The analysis of the data collected by the NA50 experiment in 1998, reported in this paper, extends and clarifies the pattern of the previously observed J/ψ anomalous suppression. This new measurement, besides providing a deeper understanding of the previous observations, reveals a steady significative decrease in the J/ψ production rate up to the most central Pb-Pb collisions. It clearly rules out the presently available conventional (hadronic) models of J/ψ suppression, which unanimously predict a saturation of the J/ψ rate for central Pb-Pb collisions. On the contrary and together with the sharp onset of the anomalous suppression previously reported, the new observation leads to a global production rate pattern which finds its natural explanation in the framework of the formation of a deconfined state of quarks and gluons. Accepted by Phys. Lett. B 1) Università del Piemonte Orientale, Alessandria and INFN-Torino, Italy 2) Laboratoire de Physique des Particules (LAPP), IN2P3-CNRS, Annecy-le-Vieux, France 3) Laboratoire de Physique Corpusculaire (LPC), Université Blaise Pascal, IN2P3-CNRS, Aubière, France 4) Institute of Atomic Physics (IFA), Bucharest, Romania 5) Università di Cagliari / INFN, Cagliari, Italy 6) CERN, Geneva, Switzerland 7) Laboratório de Instrumentação e F́ısica de Part́ıculas (LIP), Lisbon, Portugal 8) Institute for Nuclear Research (INR), Moscow, Russia 9) Institut de Physique Nucléaire de Orsay (IPNO), Université Paris-Sud, IN2P3-CNRS, Orsay, France 10) Laboratoire de Physique Nucléaire des Hautes Energies (LPNHE), Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France 11) Università di Torino / INFN, Torino, Italy 12) Institut de Physique Nucléaire de Lyon (IPNL), Université Claude Bernard, IN2P3-CNRS, Villeurbanne, France 13) Yerevan Physics Institute (YerPhI), Yerevan, Armenia a) Also at UCEH, Universidade do Algarve, Faro, Portugal b) Also at IST, Universidade Técnica de Lisboa, Lisbon, Portugal c) Now at CERN, Geneva, Switzerland d) Now at FPNT, University of Mining and Metallurgy, Cracow, Poland e) On leave of absence from YerPhI, Yerevan, Armenia f) Also at University of Wuppertal, Wuppertal, Germany

In-vivo and in-situ measurement of the radiation dose administered during brachytherapy faces several technical challenges, requiring a very compact, tissue-equivalent, linear and highly sensitive dosimeter, particularly in low-dose rate brachytherapy procedures, which use radioactive seeds with low energy and low dose deposition rate. In this work we present a scintillating optical fiber dosimeter composed of a flexible sensitive probe and a dedicated electronic readout system based on silicon photomultiplier photodetection, capable of operating both in pulse and current modes. The performance of the scintillating fiber optic dosimeter was evaluated in low energy regimes, using an X-ray tube operating at voltages of 40–50kV and currents below 1mA, to assess minimum dose response of the scintillating fiber. The dosimeter shows a linear response with dose and is capable of detecting mGy dose variations like an ionization chamber. Besides fulfilling all the requirements for a dosimeter in brachytherapy, the high sensitivity of this device makes it a suitable candidate for application in low-dose rate brachytherapy. According to Peralta and Rego [1], the BCF-10 and BCF-60 scintillating optical fibers used in dosimetry exhibit high variations in their sensitivity for photon beams in the 25–100kVp energy range. Energy linearity for energies below 50keV needs to be further investigated, using monochromatic X-ray photons.

A small dimension, real-time readout dosimeter is desirable for specific applications in medical physics as for example, dose measurement in prostate brachytherapy. This particular radiotherapy procedure consists in the permanent deposition of low energy, low-dose and low-dose rate small sized radioactive seeds. We developed a scintillating fiber optic based dosimeter suitable for in-vivo, real-time low dose and low dose rate measurements. Due to the low scintillation light produced in the scintillating fiber, a high sensitive and high gain light detector is required. The Silicon Photomultipliers are an interesting option that allowed us to obtain good results in our studies.

In this work, the authors revisit the measurements of Trout and Kelley, and Simpkin and Dixon, by means of Monte Carlo simulations. Starting with a simple cylindrical homogeneous phantom, the authors introduce a more realistic phantom and the effect of the bucky in the simulations. The results indicate that optimised shielding methodologies should not neglect the attenuation and scattering by the patient plus bucky.

In this article, it is argued that current shielding methodologies can lead to an over-shielding of low-energy X-ray imaging facilities. Measurements of scattered air kerma rates in a mammography installation, including the effect of an anthropomorphic phantom of the patient, are presented. Detailed Monte Carlo calculations that support the measured results are also shown. Calculations for a mobile mammography installation, including the 'patient transmission factor', are presented and results are discussed.

Crystalline terbium-doped indium hydroxide structures were prepared by a rapid and efficient Microwave-Assisted Hydrothermal (MAH) method. Nanostructures were obtained at a low temperature. FE-SEM images confirm that these samples are composed of 3D nanostructures. XRD, optical diffuse reflectance and photoluminescence (PL) measurements were used to characterize the products. Emission spectra of terbium-doped indium hydroxide (In(OH)(3):xTb(3+)) samples under excitation (350.7 nm) presented broad band emission referent to the indium hydroxide matrix and D-5(4)-> F-7(6), D-5(4)-> F-7(5), D-5(4)-> F-7(4), and D-5(4)-> F-7(3) terbium transitions at 495, 550, 590 and 627 nm, respectively. Relative intensities of the Tb3+ emissions increased as the concentration of this ion increased from 0, 1, 2, 4 and 8 mol%, of Tb3+, but the luminescence is drastically quenched for the In(OH) 3 matrix. (C) 2012 Elsevier B.V. All rights reserved.

A radiation dosimeter for low dose rates based on a scintillating optical fiber coupled to a high gain photon-counting silicon photomultiplier (SiPM) for light readout was developed. The dosimeter satisfies most of the requirements for in-vivo, low dose-rate and real-time dosimetry. The device uses a small scintillator, is flexible and reasonably water-equivalent for photon energies above 100keV [1], [2]. Promising results were obtained when operating the device in current mode, detecting radiation from an X-ray tube in the 15–40kV range and for anode currents as low as a few μA. As single-photon detectors, the major drawback of SiPMs is their high dark count rate (noise), which is a problem for low dose rate measurements in single photon counting mode. This drawback can be reduced by cooling the SiPMs or by using a much more efficient proposed solution in which two SiPMs operate in coincidence mode reading out the same optical fiber, thus allowing the rejection of false events triggered by dark noise. We have implemented a simple low-cost system, with dedicated front-end electronics operating in pulse mode for coincidence detection. Performance studies of the dosimeter operating in current mode, as a function of the X-ray tube current and voltage, show good sensitivity even for low radiation dose. When operating in pulse mode under low activity gamma irradiation, the coincidence system was able to reduce the dark noise to a residual value.

Plastics have attractive characteristics that can be exploit in dosimetry. Nevertheless their application with low-energy photon beam is still limited. We aim to a better understanding of their capabilities at the radiology regime. A study of the characteristics of a polystyrene scintillator dosimeter, coupled to a WLS fiber is made in this work. The energy dependence for this detector is extracted for photon beams between 20 and 100 kVp and additional filtrations of 0.5, 1 and 4 mm of Al.

M.C. Abreu, B. Alessandro, C. Alexa, R. Arnaldi, M. Atayan, C. Baglin, A. Baldit, M. Bedjidian, S. Beolè, V. Boldea, P. Bordalo, S.R. Borenstein, G. Borges A. Bussière, L. Capelli, J. Castor, C. Castanier, B. Chaurand, B. Cheynis, E. Chiavassa, C. Cicalò, T. Claudino, M.P. Comets, N. Constans, S. Constantinescu, P. Cortese, J. Cruz, N. De Marco, A. De Falco, G. Dellacasa, A. Devaux, S. Dita, O. Drapier, B. Espagnon, J. Fargeix, P. Force, M. Gallio, Y.K. Gavrilov, C. Gerschel, P. Giubellino, M.B. Golubeva, M. Gonin, A.A. Grigorian, S. Grigorian, J.Y. Grossiord, F.F. Guber, A. Guichard, H. Gulkanyan, R. Hakobyan, R. Haroutunian, M. Idzik, D. Jouan, T.L. Karavitcheva, L. Kluberg, A.B. Kurepin, Y. Le Bornec, C. Lourenço, P. Macciotta, M. Mac Cormick, A. Marzari-Chiesa, M. Masera, A. Masoni, M. Monteno, A. Musso, P. Petiau, A. Piccotti, J.R. Pizzi, W. Prado da Silva , F. Prino, G. Puddu, C. Quintans, S. Ramos, L. Ramello, P. Rato Mendes, L. Riccati, A. Romana, H. Santos, P. Saturnini, E. Scalas, E. Scomparin S. Serci, R. Shahoyan, F. Sigaudo, S. Silva, M. Sitta, P. Sonderegger, X. Tarrago, N.S. Topilskaya, G.L. Usai, E. Vercellin, L. Villatte, N. Willis. 1 LAPP, CNRS-IN2P3, Annecy-le-Vieux, France. 2 LPC, Univ. Blaise Pascal and CNRS-IN2P3, Aubière, France. 3 IFA, Bucharest, Romania. 4 Università di Cagliari/INFN, Cagliari, Italy. 5 CERN, Geneva, Switzerland. 6 LIP, Lisbon, Portugal. 7 INR, Moscow, Russia. 8 IPN, Univ. de Paris-Sud and CNRS-IN2P3, Orsay, France. 9 LPNHE, Ecole Polytechnique and CNRS-IN2P3, Palaiseau, France. 10 Università di Torino/INFN, Torino, Italy. 11 IPN, Univ. Claude Bernard Lyon-I and CNRS-IN2P3, Villeurbanne, France. 12 YerPhI, Yerevan, Armenia. a) also at UCEH, Universidade de Algarve, Faro, Portugal b) also at IST, Universidade Técnica de Lisboa, Lisbon, Portugal c) on leave of absence from York College CUNY d) Universitá del Piemonte Orientale, Alessandria and INFN-Torino, Italy. e) also at Faculty of Physics and Nuclear Techniques, Academy of Mining and Metallurgy, Cracow, Poland f) now at UERJ, Rio de Janeiro, Brazil g) on leave of absence of YerPhI, Yerevan, Armenia

There are two key approaches in our CERN RD 39 Collaboration efforts to obtain ultra-radiation-hard Si detectors: (1) use of the charge/current injection to manipulate the detector internal electric field in such a way that it can be depleted at a modest bias voltage at cryogenic temperature range (<= 150 K), and (2) freezing out of the trapping centers that affects the CCE at cryogenic temperatures lower than that of the liquid nitrogen (LN2) temperature.In our first approach, we have developed the advanced radiation hard detectors using charge or current injection, the current injected diodes (CID). In a CID, the electric field is controlled by injected current, which is limited by the space charge, yielding a nearly uniform electric field in the detector, independent of the radiation fluence. In our second approach, we have developed models of radiation-induced trapping levels and the physics of their freezing out at cryogenic temperatures. (c) 2006 Elsevier B.V. All rights reserved.

The Clear-PEM scanner for positron emission mammography under development is described. The detector is based on pixelized LYSO crystals optically coupled to avalanche photodiodes and readout by a fast low-noise electronic system. A dedicated digital trigger (TGR) and data acquisition (DAQ) system is used for on-line selection of coincidence events with high efficiency, large bandwidth and small dead-time. A specialized gantry allows to perform exams of the breast and of the axilla. In this paper we present results of the measurement of detector modules that integrate the system under construction as well as the imaging performance estimated from Monte Carlo simulated data.

The GEANT4 Monte Carlo simulation and experimental characterization of the Siemens E.Cam Dual Head gamma camera hosted in the Particular Hospital of Algarve have been done. Imaging tests of thyroid and other phantoms have been made "in situ" and compared with the results obtained with the Monte Carlo simulation.

Radiation hardness up to 10(16) n(eq)/cm(2) is required in the future HEP experiments for most inner detectors. However, 10(16) n(eq)/cm(2) fluence is well beyond the radiation tolerance of even the most advanced semiconductor detectors fabricated by commonly adopted technologies: the carrier trapping will limit the charge collection depth to an effective range of 20-30 mu m regardless of depletion depth. Significant improvement of the radiation hardness of silicon sensors has been taken place within RD39. Fortunately the cryogenic tool we have been using provides us a convenient way to solve the detector charge collection efficiency (CCE) problem at SLHC radiation level (10(16) n(eq)/cm(2)). There are two key approaches in our efforts: (1) use of the charge/current injection to manipulate the detector internal electric field in such a way that it can be depleted at a modest bias voltage at cryogenic temperature range (<= 230K); and (2) freezing out of the trapping centers that affects the CCE at cryogenic temperatures lower than that of the LN2 temperature. In our first approach, we have developed the advanced radiation hard detectors using charge or current injection, the current injected diodes (CID). In a CID, the electric field is controlled by injected current, which is limited by the space charge, yielding a nearly uniform electric field in the detector, independent of the radiation fluence. In our second approach, we have developed models of radiation-induced trapping levels and the physics of their freezing out at cryogenic temperatures. In this approach, we intend to study the trapping effect at temperatures below LN2 temperature. A freeze-out of trapping can certainly help in the development of ultra-radiation hard Si detectors for SLHC. A detector CCE measurement system using ultra-fast picosecond laser with a He cryostat has been built at CERN. This system can be used to find out the practical cryogenic temperature range that can be used to freeze out the radiation-induced trapping levels, and it is ready for measurements on extremely heavily irradiated silicon detectors. Initial data from this system will be presented. (c) 2007 Elsevier B.V. All rights reserved.

We report measurements in a high-energy pion beam of the sensitivity of the edge region in “edgeless” planar silicon pad diode detectors diced through their contact implants. A large surface current on such an edge prevents the normal reverse biasing of the device, but the current can be sufficiently reduced by the use of a suitable cutting method, followed by edge treatment, and by operating the detector at low temperature. The depth of the dead layer at the diced edge is measured to be (12.5±8stat..±6syst.)μm.

The design and evaluation of the imaging system Clear-PEM for positron emission mammography, under development by the PEM Consortium within the framework of the Crystal Clear Collaboration at CERN, is presented. The proposed apparatus is based on fast, segmented, high atomic number radiation sensors with depth-of-interaction measurement capabilities and state-of-the-art data acquisition techniques. The camera consists of two compact and planar detector heads with adequate field-of-view dimensions for breast and axilla imaging. Low-noise integrated electronics provide signal amplification and analog multiplexing based on a new data-driven architecture. The coincidence trigger and data acquisition architecture makes extensive use of pipeline processing structures and multi-event memories for high efficiency up to a data acquisition rate of one million events/s. Experimental validation of the detection techniques, namely the basic properties of the radiation sensors and the ability to measure the depth-of-interaction of the incoming photons, are presented. System performance in terms of detection sensitivity, count-rates and reconstructed image spatial resolution were also evaluated by means of a detailed Monte Carlo simulation and an iterative image reconstruction algorithm.

First experimental results of the imaging system Clear-PEM for positron emission mammography, under development within the framework of the Crystal Clear Collaboration at CERN, are presented. The quality control procedures of crystal pixels, APD arrays and assembled detector modules are described. The detector module performance was characterized in detail. Results on measurements of light yield, energy resolution, depth-of-interaction and inter-channel cross-talk are discussed. The status of the development of the front-end electronics and of the data acquisition boards is reported.

Positron emission mammography (PEM) can offer a non-invasive method for the diagnosis of breast cancer. Metabolic images from PEM using 18F-fluoro-deoxy-glucose, contain unique information not available from conventional morphologic imaging techniques like X-ray radiography. In this work, the concept of Clear-PEM, the system presently developed in the frame of the Crystal Clear Collaboration at CERN, is described. Clear-PEM will be a dedicated scanner, offering better perspectives in terms of position resolution and detection sensitivity.

We report measurements in a high-energy beam of the sensitivity of the edge region in “edgeless” planar silicon pad diode detectors. The edgeless side of these rectangular diodes is formed by a cut and break through the contact implants. A large surface current on such an edge prevents the normal reverse biasing of this device above the full depletion voltage, but we have shown that the current can be sufficiently reduced by the use of a suitable cutting method, followed by edge treatment, and by operating the detector at a low temperature. A pair of these edgeless silicon diode pad sensors was exposed to the X5 high-energy pion beam at CERN, to determine the edge sensitivity. The signal of the detector pair triggered a reference telescope made of silicon microstrip detector modules. The gap width between the edgeless sensors, determined using the tracks measured by the reference telescope, was then compared with the results of precision metrology. It was concluded that the depth of the dead layer at the diced edge is compatible with zero within the statistical precision of ±8μm and systematic error of ±6μm.

The ISPA (Imaging Silicon Pixel Array)-tube is a position sensitive photon detector based on the hybrid technology. It detects light via a photocathode and an appropriate electric field accelerates the emitted photoelectrons towards a silicon pixel anode. This anode, finely segmented into pixel detectors provides binary images and allows for the self-triggering of the tube. Coupled to scintillating crystals, ISPA-tubes have been successfully tested in the field of gamma ray imaging, demonstrating real capabilities in both space and energy resolution. Recently, we have concentrated our efforts on the development of a compact and portable readout system based on new electronics and able to provide full control and real-time processing of ISPA-tubes. The system overview and the dedicated interface are presented in this paper.