Radiation Detectors and Low Noise Electronics

Research focus

The Peer review has evaluated this group as Excellent

An historical research activity, included in the research line “Radiation Detectors and Low Noise Electronics”, concerns the development of new types of Semiconductor Drift Detectors (SDDs). This kind of detector was co-invented in 1983 by Emilio Gatti (Professor Emeritus of our Department) and Pavel Rehak (of Brookhaven National Laboratory). The following developments were carried out in a strict research cooperation between Politecnico di Milano, Max Planck Institute Halbleiterlabor of Munchen (Germany) and Brookhaven National Laboratory (USA). In particular, in cooperation with the quoted institutions and the Dipartimento di Ingegneria Nucleare of Politecnico di Milano, a new SDD (Controlled-Drift Detector) for X-ray spectroscopic imaging combining position and energy resolution with ultra-fast readout has been co-invented and patented in 1998. In the reporting period we made progress in the detector design evolving from the first test structures to fully working detectors with second and third generation devices. This detector was applied in experiments both at ELETTRA Sincrotrone Trieste for material analysis and biomedical imaging (with relevant results in Diffraction Enhanced Breast Imaging) and as scatter detector in a Compton telescope for gamma ray imaging (with the recording for the first time of the recoil electron track and of the specific energy loss within a single Silicon layer). In the reporting period the research has also been focused on the development of a new X-ray detector consisting in a ring-shaped monolithic array of SDDs (“droplet type”) with a hole laser-cut in the centre, specifically designed for XRF (X-Ray Fluorescence) “elemental mapping” applications. The X-ray excitation beam, focused by a polycapillary X-ray lens in a small and intense spot, reaches the sample going through central hole. This geometry allows the collection of a large fraction of the fluorescence emitted by the sample. A complete high resolution spectrometer based on this detector has also been developed which can reach an outstanding detection rate of 106 cps. This instrument, working in air, allows elemental mapping of samples not suitable for analyses with the SEM Micro-probe. The spectrometer is now widely used in material analyses, in particular in the field of cultural heritage. The research is also focused on the development of detectors for gamma-ray spectroscopy and imaging based on scintillators readout by SDDs. As replacement of the conventionally used photomultiplier tube, the SDD offers better quantum efficiency with the scintillation light, excellent electronics noise, better compactness and intrinsic immunity to magnetic fields. In this research, state-of-the art performances in gamma-ray spectroscopy have been achieved. When used in an Anger camera configuration, a position resolution of few hundreds microns has been achieved in gamma-ray imaging. This opens the opportunity to use this detector in many applications in astrophysics and in the medical imaging field. Innovative ionizing radiation detectors based on compound semiconductors (GaAs, CdTe, SiC) have also been designed and studied. In particular, Gallium Arsenide X-gamma ray detectors with the highest reported energy resolution have been developed in collaboration with the European Space Agency. Silicon Carbide detectors, produced using a proprietary technology, have been designed, manufactured and tested, demonstrating the possibility of X-ray spectroscopy with a semiconductor detector operating in the widest temperature range ever tried (20 to 100°C). Part of the research activity concerns the development of the electronics required for the acquisition and processing of the detector signals. In the reporting period a wide class of VLSI 307 circuits dedicated to the readout and processing of the signals from ionizing radiation detectors and optical photodetectors has been designed, characterized and employed in instrumentation. The ASIC circuits are based on innovative analog architectures for low-noise and low-power processing of the signals. Mixed analog/digital circuits are also developed for the processing and multiplexing of signals from detectors with large number of channels. The activity of VLSI design regards mainly applications in the field of high-energy physics, X-ray spectrometers, medical imaging detection systems (in collaboration with Siemens Medical), astrophysics experiments on satellite (in collaboration with ESA) as well as industrial applications in collaboration with international companies. The interest has also been focused on the digital electronic for nuclear spectroscopy. Signal processors for random pulses analysis have been designed, realized and tested with throughput in the 100kevents/sec range, whose performances are comparable or superior to state-of-the-art commercial designs. In a first implementation, a system (based on programmable logic FPGAField Programmable Gate Array and DSP-Digital Signal Processor technology) has been configured as a high resolution amplitude spectrometer with precision timing capabilities. Relevant improvements are the reduction of processing requirements, time-continuous processing operation and adaptive dynamic management of numeric filters length.

Dipartimento di afferenza

Dipartimento di Elettronica e Informazione (DEI)

Docenti afferenti

Antonio Longoni (full professor)
Giancarlo Ripamonti (full professor)
Marco Sampietro (full professor)
Giuseppe Bertuccio (associate professor)
Carlo Fiorini (associate professor)
Angelo Geraci (associate professor)
Giorgio Padovini (associate professor)
Federico Zaraga (associate professor)
Chiara Guazzoni (assistant professor)