P. Barrillon

Characterization of a PET detector head based on continuous LYSO crystals and monolithic, 64-pixel silicon photomultiplier matrices

The characterization of a PET detector head based on continuous LYSO crystals and silicon photomultiplier (SiPM) arrays as photodetectors has been carried out for its use in the development of a small animal PET prototype. The detector heads are composed of a continuous crystal and a SiPM matrix with 64 pixels in a common substrate, fabricated specifically for this project. Three crystals of 12 mm × 12 mm × 5 mm size with different types of painting have been tested: white, black and black on the sides but white on the back of the crystal. The best energy resolution, obtained with the white crystal, is 16% FWHM. The detector response is linear up to 1275 keV. Tests with different position determination algorithms have been carried out with the three crystals. The spatial resolution obtained with the center of gravity algorithm is around 0.9 mm FWHM for the three crystals. As expected, the use of this algorithm results in the displacement of the reconstructed position toward the center of the crystal, more pronounced in the case of the white crystal. A maximum likelihood algorithm has been tested that can reconstruct correctly the interaction position of the photons also in the case of the white crystal.

Energy, Timing and Position Resolution Studies With 16-Pixel Silicon Photomultiplier Matrices for Small Animal PET

A high resolution small animal PET scanner that employs Silicon Photomultiplier (SiPM) matrices as photodetectors is under development at the University of Pisa and INFN Pisa. The first SiPM matrices fabricated by the Center for Scientific and Technological Research, FBK-irst (Trento, Italy), are being evaluated for this purpose. The devices are composed of 16 (4 times4) pixel elements of 1 mmtimes1 mm in a common substrate. The first tests have been carried out employing the ASIC MAROC2 for the readout. Energy and timing resolution, and position determination tests have been performed coupling both pixellated and continuous LYSO scintillator crystals to the matrix, and the results have been compared with the ones obtained for single SiPMs. The first tests on position determination with continuous crystals and SiPM matrices have been performed. An intrinsic spatial resolution of 0.61 mm FWHM has been obtained.

Luminosity measurement at ATLAS - Development, construction and test of scintillating fibre prototype detectors

We are reporting about a scintillating fibre tracking detector which is proposed for the precise determination of the absolute luminosity of the CERN LHC at interaction point 1 where the ATLAS experiment is located. The detector needs to track protons elastically scattered under mu rad angles in direct vicinity to the LHC beam. It is based on square shaped scintillating plastic fibres read out by multianode photomultiplier tubes and is housed in Roman Pots. We describe the design and construction of prototype detectors and the results of a beam test experiment at DESY. The excellent detector performance established in this test validates the detector design and supports the feasibility of the proposed challenging method of luminosity measurement. (c) 2006 Elsevier B.V. All rights reserved.

MAROC, a generic photomultiplier readout chip

The MAROC ASICs family is dedicated to the readout of 64-channel Multi Anode PMT and similar detectors. Its main roles are to correct the gain spread of MAPMT channels thanks to an individual variable gain preamplifier and to discriminate the input signals (from 50fC i.e 1/3 photo-electron) in order to produce 64 trigger outputs. A multiplexed analog charge output is also available with a dynamic range around 10 pe (∼1.6 pC) and a 12 bit Wilkinson ADC is embedded. Three versions of this chip have been submitted. MAROC 2 is the production version for the ATLAS luminometer and MAROC3 is a version with lower dissipation and significant improvements concerning the charge (30 pe: ∼5 pC) and trigger (discrimination from 10fC). This third version showed very good characteristics that are presented here.

MAROC : Multi-Anode readout chip

MAROC is the readout chip designed for the ATLAS luminometer made of Roman pots. It is used to readout 64 channels multi-anode photomultipliers and supplies 64 trigger outputs and a multiplexed charge output. The second version of this ASIC was received during summer 2006. It has been thoroughly tested at LAL since. This paper presents the results obtained and shows that the performances were found in agreement with the main requirements.

Hadron beam test of a scintillating fibre tracker system for elastic scattering and luminosity measurement in ATLAS

A scintillating fibre tracker is proposed to measure elastic proton scattering at very small angles in the ATLAS experiment at CERN. The tracker will be located in so-called Roman Pot units at a distance of 240 m on each side of the ATLAS interaction point. An initial validation of the design choices was achieved in a beam test at DESY in a relatively low energy electron beam and using slow off-the-shelf electronics. Here we report on the results from a second beam test experiment carried out at CERN, where new detector prototypes were tested in a high energy hadron beam, using the first version of the custom designed front-end electronics. With a spatial resolution of 25 mu m an adequate tracking performance was obtained, under conditions which are similar to the situation at the LHC. In addition, the alignment method using so-called overlap detectors was studied and shown to have the expected precision. (Less)

Development of a 3D imaging calorimeter in lanthanum bromide for gamma-ray space astronomy

The new generation of high light-output inorganic scintillators i.e. cerium-doped lanthanum(III) bromide (LaBr3:Ce) show a promising future in application as a space-based γ-ray calorimeter. Its internal qualities such as good energy resolution or radiation tolerance are well suited for detection of γ-rays in the MeV range, thus providing access to, so far, understudied questions in physics of nucleosynthesis, the active Sun or astrophysical compact objects. For this purpose, under the project of creating a new Compton telescope prototype, we have studied the response of a detection module comprising a 5×5 cm2 area and 1 cm thick LaBr3:Ce crystal scintillator coupled to a 64 channel multi-anode photomultiplier read out by the ASIC MAROC. Measurements with various radioactive sources have been compared with detailed GEANT4 simulations that include the tracking of the near-UV photons produced in the scintillation crystal. The localization of the first interaction point of incident γ-rays have been studied from the measured charge distributions using an artificial neural network. Together with the other measured properties, the position resolution that we obtain makes this detector module very interesting for the next generation of space telescopes operating in the medium-energy γ-ray domain.

DEVELOPMENT OF A DETECTOR (ALFA) TO MEASURE THE ABSOLUTE LHC LUMINOSITY AT ATLAS

The ATLAS collaboration plans to determine the absolute luminosity of the CERN LHC at Interaction Point 1 by measuring the trajectory of protons elastically scattered at very small angles (μrad). A scintillating fibre tracker system called ALFA (Absolute Luminosity For ATLAS) is proposed for this measurement. Detector modules will be placed above and below the LHC beam axis in roman pot units at a distance of 240 m on cach side of the ATLAS interaction point. They allow the detectors to approach the beam axis to millimeter distance. Overlap detectors also based on the scintillating fibre technology, will measure the precise relative position of the two detector modules, Results obtained during beam tests at DESY and at CERN validate the detectors design and demonstrate the achievable resolution. We also report about radiation hardness studies of the scintillating fibres to estimate the lifetime of the ALFA system at different operating conditions of the LHC. (Less)

The readout electronic of EUSO-Balloon experiment

The EUSO-Balloon experiment is a pathfinder for the satellite mission JEM-EUSO whose goal will be to observe Extensive Air Showers produced in the atmosphere by the passage can detect fluorescent UV photons released by the EAS thanks to Multi-anode photomultipliers (MAPMT) arranged in 6 × 6 matrices inside Photo Detector Modules (PDM). A set of lenses is used to focus the photons on the PDM which can be compared to a UV camera taking pictures every 2.5 μs period (GTU: Gate Time Unit). The experiment consists in launching a balloon, at an altitude of 40 km, equipped with complete PDM and Data Processing systems. This project, supported by CNES and constructed by the JEM-EUSO collaboration, is meant to prove that the technology of such an instrument is possible and that the performance is satisfying, raising the Technical Readiness Level (TRL) of JEM-EUSO. Moreover, complex trigger algorithms will be assessed and the main back ground (night glow plus star light) will be studied. A complex readout electronic chain has been designed for the EUSO-Balloon project. It contains two elements: the 9 EC units and the 6 EC-ASIC boards. The EC unit includes four 64-channel Multi-Anode Photomultipliers and a set of pcbs used to supply the 14 different high voltages needed by the MAPMTs and to read out the analog anode signals. These signals are transmitted to the EC-ASIC boards which contain 6 SPACIROC ASICs each. During the year 2012, prototypes of each board were produced and tested successfully, leading to the production of the flight model PCBs in 2013.

Characteristics of a prototype matrix of Silicon PhotoMultipliers (SiPM)

This work reports on the electrical (static and dynamic) as well as on the optical characteristics of a prototype matrix of Silicon Photomultipliers (SiPM). The prototype matrix consists of 4 ? 4 SiPMs on the same substrat fabricated at FBK-irst (Trento, Italy). Each SiPM of the matrix has an area of 1 ? 1mm2 and it is composed of 625 microcells connected in parallel. Each microcell of the SiPM is a GM-APD (n+/p junction on P+ substrate) with an area of 40 ? 40 ?m2 connected in series with its integrated polysilicon quenching resistance. The static characteristics as breakdown voltage, quenching resistance, post-breakdown dark current as well as the dynamic characteristics as gain and dark count rate have been analysed. The photon detection efficiency as a function of wavelength and operation voltage has been also estimated.