A. Braem

Feasibility of a novel design of high resolution parallax-free Compton enhanced PET scanner dedicated to brain research

A novel concept for a positron emission tomography (PET) camera module is proposed, which provides full 3D reconstruction with high resolution over the total detector volume, free of parallax errors. The key components are a matrix of long scintillator crystals and hybrid photon detectors (HPDs) with matched segmentation and integrated readout electronics. The HPDs read out the two ends of the scintillator package. Both excellent spatial (x, y, z) and energy resolution are obtained. The concept allows enhancing the detection efficiency by reconstructing a significant fraction of events which underwent Compton scattering in the crystals. The proof of concept will first be demonstrated with yttrium orthoaluminate perovskite (YAP):Ce crystals, but the final design will rely on other scintillators more adequate for PET applications (e.g. LSO:Ce or LaBr3:Ce). A promising application of the proposed camera module, which is currently under development, is a high resolution 3D brain PET camera with an axial field-of-view of approximately 15 cm dedicated to brain research. The design philosophy and performance predictions based on analytical calculations and Monte Carlo simulations are presented. Image correction and reconstruction tools required to operate this transmissionless device in a research environment are also discussed. Better or similar performance parameters were obtained compared to other known designs at lower fabrication cost. The axial geometrical concept also seems to be promising for applications such as positron emission mammography.

Final tests of the CsI-based Ring Imaging Detector for the ALICE experiment

We report on the final tests performed on a CsI-based RICH detector equipped with 2 C6F14 radiator trays and 4 photocathodes, each of 6438 cm 2 area. The overall performance of the detector is described, using different gas mixtures, in view of optimizing the photoelectron yield and the pad occupancy. Test results under magnetic field up to 0.9 T, photocathode homogeneity and stability are presented.

Technology of photocathode production

Abstract Thin film photocathodes have been developed both for gas and vacuum based photodetectors. Over the last years we have gained experience in fabricating large area reflective CsI and semi-transparent mono- and bialkali-cathodes, i.e. Rb 2 Te and K 2 CsSb. Today we are producing stable cathodes with excellent quantum efficiency for large MWPC based pad detectors and Hybrid Photodiodes on a routine basis. We give an overview of the technologies involved in the preparation of the substrates, the cathode processing and the encapsulation. The dedicated processing plants and instrumentation, required for monitoring and characterisation, is discussed.

The CsI based Ring Imaging Detector for the ALICE experiment: Technical description of a large prototype

We report on the design and construction of a CsI-RICH detector composed of four CsI photocathodes of 64]40 cm2 each, and two C 6 F 14 radiator trays of 133]41 cm2. A detailed description of the novel elements is given and the performance of the detector is illustrated with some basic results obtained during the tests at the beam. ( 1999 Elsevier Science B.V. All rights reserved.

Observation of the UV scintillation light from high energy electron showers in liquid xenon

Abstract The UV scintillation light in liquid xenon has been observed using silicon drift photodiodes. Measurements were carried out in a rectangular light cell of dimentions 7.4 × 7.4 × 60 cm3 using 5 GeV electrons. The photodiodes and the preamplifiers were immersed in the liquid. A high quantum efficiency for 175 nm UV light has been measured. The scintillation light yield is found to be (1.5 ± 0.6) × 104 photons per MeV of energy deposited in liquid xenon. A light attenuation lenght of ≈ 40 cm has been measured.

The mirror system of COMPASS RICH-1

The architecture and the properties of the mirror system of the COMPASS RICH-1 detector, composed by 116 spherical VUV reflecting units supported by a lightweight mechanical structure, are described.

Fast RICH detector with a cesium iodide photocathode at atmospheric pressure

Abstract CsI photocathodes of 30 × 30 cm 2 size have been operated in a fast RICH detector composed of a NaF radiator and a multiwire proportional chamber with a cathode pad readout. Results are presented from tests with a 3 GeV c proton beam. A Cherenkov angular resolution of 8 mrad is obtained by detecting a mean of 8 photoelectrons per ring. Methods are described for counting the Cherenkov photons and evaluating the differential quantum efficiency of the CsI photocathode. The results obtained with photons impinging at a large angle on the CsI layer are presented and discussed in comparison with higher quantum efficiencies observed under different experimental conditions.

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.

Identification of high p⊥ particles with the STAR-RICH detector

Abstract The STAR-RICH detector extends the particle identification capabilities of the STAR experiment for charged hadrons at mid-rapidity. This detector represents the first use of a proximity-focusing CsI-based RICH detector in a collider experiment. It provides identification of pions and kaons up to 3 GeV /c and protons up to 5 GeV /c . The characteristics and performance of the device in the inaugural RHIC run are described.

Microanalysis surface studies and photoemission properties of CsI photocathodes

We present recent results of the study of surface properties and quantum efficiency (QE) of CsI photocathodes prepared on various substrates. Microanalysis methods provide laterally resolved surface morphology and chemical composition of the photoemissive film. Integral measurements of the QE of CsI were done with a monochromator system and a RICH device. It was shown that CsI films deposited on large area Ni- or Ni-Au-coated printed circuit electrodes have a uniform crystalline structure and an average QE close to that reached on polished stainless steel. The films have a good stability in air over periods of Ih. On a microscopic scale of 3-30 mu m, the films exhibit nonuniform emission properties correlated with variations in the chemical composition.