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Abstract: The aim of this work is the characterization of a ∅ 9×9mm CsI:Tl scintillator at a wide temperature range of −40°C to +22°C. A tested crystal with dimensions of ∅ 9×9mm was coupled to a 16mm diameter large area Avalanche photodiode (LAAPD). The crystal and the LAAPD were cooled down in a cryostat with a built-in Peltier element. Properties such as the number of electron–hole pairs per 1MeV, the nonproportionality, the energy resolution and the intrinsic resolution were inspected with eight different peaking times – i.e., 0.6μs, 1.2μs, 2.4μs, 4.8μs, 7.2μs, 9μs, 14.4μs, 28.8μs – and discussed in terms of the light pulse shapes measured by a single photon method. [Copyright &y& Elsevier]

In our previous work, a very good time resolution recorded with a 4 × 4 × 20 mm³ LSO crystal coupled to a Pho- tonis XP2ODO photomultiplier was shown, which suggests that TOF-PET based on the LSO is a realistic proposition. k further improvement of the time resolution, due to the common light readout by the cluster of PMTs in the block detector, proposed by Kuhn et al., triggered our further study of the time resolution obtainable with the LSO crystals. In the present work, the optimization of timing using a leading-edge fast discriminator and a constant fraction discriminator was done and the results of the leading-edge timing were discussed in terms of the Hyman theory. In the second part of the study, the time resolution measurements and an optimization of the system realizing the light readout by two XP20D0 PMTs coupled to a common light diffuser were carried out for the 4 × 4 × 20 mm³ LSO crystal placed in various positions with respect to the PMTs. The results show that using a sum of signals and, in consequence, a better light collection from several PMTs improves timing and should allow good homogeneity of the time resolution over a whole surface of the detectors to be achieved. [ABSTRACT FROM AUTHOR]

The properties of CdWO4 (CWO) crystals in gamma spectrometry were studied. Several small samples of 10times10times3 mm size, typically used in CT X-ray detectors, were tested and then compared to the performance of a larger crystal of 20 mm in diameter and 20 mm in height. The light output, energy resolution, and nonproportionality of the CWO response versus gamma-ray energy, were measured and compared with those of a small BGO to discuss further the origin of the intrinsic resolution of pure undoped scintillating crystals. A high light output of 6500plusmn200 phe/MeV and a good energy resolution of 6.6plusmn0.2% for 662 keV gamma rays from a 137Cs source were measured for the small samples coupled to an XP3212 photomultiplier. Common nonproportionality curves and consequently common intrinsic resolutions of small CWO and BGO suggest that they represent fundamental characteristics of the heavy oxide scintillating material themselves [ABSTRACT FROM PUBLISHER]

Performances of new fast XP20Y0/DA and XP20Y0Q/DA 8 stage photomultipliers (PMTs) equipped with a screening grid at the anode were studied. The time jitter of the new PMTs was measured using a fast light pulser based on an XP22 light emitting diode. The timing properties in coincidence experiments were measured with BaF2, LSO, and LaCl3 : Ce crystals for 60Co and 22Na gamma rays and discussed in terms of the measured photoelectron numbers. Particularly, the normalized time resolutions to the number of photoelectrons measured with BaF2 crystals were comparable to that measured in the past with the XP2020Q in a superior dynode-timing mode. A significant improvement of timing up to a factor of 1.2 due to the grid at the anode was shown also in the measurements with LSO and LaCl3 :Ce crystals. [ABSTRACT FROM AUTHOR]

The intrinsic energy resolution and nonproportionality of the light yield as a function of gamma ray energies, in the energy range of 14 keV to 1.33 MeV, were studied for small BGO (Bi4Ge3O12)crystals at room and liquid nitrogen (LN2 )temperatures. The study showed that the intrinsic resolution of BGO and the light yield nonproportionality as a function of energy do not depend on the crystal temperature. High light outputs of 14000 ± 300 electron-hole pairs and energy resolution of 6.5% ± 0.2% for 662 keV gamma rays were measured with the 9 mm diameter, 4 mm thick crystals, coupled to large area avalanche photodiodes and cooled down to LN2 temperature. Special attention was paid to analyzing the energy resolution of the escape peaks, which were well separated from the full-energy peaks due to the good energy resolution of BGO at LN2 temperatures and the energy of bismuth KX-rays. The intrinsic energy resolution of the BGO crystal for escape peaks does not show deviations from analysis of total energy absorption photopeaks. This is in spite of the fact that the contributions of X-rays and Auger electron cascade in creation of escape peaks are much smaller than in full-energy peaks. In the small volume crystal, mainly electrons produced in the photoelectric absorption create the escape peaks. [ABSTRACT FROM AUTHOR]

The pure NaI crystal has been studied using a Large Area Avalanche Photodiode (LAAPD) at near liquid nitrogen (LN2) temperatures. The study showed a high light output of 44 000±4000 photons/MeV (ph/MeV), the energy resolution of 5.9±0.2% for 661.6 keV γ-rays from a 137Cs source and a good proportionality of the light yield versus γ-ray energy. It has been shown also that a cooled LAAPD is an excellent photodetector to study scintillators at near LN2 temperatures. [Copyright &y& Elsevier]