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We present results of ionizing radiation measurement using optical fibers and LYSO scintillator. The LYSO was used to detect the radiation and the silica fibers were used to deliver scintillation radiation to single photon counter.

Scintillators are widely used in ionization radiation detection. The light extraction efficiency and thus the effective light output of scintillators are limited by the total internal reflection due to their high refractive indices. Furthermore, scintillators have an approximate Lambertian profile for the spatial distribution of the light emission, which is detrimental to the collection of light. In this paper, hollow microlens arrays (HMLAs) composed of periodic arrangement of individual hollow shell hemispherical microlenses are proposed to achieve the directional light extraction enhancement of scintillators. The optical properties of HMLAs can be conveniently adjusted by varying the refractive index and the thickness of the shell layer. Simulation results reveal that the refractive index and the thickness of the shell of the individual hollow microlenses are the key parameters to achieve the control of the light output of scintillators. The measurement results of the prepared HMLAs-coated LYSO scintillator are consistent with the prediction of the numerical simulations. This scheme of directional light extraction enhancement by HMLAs is also applicable to other light-emitting devices that have the requirement of directional emission.

A compact hard X-ray camera has been developed to study the behavior of fast electrons accelerated by lower hybrid waves in the TST-2 spherical tokamak. The camera consists of a pinhole made of tungsten alloy, a thin resin window, a thin LYSO scintillator disk, 5 fiber optic light guides and 5 photomultiplier tubes and shields. The camera is installed on a tangential port, and two-dimensional images are obtained by rotating the system around the axis of the port on a shot by shot basis. The typical energy range is 10 - 250 keV, and the energy resolution is about 100% (FWHM) at 100 keV. The measured images of a lower hybrid wave driven plasma show bright region at the inboard side (i.e., high field side).

A high resolution small animal PET scanner that employs Silicon Photomultiplier (SiPM) matrices as photodetectors is under development at the University of Pisa and INFN Pisa. The first SiPM matrices fabricated by the Center for Scientific and Technological Research, FBK-irst (Trento, Italy), are being evaluated for this purpose. The devices are composed of 16 (4 times4) pixel elements of 1 mmtimes1 mm in a common substrate. The first tests have been carried out employing the ASIC MAROC2 for the readout. Energy and timing resolution, and position determination tests have been performed coupling both pixellated and continuous LYSO scintillator crystals to the matrix, and the results have been compared with the ones obtained for single SiPMs. The first tests on position determination with continuous crystals and SiPM matrices have been performed. An intrinsic spatial resolution of 0.61 mm FWHM has been obtained.

We have studied the performance of two multi-pixel Geiger-mode APDs (recently developed by the Centre of Perspective Technologies and Apparatus (CPTA) in Moscow) with 1×1 mm 2 and 3×3 mm 2 sensitive area as a readout for LSO and LYSO scintillator crystals. Energy and timing spectra were measured using a 22 Na γ-source. The results of this study allow us to conclude that this photodetector is a very promising candidate for PET applications.

We present measurements from a first prototype of a 1 mm3 resolution clinical PET camera dedicated to breast imaging. This first prototype consists of two cartridges of 8 detector layers. Each detector layer comprises 16 dual LYSO-PSAPD modules arranged side by side. The LYSO scintillator is an 8×8 array of 0.9×0.9×1 mm3 crystal pixels. Each array is coupled to a PSAPD. The modules are oriented edge-on with respect to the incoming 511 keV photons. The two cartridges thus contain 256 PSAPDs and 16,284 crystals each. The entire camera will have 2 imaging heads of 9 cartridges each.

The AX-PET is a new geometrical concept for a high resolution 3D PET scanner, based on matrices of axially oriented LYSO crystals interleaved by stacks of WLS, both individually read out by G-APDs. A PET demonstrator, based on two detector modules used in coincidence, is currently under construction.

The effective light attenuation length in thin bars of YAP:Ce and LYSO:Ce crystals has been studied for different coatings of the lateral surfaces of the scintillators. This physical parameter plays a key role in a novel 3D PET concept based on axial arrays of long scintillator bars read out at both ends by Hybrid Photodetectors (HPD). The parameter influences the spatial, energy, and time resolutions of such a device. The expected resolutions let the novel concept appear competitive compared to existing traditional PET devices. In this paper we show that the effective light attenuation length can be tuned to the desired value by wrapping the lateral surfaces of the crystals or by coating them with layers of Cr or Au of different thickness. The studies have been carried out with long YAP and LYSO scintillator bars, read out by standard photomultiplier tubes. Even though the novel PET device is planned to use different scintillators and HPD readout, the results described here prove the feasibility of an important aspect of the concept and explore the potential resolution of the device.