Modular Detector Research Articles

The LVD experiment as a low background facility in the Gran Sasso Laboratory

The Large Volume Detector (LVD) in the Gran Sasso Laboratory of INFN is a modular detector mainly devoted to search for neutrinos from core collapse super-novae. It is made of 1000 tons of liquid scintillator divided in 840 stainless steel tanks 1.5m3 each. We present the possibility for LVD to work both as a passive shield and moderator for the gamma and neutron background and as an active veto to reduce the higher energy background coming from muon induced neutrons. An inner region inside the LVD structure (‘LVD Core Facility’) can be identified, with a volume of about 30m3, with the neutron background typical of an underground laboratory placed at a much deeper site. This region can be realized with a negligible impact on the LVD operation and its sensitive mass. The LVD Core Facility could be effectively exploited by a compact experiment for the search of rare events, such as double beta decay or dark matter. A possible candidate could be a liquid Xenon double phase detector.

Dosimetric characterization with 62 MeV protons of a silicon-segmented detector for 2D dose verifications in radiotherapy

Due to the features of the modern radiotherapy techniques, namely intensity modulated radiation therapy and proton therapy, where high spatial dose gradients are often present, detectors to be employed for 2D dose verifications have to satisfy very narrow requirements. In particular they have to show high spatial resolution. In the framework of the European Integrated Project—Methods and Advanced Equipment for Simulation and Treatment in Radio-Oncology (MAESTRO, no. LSHC-CT-2004-503564), a dosimetric detector adequate for 2D pre-treatment dose verifications was developed. It is a modular detector, based on a monolithic silicon-segmented sensor, with an n-type implantation on an epitaxial p-type layer. Each pixel element is 2×2 mm 2 and the distance center-to-center is 3 mm. The sensor is composed of 21×21 pixels. In this paper, we report the dosimetric characterization of the system with a proton beam. The sensor was irradiated with 62 MeV protons for clinical treatments at INFN-Laboratori Nazionali del Sud (LNS) Catania. The studied parameters were repeatability of a same pixel, response linearity versus absorbed dose, and dose rate and dependence on field size. The obtained results are promising since the performances are within the project specifications.

Preliminary dosimetric characterization of a silicon segmented detector for 2D dose verifications in radiotherapy

Due to the features of modern radiotherapy techniques, namely Intensity Modulated Radiation Therapy (IMRT) and Stereotactic Treatments with photon fields, where high spatial dose gradient are often present, detectors to be employed for two-dimensional (2D) dose verifications have to satisfy very narrow requirements. In particular, they have to exhibit high spatial resolution. In the framework of the European Integrated Project MAESTRO, a dosimetric detector adequate for 2D pre-treatment dose verifications was developed. It is a modular detector based on a monolithic silicon segmented sensor, with a n-type implantation on an epitaxial p-type layer. The sensor is composed of 21×21 pixels with 2×2 mm 2 area and 3 mm center-to-center distance. In this paper we report the first preclinical dosimetric characterization of the detector. The sensor was irradiated with 6, 10, 25 MV photon beams from a linear accelerator (LINAC). The studied parameters were repeatability of a single channel, reproducibility between different matrix elements, response linearity vs. absorbed dose and dose rate dependence of sensitivity. Some preliminary tests on energy dependence were also performed. The obtained results are promising since almost all the channels have performances within the project specifications (repeatability <0.5%, reproducibility <1%, deviation from linearity <1%, dose rate dependence <1%).

A high resolution scintillating fiber tracker with SiPM readout

A novel modular high-resolution charged-particle tracking detector design using 250 μ m diameter, round, scintillating fibers and SiPM arrays for readout is presented. The fiber modules consist of eight layers of 128 fibers, mechanically stabilized by a carbon fiber/Rohacell foam structure. A prototype using scintillating fibers with a diameter of 300 μ m and two types of silicon photomultipliers has been tested in a 10 GeV proton beam in late October 2006 at the T9 PS-beamline, CERN. We present the measured spatial resolution, efficiency and signal-over-noise for this setup. The advantage of this tracker concept is a compact and modular design with low material budget and only little or no cooling requirements depending on the quality of the silicon photomultiplieres.

A Prototype Three-Dimensional Position Sensitive CdZnTe Detector Array

A new CdZnTe gamma-ray spectrometer system that employs two layers of modular detector arrays Is being developed under the collaboration between the University of Michigan and the Pacific Northwest National Labaratory (PNNL). Each layer can accommodate up to three by three 3-dimensional position sensitive CdZnTe gamma-ray spectrometers. This array system is based on the newly developed VAS_UM/TAT4 ASIC readout electronics. Each of the nine detector modules consists of a pixellated CdZnTe detector and a VAS_UM/TAT4 ASIC front-end board. Each 1.5times1.5times1.0 cm3 CdZnTe detector employs an array of 11 by 11 pixellated anodes and a planar cathode. The energy depositions and 3-dimensional positions of individual interactions of each incident gamma ray can be obtained from pulse amplitude, location of each pixel anode and the drift time of electrons. Ten detectors were tested individually and half of them achieved resolution of <1.0% FWHM at 662 keV for single-pixel events (~30% of all 662 keV full energy deposition events). Two of them were tested in a simple array to verify that the upgrade to an array system does not sacrifice the performance of individual detectors. Experimental results of individual detectors and a two-detector array system are presented, and possible causes for several worse performing detectors are discussed.

Design of a high-resolution gamma-ray detector module for tomography applications

We present a modular gamma-ray detector design for gamma-ray tomography applications. As a key electronic component we use the APD array S8550 of Hamamatsu Corp. with 4×8 single APD elements each of 1.6mm×1.6mm size. For this APD array we tested and evaluated different configurations of 2mm wide lutetium yttrium orthosilicate scintillation crystals. Emphasize was given to high counting efficiency and low dead time in order to secure applicability of the detector to tomography of objects with highly attenuating materials. For electronic processing, we designed a low-cost low-power charge-sensitive preamplifier circuit using commercially available operational amplifier ICs. The modular design of the detectors allows us to build up larger line or arc detectors.

Statistical reconstruction for x-ray CT systems with non-continuous detectors

We analyse the performance of statistical reconstruction (SR) methods when applied to non-continuous x-ray detectors. Robustness to projection gaps is required in x-ray CT systems with multiple detector modules or with defective detector pixels. In such situations, the advantage of statistical reconstruction is that it is able to ignore missing or faulty pixels and that it makes optimal use of the remaining line integrals. This potentially obviates the need to fill the sinogram discontinuities by interpolation or any other approximative pre-processing techniques. In this paper, we apply SR to cone beam projections of (i) a hypothetical modular detector micro-CT scanner and of (ii) a system with randomly located defective detector elements. For the modular-detector system, SR produces reconstruction volumes free of noticeable gap-induced artefacts as long as the location of detector gaps and selection of the scanning range provide complete object sampling in the central imaging plane. When applied to randomly located faulty detector elements, SR produces images free of substantial ring artefacts even for cases where defective pixels cover as much as 3% of the detector area.

Microelectronics technologies for new detectors in medical imaging

The use of silicon chips for instrumentation developments in elementary particle physics serves as an example for other applications and digital imaging detectors could find use in medical and molecular imaging. Attractive features are direct quantum conversion in a semiconductor matrix, innovative three-dimensional modular detector construction, multilayer devices, very fast signal processing, on-line data pre-processing and massive parallelism at the system level. Cost aspects of such semiconductor imager options have to be taken into account in the R&D phase. With the integrated electronics and high density interconnects in the Medipix development as an example, the ultimate aim of single photon imaging comes within reach.

A new study on the energy spectrum and composition of primary cosmic rays at energies ∼ 10 14–10 16 eV using the GRAPES-3 array at Ooty

Data collected with the 250-detector air shower array and the 560 m 2 area tracking muon detector, operated at Ooty in southern India by the GRAPES collaboration, have been analyzed to study the shape of the energy spectrum and the composition around the knee . It is shown that muon multiplicity distributions, observed with the highly modular muon detector, permit a relatively more reliable measurement of the composition of the primary flux which then helps in a more accurate reconstruction of the energy spectrum from the observed shower size spectrum. Some preliminary results are presented here.

A NEW STUDY ON THE ENERGY SPECTRUM AND COMPOSITION OF PRIMARY COSMIC RAY FLUX AT ENERGIES ~ 1014 – 1016 EV USING THE GRAPES-3 ARRAY AT OOTY

Data collected with the 217-detector air shower array and the 560 m2 area tracking muon detector, being operated at Ooty in southern India by the India-Japan (Tata Institute-Osaka City University) collaboration, GRAPES, have been analyzed to study the shape of the energy spectrum and the composition around the knee. It is shown that the muon multiplicity distribution, observed with the highly modular muon detector, permits a relatively reliable measurement on the composition of primary flux which then helps in a more accurate reconstruction of the energy spectrum from the observed shower size spectrum. The highlights of the GRAPES array, the analysis procedure and the results are presented.

Construction of a modular large-area neutron detector for the NSCL

A collaboration of ten institutions, including a large number of undergraduate schools, proposed and constructed a highly efficient large-area neutron detector. The modular neutron array (MoNA) is designed to detect high-energy neutrons in experiments with fast rare isotopes at the National Superconducting Cyclotron Laboratory. It consists of 144 individual detector modules of plastic scintillator, is position sensitive, and features multi-hit capability. The MoNA project involves undergraduate students from the collaborating colleges and universities and gives them the possibility to take part in research at the forefront of nuclear physics.

A Modular Phase-Frequency Detector Design with �2n? Linear Range of Operation

To extend the linearity range of the phase-frequency detector/charge pump (PFD/CP) circuit, a modular design for a novel PFD architecture is proposed. The new circuit yields a modular extension range of –2Nπ to 2Nπ, where N is an integer representing the order of the PFD/CP extension. The efficacy of the new PFD/CP is demonstrated by the improved frequency acquisition time obtained via closed-loop simulation. Hence, the developed architecture is a good candidate for phase-locked loops requiring the use of PFD/CP with a broad linear range of operation.

Neutron detectors for active interrogation of highly enriched uranium

We describe the results of our effort to optimize three neutron detector systems for active interrogation of highly enriched uranium: 1) a large-area detector for maximum absolute efficiency; 2) modular detectors for maximum flexibility in configuring a detector system for an application; and 3) a portable detector. All three systems contained /sup 3/He tubes, polyethylene to moderate the neutrons, and cadmium to filter out room-return thermal neutrons. The back and sides of the detectors were shielded with additional polyethylene or borated polyethylene. The electronics gated off the data acquisition during the interrogating pulse, either bremsstrahlung photons from an electron linac or neutrons from a DT generator. The sensitivity of each detector system depends on the distance between the detector and nuclear material as well as on the intervening material. We present representative data for several configurations showing the performance of each system.

Focus on Laboratory Equipment

Focus on Laboratory Equipment

A prototype modular detector design for high resolution positron emission mammography imaging

Current challenges facing us in developing dedicated position emission tomography (PET) system for metabolic breast mammography (PEM) and small animal (ANIPET) are to achieve high spatial resolution (less than 2 mm) and high efficiency. It is also crucial to extend the sensitive areas of PEM detectors to their periphery in order to overcome the difficulty in imaging near a patient's chest wall. This limitation of the periphery dead region was revealed in the clinical trials of our previously developed PEM-I system. In the new study, we developed prototype detectors by using position-sensitive photomultiplier tubes (PS-PMTs) and pixelated bismuth germanate (BGO) crystals with depth encoding scheme to detect and localize gamma rays. The procedures in crystal processing include cutting, polishing, encapsulating, separating, and re-gluing. We also developed front-end electronic circuits including high-voltage dividers, anode resistor chains, position readout circuits, and last dynode timing circuits. Methods for combining four PS-PMTs with simple X+, X-, Y+, Y- outputs have been developed to further simplify the position recording. The detectors were constructed in the structure of array (two in the system)-module (four in each array)-unit (four in each module). The basic unit of one crystal and one PS-PMT can be field replaceable. Our new prototype detectors show that the proposed PEM-II system has a spatial resolution of 1.8 mm (versus 2.8 mm in PEM-I), a timing resolution of 10.3 ns (versus 12 ns in PEM-I), and a field-of-view of 88 mm /spl times/ 88 mm (versus 64 mm /spl times/ 56 mm in PEM-I). Compared with our previous PEM-I system, it demonstrates that the design improves the spatial resolution, enhances the detector field-of-view, and significantly reduces the peripheral dead regions.

CHICSi—a compact ultra-high vacuum compatible detector system for nuclear reaction experiments at storage rings. III. readout system

(CHICSi) Celsius Heavy Ion Collaboration Si detector system is a high granularity, modular detector telescope array for operation around the cluster-jet target/circulating beam intersection of the CELSIUS storage ring at the The. Svedberg Laboratory in Uppsala, Sweden. It is able to provide identity and momentum vector of up to 100 charged particles and fragments from proton–nucleus and nucleus–nucleus collisions at intermediate energies, 50– 1000 A MeV . All detector telescopes as well as the major part of electronic readout system are placed inside the target chamber in ultra-high vacuum (UHV, 10 −9– 10 −7 Pa ). This requires Very Large Scale Integrated (VLSI) microchip for the spectroscopic signal processing and the generation and transport of digital control signals. Eighteen telescopes, read out with chip-on-board technique by ceramics Mother Boards (MB) and corresponding 18 microchips are mounted on a 450×45 mm 2 Grand Mother Board (GMB), processed on FR4 glass-fibre material. Each of these 28 GMB units contains a daisy-chain organisation of the VLSI chips and associated protection circuits. Analogue-to-digital conversion of the spectroscopic signals is performed on a board outside the chamber which is connected on one side to a power distribution board, directly attached to a UHV mounting flange, and on the other side to the VME-based data acquisition system (CHICSiDAQ). This in its turn is connected via a fibre-optic link to the general TSL acquisition system (SVEDAQ), and in this way data from auxiliary detector systems, read out in CAMAC mode, can be stored in coincidence with CHICSi data.

A gamma-ray tracking detector for molecular imaging

A design for a gamma-ray detector for molecular imaging is presented. The system is based on solid-state strip detector technology. The advantages of position sensitivity coupled with fine spectral resolution are exploited to produce a tracking detector for use with a variety of isotopes in nuclear medicine. Current design concepts employ both silicon and germanium layers to provide an energy range from 60 keV to >1 MeV. This allows a reference X-ray image to be collected simultaneously with the gamma-ray image providing accurate anatomical registration. The tracking ability of the gamma-ray detector allows ambiguities in the data set to be resolved which would otherwise cause events to be rejected in standard non-tracking system. Efficiency improvements that high solid angle coverage and the use of a higher proportion of events make time resolved imaging and multi-isotope work possible. A modular detector system, designed for viewing small animals has been accepted for funding.

Multichannel detector–collimator for powder diffraction measurements at energy scanning x-ray absorption spectroscopy synchrotron radiation beamlines for high-pressure and high-temperature applications

We describe a modular detector system suitable to intercept the diffracted x-ray radiation (Debye–Scherrer rings) in a transmission geometry setup at monochromatic tunable synchrotron radiation beamlines. The detector consists of several independent channels composed of a motorized front slit and a rear detector slit system which can be mounted in either a vertical or a horizontal configuration. The detectors are placed at fixed scattering angles 2θ and the diffraction scan is performed by tuning the monochromator energy. The availability of a multidetector system allows one to cover a wide range of scattering vectors with limited range energy scans. The photon sensitive elements are based on CdZnTe solid state detectors which are used at ambient temperature for high efficiency photon counting in the 10–60 keV range. In alternative, conventional NaI(Tl) scintillation detectors can be integrated in the setup. The system can be mounted in a high-resolution configuration and typical widths in the range ΔE/E≃10−3 have been obtained for Bragg peaks. In these conditions the sensitivity to changes in the lattice spacing is better than 10−4. This detector system fully complements the experimental devices usually available at x-ray absorption spectroscopy beamlines and the short range structural information obtained using the x-ray absorption fine structure technique. Typical applications include high-pressure and high-temperature investigations of condensed matter.

Large area avalanche photodiode detector array upgrade for a ruby-laser Thomson scattering system

A low-cost upgrade has been implemented on the Madison Symmetric Torus (MST) ruby-laser Thomson scattering (TS) system to increase spectral coverage and substantially improve the signal-to-noise ratio (SNR). The spectral resolution has been increased from five channels on the long-wavelength side to an 11-channel system, which covers both sides of the laser line. Coverage on both sides of the spectrum allows for more accurate detection of subtle changes in the distribution function, particularly relativistic spectral shifts of high-temperature plasmas during auxiliary current drive. The previous microchannel plate (MCP) detector was replaced with an array of modular large area avalanche photodiode detectors, which have approximately 16 times the quantum efficiency of the MCP detector. Scattered light collection has also been upgraded, allowing the radial viewing location of the TS system to be easily changed between plasma discharges. Improved SNR and upgraded light collection hardware in the Thomson scattering system have facilitated first-time measurements of the evolution of the electron temperature profile in the MST under a variety of discharge conditions, leading to increased understanding of the underlying dynamics of reversed-field pinch plasmas.

Anode position and last dynode timing circuits for dual-layer BGO scintillator with PS-PMT based modular PET detectors

New high spatial resolution positron emission tomography (PET) detectors for small animal and breast imaging have been developed. In these detectors, position-sensitive photomultipliers (R7600-C12) and dual-layer pixelated bismuth germanate (BGO) crystals are employed to detect and localize gamma rays. Modified high-voltage dividers with last dynode readout circuits, front-end anode position, and last dynode timing schemes have been investigated and developed for these detectors. Methods for combining four position-sensitive photomultipliers (PS-PMTs) with simple four (X/sup -/, X/sup +/, Y/sup -/, and Y/sup +/) outputs have been developed to further simplify the position processing. The front-end circuits are small so they can be fitted into the detector's structure. A prototype of two detector modules, each having two PS-PMTs with corresponding electronic circuits, has been built for evaluation. The crystal elements of 10/spl times/10 in the proximal layer and 9/spl times/9 in the distal can be clearly identified.