F. Garibaldi

Measurement of the Neutral Weak Form Factors of the Proton

We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from the proton. The kinematic point [{l_angle}{theta}{sub lab }{r_angle}=12.3{degree} and {l_angle}Q{sup 2}{r_angle}=0.48 (GeV /c){sup 2} ] is chosen to provide sensitivity, at a level that is of theoretical interest, to the strange electric form factor G{sup s}{sub E} . The result, A={minus}14.5{plus_minus}2.2 ppm , is consistent with the electroweak standard model and no additional contributions from strange quarks. In particular, the measurement implies G{sup s}{sub E}+0.39G{sup s}{sub M}=0.023 {plus_minus}0.034(stat){plus_minus}0.022( syst){plus_minus}0.026({delta}G{sup n}{sub E}) , where the last uncertainty arises from the estimated uncertainty in the neutron electric form factor. {copyright} {ital 1999} {ital The American Physical Society}

Longitudinal and transverse responses in quasi-elastic electron scattering from 208Pb and 4He

Abstract Longitudinal and transverse response functions, R L and R T , have been obtained in inclusive quasi-elastic electron scattering from 4 He and 208 Pb, for momentum transfers between 300 and 650 MeV/ c and energy transfers up to 350 MeV. A quenching of R L , ∼ 14% in 4 He and ∼ 50% in 208 Pb has been observed. Interpretations in terms of correlations and modification of nucleon form factors in the nuclear medium are discussed.

Electronic detection of focused Cherenkov rings from aerogel

Abstract The recent development of highly transparent aerogel has permitted its use as a Cherenkov radiator in a focused (non-Rayleigh-scattered) mode. We report on the optical properties of this aerogel obtained by observation of Cherenkov rings with single-electron-sensitive phototubes. The dependence on aerogel radiator thickness of the number of Cherenkov ring hit points and background is shown and compared to expectations. A 5 cm thick radiator of this aerogel will permit π K identification up to 20 GeV/c.

The quasi-free 3He(e, e′p) reaction

The proton spectral function has experimentally been determined with the 3He(e, e′p) reaction for missing energies, 0<Em<70MeV, and recoil momenta, 0<PB<310 MeV/c. Experimental results are obtained for both the two-body, 3He(e, e′p)2H, and three-body breakup processes. Proton momentum density distributions, obtained in a PWIA analysis, are compared with theoretical calculations: Faddeev solutions with the RSC and Paris potentials, and variational calculations with various potentials, including those with a three-nucleon interaction term. Energy-weighted sum rule results are presented and compared with theoretical predictions. The coincidence cross sections are also compared with calculations which include the effects of final state interactions and meson exchange currents. Consistency of the results with PWIA is investigated in the framework of the Chew-Low extrapolation procedure.

Design of compact pinhole SPECT system based on flat panel PMT

The present development of new gamma imagers has allowed to realize detectors with ultra high spatial resolution and very compact size for PET as well as for SPET application. In this paper we analyze and discuss the possible design of new pinhole SPECT scanners based on heads which consist of flat panel PSPMT and different design of scintillation arrays like NaI(Tl), 1 mm pixel size, and CsI(Tl) multi layers array, mounted in off centered configuration to improve the intrinsic spatial resolution of the imagers. The results show that an array configuration 2/spl times/2 Hamamatsu flat panel PSPMTs coupled to NaI(Tl) scintillation array with 1 mm pixel size, represents the best trade off between compactness and spatial resolution of pinhole SPET scanner. The use of off centered CsI(Tl) scintillation array coupled to a single flat panel PSPMT allows to arrange a high sensitivity and very compact pinhole SPET scanner at very low cost only worsening of 50% spatial resolution than an Anger gamma camera pinhole SPECT.

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

Tumor SNR analysis in scintimammography by dedicated high contrast imager

The introduction of a new gamma camera fully dedicated to scintimammography (Single Photon Emission Mammography-SPEM), and more recently with a full breast FoV, allowed to make clinical examination in cranio-caudal projection like in RX-mammography, with breast mildly compressed. Such cameras are based on pixellated scintillation array and position sensitive photomultiplier (PSPMT). Reducing the collimator-tumor distance, the geometric spatial resolution and contrast was enhanced. Unfortunately, due to the scintimammographic low counting, poor contrast images are still obtained, in particular for small tumor. The aim of this paper is to evaluate how a camera based on pixellated detector can improve the SNR values for small tumor by an effective correction of the spatial response. The procedure is based on good pixel identification. A Small Gamma Camera (SGC) was arranged using metal channel dynode PSPMT photomultiplier (Hamamatsu R7600-C8) coupled to different CsI (Tl) scintillator array, with field of view (FoV) with an all purpose collimator. This PSPMT kind drastically reduces the charge spread improving the intrinsic characteristics of the imager. The dimensions of the CsI (Tl) arrays were the same of PSPMT active area (22/spl times/22 mm/sup 2/). Considering the very high intrinsic spatial resolution, a look up table was realized to accurately correct the gain and spatial non-uniformities. We used a breast and torso phantom to characterize the SNR as a function of scintillation pixel size, thickness of the breast, tumor size and depth. The data showed that the SNR depends principally on the match between the tumor and pixel size. In particular, for a 6 mm diameter tumor, the best SNR results were obtained by a 2/spl times/2 mm/sup 2/ pixelled array. For larger tumors, up to 10 mm diameter, a greater pixel size, like 30 mm/sup 2/ or 4/spl times/4 mm/sup 2/, optimizes the SNR value. We compared the results of this camera with the analogous ones obtained by a SPEM gamma camera and by a standard Anger Camera.

Evidence for short-range correlations in O-16

Abstract The reaction 16 O( e , e ′ pp ) 14 C has been investigated at three values of the transferred energy ω . The differential cross sections were determined as a function of the missing energy and the missing momentum. Evidence for short-range correlations in 16 O has been obtained from the transition to the ground state of 14 C. The cross sections for this transition are well reproduced by two independent parameter-free microscopic calculations. The results of both calculations show that the reaction is dominated by knockout of a proton pair in a 1 S 0 state, driven by short-range-correlations.

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.

Custom breast phantom for an accurate tumor SNR analysis

The capability of the scintimammography to diagnose subcentimeters sized tumors was increased by the employment of a dedicated gamma camera. The introduction of small field of view camera, based on pixellated scintillation array and position sensitive photomultiplier, allowed to enhance the geometric spatial resolution and contrast of the images due to reduced collimator-tumor distance. The aim of this paper is to investigate the realistic possibility of T1a tumors detection (/spl sim/5 mm size) by comparing the signal-to-noise ratio (SNR) values obtained by different imagers. To this end, we have utilized a self-designed solid breast phantom with different sized hot spots (tumors). The phantom consists of seven disks with different thickness, molded from resin epoxy activated with Co/sup 57/ isotope. The overlapped disks represent a pendula breast with about 800 cc volume. Hot spots have not wall. One disk has holes to fit the hot spots representing the different sized lesions. The imagers utilized were: a standard Anger Camera and three different cameras based on scintillator array, CsI(Tl) or NaI(Tl), coupled to position sensitive photomultiplier with different technologies, to make detectors with field of view of 3 and 5 inch. The experimental results are supported by Monte Carlo simulation. It was highlighted how spatial resolution is a predominant element in tumor visibility and how background causes a reduction of the image contrast. All gamma cameras show close results at SNR values less than 10 and a full detectability of 8 mm tumor size. However, the results show the 5 mm tumor size is lower detection limit for all cameras.