Fondazione Bruno Kessler (FBK) (Trento, Italy) has recently introduced High Density (HD) and Ultra High-Density (UHD) SiPMs, featuring very small micro-cell pitch. The high cell density is a very ...important factor to improve the linearity of the SiPM in high-dynamic-range applications, such as the scintillation light readout in high-energy gamma-ray spectroscopy and in prompt gamma imaging for proton therapy. The energy resolution at high energies is a trade-off between the excess noise factor caused by the non-linearity of the SiPM and the photon detection efficiency of the detector. To study these effects, we developed a new setup that simulates the LYSO light emission in response to gamma photons up to 30 MeV, using a pulsed light source. We measured the non-linearity and energy resolution vs. energy of the FBK RGB-HD e RGB-UHD SiPM technologies. We considered five different cell sizes, ranging from 10 μm up to 25 μm. With the UHD technology we were able to observe a remarkable reduction of the SiPM non-linearity, less than 5% at 5 MeV with 10 μm cells, which should be compared to a non-linearity of 50% with 25 μm-cell HD-SiPMs. With the same setup, we also measured the different components of the energy resolution (intrinsic, statistical, detector and electronic noise) vs. cell size, over-voltage and energy and we separated the different sources of excess noise factor.
The improvement of the coincidence resolving time (CRT) is one of the key factors for the next generation of positron emission tomography (PET) scanners. Silicon photomultipliers (SiPMs) are strong ...candidates to substitute photo multipliers tubes because of their compactness, ruggedness and insensitivity to magnetic fields. In order to achieve the best CRT, the SiPM should have high PDE which can be obtained increasing the bias voltage. We recently improved the NUV SiPM technology, with the addition of a new substrate type that provides significantly lower afterpulsing probability (Low-AP). This enables to extend the maximum bias voltage and thus obtain higher PDE. Additionally, we implemented a lower electric field version (Low-F) to reduce the field-enhanced thermal generation components of the dark count rate. In this work we present results of energy and timing resolution for PET application, using LYSO scintillator crystals, and coupled with 3 x 3 mm super(2) NUV SiPMs of three types: non-Low-AP, Low-AP and Low-AP + Low-F. All the devices reach very similar energy resolutions, around 9.5 %, and close to the intrinsic limit of the LYSO. Concerning the timing resolution, we found that the Low-AP substrate achieves an improvement of the CRT of approximate 30 ps, confirmed with the Low-F. Using 4 x 4 mm super(2) Low-AP SiPMs coupled to 3 x 3 x 5 mm super(3) and 3.8 x 3.8 x 22 mm super(3) LYSO crystals we obtained CRTs of 130 and 200 ps FWHM, respectively.
Context.The theory of stellar evolution can be more closely tested if we have the opportunity to measure new quantities. Nowadays, observations of galactic RR Lyr stars are available on a time ...baseline exceeding 100 years. Therefore, we can exploit the possibility of investigating period changes, continuing the pioneering work started by V. P. Tsesevich in 1969. Aims.We collected the available times of maximum brightness of the galactic RR Lyr stars in the GEOS RR Lyr database. Moreover, we also started new observational projects, including surveys with automated telescopes, to characterise the O–C diagrams better. Methods.The database we built has proved to be a very powerful tool for tracing the period variations through the ages. We analyzed 123 stars showing a clear O–C pattern (constant, parabolic or erratic) by means of different least–squares methods. Results.Clear evidence of period increases or decreases at constant rates has been found, suggesting evolutionary effects. The median values are β = +0.14 d Myr-1 for the 27 stars showing a period increase and β = -0.20 d Myr-1 for the 21 stars showing a period decrease. The large number of RR Lyr stars showing a period decrease (i.e., blueward evolution) is a new and intriguing result. There is an excess of RR Lyr stars showing large, positive β values. Moreover, the observed β values are slightly larger than those predicted by theoretical models.
We present a detailed characterization of the active area uniformity of InGaAs/InP Single-Photon Avalanche Diodes (SPADs) from two different design iterations. Nonuniformity of the electric field ...within the device active area has been measured through 2-D scans of detection efficiency and timing response to a pulsed laser. Additionally, we measured the near-infrared luminescence emitted by hot carriers during the avalanche. The nonuniformity is stronger at lower excess bias, with much higher and nonuniform electric field at the edge of the active area than expected, and it is fainter at higher excess bias, due to the saturation of the avalanche triggering efficiency. The main drawbacks are that the detection efficiency is position dependent when the SPAD is not fiber pigtailed and that the temporal response is worse, because of the nonuniform delay in the avalanche build-up across the SPAD active area.
BACKGROUND: Fluorescein is a fluorescent tracer that can be used for many applications. It is able to accumulate in brain areas with blood-brain barrier disruption, and thus it can be considered an ...ideal dye for intraoperative visualization of high-grade gliomas (HGG). We report the preliminary results of a phase II trail (FLUOGLIO) on a new fluorescein-guided technique to remove HHG with a dedicated filter on the surgical microscope. METHODS: In September 2011 we started a prospective phase II-trial (FLUOGLIO) to evaluated safety and obtain initial indications about efficacy of fluorescein-guided surgery for HGG. Patients with suspected HGG amenable to complete resection of contrast-enhancing area were eligible to participate in this study. This report is based on the analysis of the short- and long-term results in 28 consecutive patients with HGG (age range 45-74 years), enrolled since September 2011. Fluorescein was intravenous (i.v.) injected after intubation (5-10 mg/Kg). Tumor was removed with microsurgical technique and fluorescence visualization by BLU400 or YELLOW560 filters on Pentero microscope (Carl Zeiss, Germany). The study was approved by our Ethical Committee and registered on the European Regulatory Authorities website (EudraCT No. 2011-002527-18). RESULTS: Median pre-operative tumor volume was 33.1 cm3 (2.4-87.8 cm3). We found no adverse reaction to fluorescein administration. Tumor was completely removed in 80% of the patients. Median follow-up was 10 months. 6 months Progression-free Survival (PFS) and median survival were respectively 71.4 % and 11 months. CONCLUSION: Our analysis suggested that fluorescein-guided technique with a dedicated filter on the surgical microscope is safe and allows high-rate of complete resection of contrast-enhanced tumor at the early post-operative MRI.
The temperature stability of the SiPM signal output can be a crucial aspect in many applications. In a typical scenario where the detector is biased at a constant voltage, a temperature fluctuation ...determines a change in the breakdown voltage and consequently in the applied over-voltage. The latter impacts on all the parameters that determine the output signal such as gain, PDE and correlated noise probability. In this paper we show a detailed analysis of the dependence of these parameters versus the temperature. In particular, we analyze two cases in which the quantity of interest is the integrated charge or the signal amplitude, respectively. The model is applied to a 1 x 1 mm super(2) FBK RGB SiPM with 50 x 50 mu m super(2) cells showing a good agreement with the experimental data.
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