of about 180 pA at +22°C. A minimum Equivalent Noise Charge (ENC) of 16 electrons r.m.s. at 3.0 μs shaping time and −30°C has been demonstrated with a total measured power consumption of 482 μW.

Phase Contrast Imaging in the Field of Mammography

It is very well known that imaging low contrast details in soft tissues is the main limitation of conventional X-ray radiology. Phase contrast imaging overcomes this limitation. Up to now, however, all the applications of this technique required high radiation doses, raising several questions about its utilisation in medical radiology.

The digital mammography program at the SR light source in Trieste

A synchrotron radiation beamline devoted to medical imaging has been built by the SYRMEP collaboration at Elettra in Trieste, Italy, and is now in operation. The SYRMEP imaging system is based on the combination of a monochromatic, laminar X-ray beam, with a laminar, high-efficiency pixel silicon detector. To image soft tissue, including small, low-contrast details, as in mammography, beam energies should be chosen in the range from 15 keV to 30 keV and the detector should be capable of single-photon counting. The SYRMEP beamline originates from a bending magnet light port and consists basically of a Be window, a slit system and a Si(1,1,1) crystal monochromator. The experimental area is equipped with a radiation flux monitor, a sample movement stage, and a positioning system holding the silicon detector. Images are obtained by keeping the detector stationary with respect to the beam and by scanning the sample through the beam itself. The current detector is a linear array of 200/spl times/300 /spl mu/m/sup 2/ pixels, each coupled to its electronic counting chain on a custom VLSI read-out chip. We present a summary of beam studies, and digital images of standard RMI 160 and RMI 180 Ackermann Mammographic phantoms. Results show the high contrast resolution, the good spatial resolution and the large dynamic range which constitute the defining characteristics of the SYRMEP imaging system.