R. Fratoni

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.

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.

High resolution and high sensitivity detectors for functional molecular imaging with radionuclides: the role of scintillator pixel size, photodetector anode pitch, collimation technique, and of the readout

Good spatial resolution and high sensitivity are required for detectors to be used for most of the bio-medical research and application (small animal imaging, detection of small tumors). In this paper we report on parameter optimization of single photon gamma rays detectors. Simulations and measurements were performed for designing and building detectors for early detection of small tumors in breast and in small animal imaging. Critical parameters are: contrast and signal to noise ratio (SNR). Intrinsic performances (spatial resolution, pixel identification etc.) were optimized first. Arrays of scintillators (NaI(Tl)) of different pixel pitch (down to the present technological limits for NaI(Tl) arrays fabrication (pitch of 2times2 mm2, 1.5times1.5 mm2 and 1.2times1.2 mm2 )) were coupled to arrays of PSPMTs with two anode readout element dimensions (6times6 mm2 and 3times3 mm2). Detectors having field of view of 100times100 mm2 and 150times200 mm2 were designed and built. An electronics system for reading out all the anode pad signals has been designed and constructed. Finally the collimation technique was considered. The limits of the coded aperture option have been studied. Preliminary results of these studies are presented