Array Of Silicon Drift Detectors Research Articles

Elemental mapping by means of an ultra-fast XRF spectrometer based on a novel high-performance monolithic array of Silicon Drift Detectors

This paper describes the design of a novel X-ray fluorescence spectrometer and presents its performance in elemental mapping applications. The spectrometer is based on a new ring-shaped monolithic array of four independent high-performance Silicon Drift Detectors (SDDs). These detectors and the innovative geometry of the spectrometer setup with a polycapillary lens coupled with a low-power X-ray generator allow reaching fast elemental mapping. Moreover, dedicated data acquisition system has been designed and developed in order to fully exploit the detection rate performance of the detector. The spectrometer can be used in several applications in the field of industrial technology, geology, scientific research and works of art analyses. In particular, in the field of bio-chemical sciences the spectrometer exploits its performance in imaging analysis of elements present in very low concentrations.

Performance Evaluation of an Advanced XRF Elemental Mapping System Featuring a Novel Ring-Shaped Monolithic Array of Silicon Drift Detectors

This paper introduces an ultra-fast X-ray fluorescence (XRF) spectrometer based on a novel ring-shaped semiconductor drift detector (SDD) and on a novel readout and processing electronics and discusses its performance. The new detector is based on 4 independent droplet type SDDs monolithically integrated on the same chip. The detector shape optimizes the collection angle of the fluorescence radiation. The X-ray excitation beam is focused on the sample by means of a polycapillary lens through the hole cut in the center of the detector. The droplet type SDD is characterized by a better energy resolution and a better peak-to-valley ratio with respect to the ones of conventional SDDs. The energy resolution is of the order of 140 eV FWHM on the Mn Kalpha line with 1 mus shaping time at -15degC and the peak-to-valley ratio is of the order of 6000. In order to fully exploit the detection rate performance of this detector we have developed a novel read-out electronic unit with selectable shaping time and on-board histogramming capability.

Silicon drift photodetectors for scintillation readout in medical imaging

In the attempt to improve system performances of position-sensitive γ-ray detectors with contemporary ease of use and compactness, the use of silicon photodetectors for scintillation readout has become of increasing interest. With respect to the long-established photomultiplier tubes (PMTs), silicon photodiodes (PDs) have the advantages of higher quantum efficiency (QE), smaller dimensions and lower biasing voltages. Avalanche photodiodes (APDs) combine the high QE and compactness of PDs with the benefit of a moderate avalanche multiplication gain, which reduced the electronics noise contribution. However, the statistical component is again affected by the statistics of the multiplication itself (noise factor), and the noise component is still appreciable mainly in the high energy range. Moreover, the sensitivity of the gain to temperature and biasing variations represents a potential practical drawback in the use of APDs arrays for the application. As an alternative to the mentioned photodetectors, silicon drift detectors (SDDs) have recently shown to achieve excellent performances in scintillation light detection. The SDD is a photodetector characterized by an area-independent, low-value output capacitance (∼100 fF), which is one of the major factors limiting the noise performances of the other silicon detectors’ technologies. SDDs used for CsI(Tl) scintillation readout have already shown to achieve state-of-the-art energy resolution in γ-ray spectroscopy, and monolithic arrays of SDDs have been recently experimented for the development of Anger cameras for high-resolution γ-ray imaging. In this work, is the performances achievable with SDDs in both energy and spatial resolution are discussed together with a review of the most important results achieved with first prototypes of SDD-based γ-ray detectors.

A large-area monolithic array of silicon drift detectors for medical imaging

Monolithic arrays of silicon drift detectors (SDDs) have been recently proposed to be used with scintillators for high-position-resolution γ-ray imaging applications. Thanks to the low electronics noise due to the small value of the output capacitance, the SDD offers better noise performances with respect to conventional photodiodes of the same geometry. Small monolithic arrays of SDDs have been used as photodetector of the scintillation light in a first prototype of Anger Camera for γ-ray imaging characterized by an intrinsic resolution better than 0.3 mm. In this work, we present a new large-area monolithic array of SDDs. It consists of a single chip composed of 77 single hexagonal units, each one with an active area of 8.7 mm 2, for a total active area of the device of 6.7 cm 2. It represents the largest monolithic array of SDDs with on-chip JFETs produced up to now for X-ray and γ-ray detection. The results achieved in the experimental characterization of a first prototype of the detector array are presented, both with X and visible photons. The energy resolution measured at 6 keV with the single unit of the array is of 142 eV at −10 °C, while a QE>90% was measured at λ=550 nm.

XRF spectrometers based on monolithic arrays of silicon drift detectors: elemental mapping analyses and advanced detector structures

We present a novel X-ray Fluorescence (XRF) spectrometer based on a ring-shaped monolithic array of silicon drift detectors (SDDs) with a hole laser-cut in the center and we show some examples of its application in elemental mapping analyzes. The X-ray excitation beam, focused by a polycapillary X-ray lens in a small and intense spot, reaches the sample going through the central hole of the detector chip. This geometry allows the collection of a large fraction of the fluorescence emitted by the sample and the reduction of the distance between the sample and the detector and, therefore of air absorption. These features, together with the high detection rate of the SDDs shorten the scanning time in elemental mapping. Some application examples of the new spectrometer in different research fields, from archaeometry to biology, are shown. Moreover, the paper introduces a new topology of the multi-element detector based on four SDDs monolithically integrated in a Silicon chip and surrounding a hole cut in its center. The structure of the four SDDs has been specifically designed to obtain very high energy-resolution and peak-to-background ratio. The first experimental results obtained with this detector are presented. It will equip a future version of the XRF spectrometer.

Monolithic arrays of silicon drift detectors for medical imaging applications and related CMOS readout electronics

Monolithic arrays of Silicon Drift Detectors (SDDs) have been recently proposed to be used with scintillators for high-position-resolution γ-ray imaging applications. Thanks to the low electronics noise due to the small value of the output capacitance, the SDD offers better performances with respect to conventional photodiodes of the same geometry. We show the results achieved with a small monolithic array of SDDs, each one with a front-end JFET integrated at its center, used as photodetector in a first prototype of Anger Camera. An intrinsic resolution better than 200 μm has been achieved with this prototype. Moreover, we describe a new monolithic array of SDDs composed of 77 single hexagonal units, each one with an active area of 8.7 mm 2, for a total active area of the device of 6.7 cm 2. Finally, the basic principles and the first results of the CMOS readout chip specifically designed for the readout of the signals from SDDs arrays are presented.

Silicon drift detectors coupled to CsI(Tl) scintillators for spaceborne gamma-ray detectors

Silicon Drift Detectors (SDDs), thanks to their peculiar low noise characteristics, have proven to be excellent photodetectors for CsI(Tl) scintillation light detection. Two basic detector configurations have been developed: either a single SDD or a monolithic array of SDDs coupled to a single CsI(Tl) crystal. A 16 independent detectors prototype is under construction, designed to work in conjunction with the MEGA Compton telescope prototype under development at MPE, Garching, Germany. A single SDD coupled to a CsI(Tl) crystal has also been tested as a monolithic detector with an extended energy range between 1.5 keV and 1 MeV. The SDD is used as a direct X-ray detector for low energy photons interacting in silicon and as a scintillation light photodetector for photons interacting in the crystal. The type of interaction is identified by means of pulse shape discrimination technique. Detectors based on an array of SDDs coupled to a single CsI(Tl) crystal have also been built. The readout of these detectors is based on the Anger camera technique, and submillimeter spatial resolution can be achieved. The two detectors' approaches and their applications will be described.

A monolithic array of 77 silicon drift detectors for X-ray spectroscopy and gamma-ray imaging applications

Monolithic arrays of Silicon Drift Detectors (SDDs) have been employed successfully in X-ray spectroscopy and /spl gamma/-ray imaging applications. Thanks to the low electronics noise achieved at short shaping time, the SDD is an ideal device for high-resolution and high-rate X-ray spectroscopy experiments at synchrotron sources. Moreover, small monolithic arrays of SDDs have also been used as photodetector of the scintillation light in a first prototype of Anger Camera for /spl gamma/-ray imaging characterized by an intrinsic resolution better than 0.3 mm. In this work we present a new large-area monolithic array of Silicon Drift Detectors. It consists of a single chip composed by 77 single hexagonal units, each one with a front-end JFET integrated in its center, arranged in a honeycomb configuration. Each SDD unit has an active area of 8.7 mm/sup 2/, for a total active area of the device of 6.7 cm/sup 2/. The linear dimensions of the active area are approximately 29/spl times/26 mm/sup 2/. It represents the largest monolithic array of SDDs with on-chip JFETs produced up to now for X-ray and /spl gamma/-ray detection. The results achieved in the experimental characterization of a first prototype of the detector array are presented. They include also the preliminary X-ray spectroscopy characterization of the SDD's units. The energy resolution measured at 6 keV with the single unit of the array is of 142eV at -10/spl deg/C.

A novel high‐resolution XRF spectrometer for elemental mapping based on a monolithic array of silicon drift detectors and on a polycapillary x‐ray lens

AbstractThis paper describes a novel x‐ray fluorescence spectrometer designed for elemental mapping applications. The spectrometer is based on a ring‐shaped monolithic array of silicon drift detectors (SDDs) with a hole in the center. The coaxial x‐ray excitation beam, focused by a polycapillary x‐ray lens, reaches the sample after passing through the central hole. This geometry optimizes the useful solid angle for collecting the fluorescence from the sample, while the optics maximizes the photon density in the excitation spot. These features, together with the very high detection rate of SDDs, allow a high scanning rate in elemental mapping to be achieved. Moreover, the spectroscopic resolution of SDDs (cooled by thermoelectric Peltier elements) is comparable to that of the classical Si(Li) liquid nitrogen‐cooled detectors. Several examples of applications of the novel spectrometer in various fields, from archeometry to biology, are presented. This paper introduces also a new multi‐element detector based on SDDs whose structure has been specifically optimized for very high resolution and very fast elemental mapping. Copyright © 2005 John Wiley & Sons, Ltd.

Small prototype of Anger camera with submillimeter position resolution

In this work we present a small prototype of Anger camera based on a monolithic array of silicon drift detectors (SDDs) used as photodetectors for a single CsI(Tl) scintillator crystal. This prototype, having a total sensitive area of about 1cm2, has been realized in order to evaluate the performances attainable in γ-ray imaging by using a SDD array instead of the more conventionally employed photomultiplier tubes. An intrinsic resolution better than 200μm has been measured with this camera. This result was achieved thanks to the extremely low electronics noise presented by the SDD units, fully exploited by the integration of the front-end junction field effect transistor directly on the detector chip. The main features of the detector as well as the results of its extended experimental characterization with 60 and 122 keV gamma rays are presented and discussed in the article. The present device has many potential applications in the field of medical imaging, in which outstanding position resolutions are essential.

A small prototype of LSO-SDD anger camera

In this paper, we present a small prototype of Anger camera based on a monolithic array of silicon drift detectors (SDDs) coupled to a single LSO scintillator. The SDD photodetector consists of an array of 19 hexagonal units with on-chip JFET and has about 1 cm/sup 2/ of total sensitive area. The SDD array was already successfully tested with a CsI(Tl) crystal. However, the long scintillation decay time of CsI(Tl) requires the use of a long shaping time to reduce the effect of the ballistic deficit. This requirement does not allow to fully exploit the low electronics noise of the SDD, which, on the contrary, reaches its minimum noise at short shaping times. Moreover, the use of a faster scintillator would improve the overall counting rate capability of the Anger Camera. On the other side, the LSO scintillator is characterized by a lower scintillation conversion efficiency with respect to CsI(Tl) and by a natural background. In this work the performances which could be expected from a LSO-SDD Anger Camera are first evaluated. Then, the results achieved in the experimental characterization of a prototype of this detector are presented. A position resolution better than 1 mm FWHM using a /sup 57/Co source (122 keV) has been measured.

Theoretical analysis and experimental characterization of a novel VLSI current-mode shaping cell for high-resolution spectroscopy

We propose a novel VLSI current-mode shaping cell for high-resolution spectroscopy. This innovative topology is based on the possibility of virtually increasing the physical value of an integrated resistor thus allowing to design shaping amplifiers with high-value (/spl sim/1-10 /spl mu/s) time constants with reduced area occupancy. In this paper, we present the main issues of the circuit design and a detailed analysis of the noise performance of the proposed topology. Profiting from this current-mode approach, we have designed in 0.8-/spl mu/m BiCMOS technology a fifth-order shaping amplifier (0.5-/spl mu/s shaping time) to be coupled to monolithic arrays of silicon drift detectors (SDDs) for high-resolution X-ray spectroscopy. The measured integral-non-linearity is below /spl plusmn/0.2% and the achieved energy resolution at the Mn K/spl alpha/ line (measured with the proposed shaping amplifier coupled to a single-channel 5 mm/sup 2/ Peltier-cooled SDD) is 159 eV FWHM fully comparable to the one obtained with a commercial shaping amplifier with the same time constant.

Calorimeter prototype based on silicon drift detectors coupled to scintillators for Compton telescopes application

The project of a new calorimeter module for Compton telescopes based on an array of silicon drift detectors (SDD) coupled to thallium activated cesium iodide (CsI(Tl)) scintillating crystals is presented. Because of their low output capacitance and the possibility to have the first amplifying stage directly integrated on chip, SDDs show better noise performances than traditional p-intrinsic-n (PIN) photodiodes. For this reason, SDDs coupled to scintillators show a higher energy resolution than similar systems based on PIN photodiodes. The detectors will be integrated in an array with read-out based on custom made ASIC’s built to match with the SDDs electrical properties. Shaped signals are digitally converted by a Digital Front-End Electronic Board which also takes care of ASICs handshaking. The system architecture is based on the PICsIT instrument on board the INTEGRAL satellite, at present fully operative. In this paper an overview of the instrument will be given and the status of the project will be reported.

Theoretical comparison between two different filtering techniques suitable for the VLSI spectroscopic amplifier ROTOR

The development of new detection systems based on arrays of Silicon Drift Detectors (SDD) used for new X-ray spectroscopy applications, like X-ray Holography and EXAFS experiments, requires the realization of suitable integrated low-noise electronics for the readout of the detector signals. Recently, a new VLSI time-variant signal processor called ROTOR has been developed. Despite its time-variant nature ROTOR is capable of correctly processing events randomly distributed along the time axis, thanks to the employment of the Concurrent Wheel Technique (CWT). Two different possible solutions for the ROTOR chip have been developed, both suitable for the CWT working mechanism. A theoretical comparison between the noise performances of the two filtering methods has been carried out and is presented in this work.

A monolithic array of silicon drift detectors coupled to a single scintillator for γ-ray imaging with sub-millimeter position resolution

In this work, we present a monolithic array of 19 silicon drift detectors (SDDs) used as photodetectors of the scintillation light in position sensitive γ-ray detectors. In this array, having a total sensitive area of about 1 cm 2, each SDD has a front-end JFET directly integrated on the detector chip, close to the collecting anode. The low electronic noise offered by each single unit allows to reach a sub-millimeter position resolution by coupling the SDD array to a single CsI(Tl) scintillator crystal in a “mini”-Anger camera scheme. In the paper, a detection module based on the SDD array is described and the noise performances are reported. Moreover, the results in terms of position resolution obtained with the mini Anger Camera realized with the SDD module are presented.

Resistive or capacitive charge-division readout for position-sensitive detectors

Two-point charge division is a typical technique for position measurements in linear multi electrode detectors (microstrips, multiwire proportional counters, silicon drift-detector arrays, and scintillators coupled to photodetectors). Only two preamplifiers, located at the right and the left ends of the detection array, are used, each of which receives a fraction of the charge produced by the ionizing event. Position is reconstructed comparing these charge fractions. In principle, either a resistive or a capacitive divider may be used to split the charge. The choice between such two different setups is not obvious. In fact, each of them shows advantages and disadvantages in terms of noise, signal propagation, and linearity. In this paper, we present a unified treatment for the capacitive and the resistive mechanisms of charge division that addresses the issues of this choice. As an example, the realistic setup of the multiwire position-sensitive proportional counter to be used in the TP-MUSIC III chamber of the ALADiN experiment at GSI is considered.

Gamma-ray imaging detectors based on silicon drift detectors arrays coupled to a single scintillator

Abstract Arrays of Silicon Drift Detectors (SDDs) coupled to a single scintillator, according to the Anger Camera scheme, can be successfully employed in gamma-ray imaging. The low value of output capacitance of a SDD allows to reach a lower electronics noise with respect to conventional silicon photodiodes used in scintillation detection. A small prototype of gamma camera with sub-millimeter resolution has been realized by using a monolithic array of small SDDs (5 mm2 each unit) with on-chip JFET. For the realization of gamma cameras of larger areas based on single units assembled in array, SDDs of 30 mm2 of area with external JFET have been also experimented.

A new XRF spectrometer based on a ring-shaped multi-element silicon drift detector and on X-ray capillary optics

This paper describes an innovative X-ray fluorescence spectrometer designed to achieve high-energy resolution, position resolution, and detection rate in elemental mapping applications. The spectrometer is based on a ring-shaped monolithic array of silicon drift detectors (SDDs) with a hole cut in its center. A coaxial X-ray excitation beam is transported to the sample through this hole. In this way, the solid angle for the collection of the X-ray fluorescence is optimized. Moreover, the X-ray beam is collimated on the sample using capillary optics in order to obtain high photon density in a small excitation spot. Detector, optics, and generator are assembled in a compact vacuum tightened unit. The structure of the proposed spectrometer and the first experimental results of its characterization are presented.

Transverse Polarization of $\Lambda$ Hyperons in Relativistic Au--Au Collisions at the AGS

We investigate the transverse polarization of A hyperons produced in 11.6 A GeV/c Au−Au collisions at the AGS. Experiment E896 yields results in two independent detector systems, a Silicon Drift Detector Array at midrapidity and a Distributed Drift Chamber at forward rapidity. In this article we focus on the mid-rapidity measurements. The results reveal a dependence of the polarization on the transverse momentum and Feynman-x of the A hyperons. The heavy-ion data are consistent with previous measurements in proton-proton and proton-nucleus collisions within statistical errors.

Spatial characterization of monolithic multi-element Silicon-Drift-Detectors for X-ray spectroscopic applications

Spatially resolved spectroscopic measurements with a 10 and 20 μm pencil beam have been performed on a monolithic 7-element Silicon-Drift-Detector (SDD). Detailed studies are shown of the modification of the spectroscopic response at pixel edges and pixel centre. The results give quantitative insight into the local SDD performance. A simple model predicts global properties (e.g. peak-to-background ratio) of larger SDD arrays, like the 61-element detector currently under development.