S. Colilli

A proximity focusing RICH detector for kaon physics at Jefferson lab hall A

Important information on the LN interaction can be obtained from High Resolution Hypenuclear Spectroscopy experiments with electromagnetic probes. A challenging experiment on electroproduction of hypernuclei is scheduled for 2003 in Hall A at Jefferson Lab. One of the challenges is the high performance particle identification system needed. The signal is expected to be rare compared to the very high pion and proton backgrounds due to the small electron and kaon detection angles. The ‘‘standard’’ Hall A PID apparatus (TOF and two aerogel threshold Cherenkov detectors) does not provide sufficient suppression of the background. Simulations and calculations have shown that a RICH detector would solve the problem. A proximity focusing fluorocarbon/CsI detector similar to the ALICE RICH detector has been designed, built, tested and commissioned. The results show that the detector performs as expected. r 2003 Published by Elsevier Science B.V. PACS: 29.40.Ka; 85.60.Gz

Small animal imaging by single photon emission using pinhole and coded aperture collimation

The design of detectors for radio-imaging of small animals is challenging because of the high spatial resolution required, possibly coupled with high efficiency to allow dynamic studies. Spatial resolution and sensitivity are difficult to attain at the same time with single photon imaging techniques because collimators define and limit performance. In this paper we first describe a simple desktop gamma imager equipped with a pinhole collimator and based on a pixellated NaI(Tl) scintillator array coupled to a Hamamatsu R2486 PSPMT. The limits of such a system as well as the way to overcome them in future systems is shown next. Better light sampling at the anode level would allow better pixel identification for a higher number of pixels, which is one of the parameters defining image quality and improving spatial resolution. The performance of such a design is compared with other designs using other PSPMT types with different light sampling schemes at the anode level. Finally, we show how the substitution of the pinhole collimator with a coded aperture collimator can result in a substantial improvement in system sensitivity while maintaining very good spatial resolution, possibly at a sub-millimeter level. Calculations and simulations of a particular solution show that sensitivity can improve by a factor of nearly 30.

Scintillator and photodetector array optimization for functional breast imaging

Nuclear Medicine methods have been proposed as a means of imaging primary breast lesions and regional metastatic involvement based on tumor physiology. Recently, the positive predictive value of scintimammography using 99 Tc labelled SestaMIBI has been reported to be as high as 81%, with an associated negative predictive value of 97%. Visualization of small (o1 cm) lesions using scintimammography may be complicated, however, by the effects of overlying and underlying background uptake of MIBI in the breast soft tissue and the deterioration of lesion contrast with distance from the gamma camera. For these reasons dedicated compact gamma cameras have been proposed and successfully used. Nevertheless, the detection of very small tumors (o5–10 mm) is still very difficult. Many parameters affect the breast small tumors detection. The degree of pixellation of both the scintillator and photodetector is critical for the intrinsic position resolution of the detector and for the overall imaging performance. In this paper, we examine the basic imaging properties of systems using arrays of scintillators and pixellated photodetectors. The influence of readout systems is also taken into account. Simulations as well as preliminary experimental results are presented. r 2002 Published by Elsevier Science B.V.

Quantum efficiency measurement system for large area CsI photodetectors

A proximity focusing freon/CsI RICH detector has been built for kaon physics at Thomas Jefferson National Accelerator Facility (TJNAF or Jefferson Lab), Hall A. The Cherenkov photons are detected by a UV photosensitive CsI film which has been obtained by vacuum evaporation. A dedicated evaporation facility for large area photocathodes has been built for this task. A measuring system has been built to allow the evaluation of the absolute quantum efficiency (QE) just after the evaporation. The evaporation facility is described here, as well as the quantum efficiency measurement device. Results of the QE on-line measurements, for the first time on large area photocathodes, are reported.

Silica aerogel threshold Cherenkov counters for the JLab Hall A spectrometers: improvements and proposed modifications

Recently approved experiments at Jefferson Lab Hall A require a clean kaon identification in a large electron, pion, and proton background environment. To this end, improved performance is required of the silica aerogel threshold Cherenkov counters installed in the focal plane of the two Hall A spectrometers. In this paper we propose two strategies to improve the performance of the Cherenkov counters which presently use a hydrophilic aerogel radiator, and convey Cherenkov photons towards the photomultipliers by means of mirrors with a parabolic shape in one direction and flat in the other. The first strategy is aerogel baking. In the second strategy we propose a modification of the counter geometry by replacing the mirrors with a planar diffusing surface and by displacing in a different way the photomultipliers. Tests at CERN with a 5GeV/c multiparticle beam revealed that both the strategies are able to increase significantly the number of the detected Cherenkov photons and, therefore, the detector performance.

GEM tracker for high luminosity experiments at the JLab Hall A

A new large-area, lightweight tracker based on the GEM technology is under development for the upcoming experiments in Hall A at Jefferson Lab, where a longitudinally polarized electron beam of 11 GeV will be available in late 2013. This beam, combined with innovative polarized targets, will provide luminosity up to 1039/(s⋅cm2) opening exciting opportunities to investigate unexplored aspects of the inner structure of the nucleon and the dynamics of its constituents. The GEM tracker design is presented in this paper.

An online proton beam monitor for cancer therapy based on ionization chambers with micro pattern readout

A unique compact LINAC accelerator for proton therapy is under development in Italy within the TOP-IMPLART project. The proton beam will reach the kinetic energy of 230 MeV, it will have a widely variable current intensity (0.1?10 ?A, with average up to 3.5 nA) associated with a high pulse repetition frequency (1?3.5 ?s long pulses at 10?100 Hz). The TOP-IMPLART system will provide a fully active 3+1D dose delivery, that is longitudinal (energy modulation), transverse active spot scanning, and current intensity modulation. These accelerator features will permit a highly conformational dose distribution, which therefore requires an effective, online, beam monitor system with wide dynamic range, good sensitivity, adequate spatial resolution and rapid response. In order to fulfill these requisites a new device is under development for the monitoring of the beam intensity profile, its centroid and direction; it is based on transmission, segmented, ionization chambers with typical active area of 100 ? 100 mm2. Micro pattern x/y pad like design has been used for the readout plane in order to maximize the field uniformity, reduce the chamber thickness and obtain both beam coordinates on a single chamber. The chamber prototype operates in ionization region to minimize saturation and discharge effects. Simulations (based on FLUKA) have been carried on to study the perturbation of the chamber on the beam parameters and the effects on the delivered dose (on a water phantom). The charge collected in each channel is integrated by dedicated auto-ranging readout electronics: an original scheme has been developed in order to have an input dynamic range greater than 104 with sensitivity better than 3%. This is achieved by a dynamical adjustment of the integrating capacitance to the signal intensity.

RICH DETECTOR AT JEFFERSON LAB, DESIGN, PERFORMANCE AND PHYSICS RESULTS

Since 2004 the hadron spectrometer of Hall A at Jefferson Lab is equipped with a proximity focusing RICH. This detector is capable of identify kaon from pion and proton with an angular separation starting from 6 sigma at 2 GeV/c. The RICH design is conceptually similar to the ALICE HMPID RICH; it uses a C6F14 liquid radiator and a 300 nm layer of CsI deposited on the cathode pad plane of an asymmetric MWPC. The RICH has operated for the Hypernuclear Spectroscopy Experiment E94-107, which took data in the last two years. Design details and performance along with first physics results from the hypernuclear experiment are shortly presented.

Preliminary Evaluation of Compact Detectors for Hand-Held Gamma Cameras.

Hamamatsu Photonics has recently developed a new generation of compact Position Sensitive PhotoMultiplier Tubes (pspmt) based on metal channel dynode charge multiplication technology. The R5900 family now has a range of compact tubes that differ in the structure of the anode. The models considered in this paper, the C8 and M16, also differ in the photocathode active area. The C8 has a crossed plate anode configuration consisting of 4X + 4Y strips and an active area of 22 × 22 mm 2 while the M16 has a 4 × 4 anode array with a smaller active area of 18 × 18 mm 2 . In this paper we report our evaluation of the C8 and the M16 tubes for clinical imaging applications such as a hand-held gamma probe, multi-pspmt camera and for tomographic rings. To this aim, measurements of pulse height uniformity, inter-channel gain variation and anode cross talk were performed using a light source coupled to a 1 mm diameter optical fiber. Finally, the pspmts were optically coupled to three CsI(Tl) scintillating arrays with pixel size ranging between 1.5 × 1.5 mm 2 and 4.2 × 4.2 mm 2 to compare the imaging properties.

Hybrid silicon μstrip and GEM tracker for JLab hall-a high luminosity experiments

A new hybrid silicon μstrip and large area GEM (Gas Electron Multiplier) tracker is under development for the upcoming high luminosity (up to 1039 /s/cm2) experiments at the Hall-A of the JLab 12 GeV electron beam facility. The system consists of 2 small 10×20 cm2 silicon planes placed near the scattering chamber and 18 40×50 cm2 GEM modules that form larger chambers with variable active area depending on the experimental needs. Rather general purpose readout electronics has been designed for both detectors and can be adopted in other equipment. It consists of two active components: front-end cards, directly connected to the detector channels and a multi-purpose digitizer board (MPD). The front-end is based on existing 128 channels APV25-S1 chip developed in the framework of LHC experiments. The MPD handles 16 front-end cards (for a total of 2048 channels) and can be used in VME environments (also VME64x or VXS). It also provides: optical, Ethernet, USB. These resources permit to use MPD cards in different frameworks, ranging from small bench-top to large on-detector distributed systems. The GEM project is part of the CERN/RD51 collaboration activities. The system has been beam tested in late 2010 and 2011, some results are presented here.