Crosstalk calibration of multi-pixel photon counters using coherent states

We present a novel method of calibration of crosstalk probability for multi-pixel photon counters (MPPCs) based on the measurement of the normalized second-order intensity correlation function of coherent light. The method was tested for several MPPCs, and was shown to be advantageous over the traditional calibration method based on the measurements of the dark noise statistics. The method can be applied without the need of modification for different kinds of spatially resolved single photon detectors.Comment: 8 pages, 3 figures, 2 table

Photosensor Characterization for the Cherenkov Telescope Array: Silicon Photomultiplier versus Multi-Anode Photomultiplier Tube

Photomultiplier tube technology has been the photodetector of choice for the technique of imaging atmospheric Cherenkov telescopes since its birth more than 50 years ago. Recently, new types of photosensors are being contemplated for the next generation Cherenkov Telescope Array. It is envisioned that the array will be partly composed of telescopes using a Schwarzschild-Couder two mirror design never built before which has significantly improved optics. The camera of this novel optical design has a small plate scale which enables the use of compact photosensors. We present an extensive and detailed study of the two most promising devices being considered for this telescope design: the silicon photomultiplier and the multi-anode photomultiplier tube. We evaluated their most critical performance characteristics for imaging gamma-ray showers, and we present our results in a cohesive manner to clearly evaluate the advantages and disadvantages that both types of device have to offer in the context of GeV-TeV gamma-ray astronomy.Comment: submitted to SPIE Optics+Photonics proceeding

Novel Silicon Photomultipliers suitable for Dual-Mirror Small-Sized Telescopes of the Cherenkov Telescope Array

Many of the characteristics of Silicon Photomultipliers (SiPMs), such as high Photon Detection Efficiency (PDE), are well matched to the requirements of the cameras of the Small-Sized Telescopes (SSTs) proposed for the Cherenkov Telescope Array. In fact, compared to a single mirror, the double mirror Schwarzschild Couder configuration provides a much better Point Spread Function over a large field of view. It allows better correction of aberrations at large off axis angles and facilitates the construction of compact telescopes. Moreover, the small plate scale of the dual-mirror SSTs allows the use of SiPM detectors despite their small pixel sizes. These sensors have two further advantages compared to the Photo Multipliers Tubes: the low cost and the possibility to observe in very high Night Sky Background (NSB) light level without any damage. However, one area in which SiPM performance has required improvement is Optical CrossTalk (OCT), where multiple avalanches are induced by a single impinging photon. OCT, coupled with the typical NSB rate of 25 MCnts/s per pixel during Cherenkov observations, can place severe constraints on the triggering capability of the cameras. This paper describes the performance of novel Low Voltage Reverse (LVR) 2nd and 3rd generation Multi Pixel Photon Counters manufactured by Hamamatsu Photonics. These are designed to have both enhanced PDE and reduced OCT. Two 7 x 7 mm2 S14520 LVR2 MPPCs with 75 um microcells are tested and compared with detectors of the same pixel size with 50 um microcells. A comparative analysis of a 3 x 3 mm2 S14520 LVR2 device and an S14520 LVR3 device is also carried out, demonstrating that the LVR3 gives better photon detection in the 240 380 nm wavelength range. Finally, the effect of an infrared filter on the OCT is analysed.Comment: 17 pages, 17 figures, 2 tables. Submit to NIM-A Jurna

Development of ASIC for SiPM sensor readout

L'abstract è presente nell'allegato / the abstract is in the attachmen

Sistemas de tomografia por emissão de positrões para pequenos animais

The growing demand for PET scanners in preclinical studies combined with the high cost of those equipments increased the interest in the development of new high performance and low cost system, made possible due to the recent technological developments in the industry of radiation detection. Is this work, we present two low cost PET scanners. The first is the DRIM-PET, a PET scanner with improved spatial resolution through the determination of the depth-of-interaction of the photons in the detectors, correcting the parallax effect. The use of MPPCs and wavelength-shifting fibers for light detection allows to reduce the number of components, reducing the device cost. We present the performance characterization of an unitary cell of the DRIM-PET system, as a proof-of-concept, and we report a depth-of-interaction resolution of the order of 7mm. The other PET scanner presented is the EasyPET 3D, with capabilities of acquire volumetric images and execute spectroscopy. The use of a rotation system for the detecting cells allows to reduce the number of cells thus reducing the cost of the device, keeping high spatial resolution bellow 1.5mm, uniform along the FOV, which is variable up to 60mm. Image quality was evaluated using the NEMA NU-2008 standard, the commercial prototype for the first time shown and the first preclinical acquisitions are shown for 18F-FDG and 18F-NaF, for mouse brain and skeleton imaging, respectively. Finally, the development of a simulation toolkit written in GATE for the EasyPET prototype (2D), commercialized by the Italian company CAEN, SpA, allows students to perform simple tasks the simulate experimental procedures such as the evaluation of the effect of different coincidence time and energy windows for the reconstructed image, for radioactive sources at different locations within the FOV. The platform can be included in the official code EduGATE as a supplementary module.A crescente procura por tomógrafos PET para estudos pré-clínicos aliada ao elevado custo destes equipamentos, fez aumentar o interesse no desenvolvimento de novos sistemas de elevada performance a baixo custo, possibilitados pelos novos desenvolvimentos tecnológicos na industria de deteção de radiação. Dois sistemas de baixo custo são apresentados no âmbito deste trabalho. O primeiro é o DRIM-PET, um tomógrafo PET com melhorada resolução espacial através da determinação do ponto de interação da radiação nos detetores. A correção do efeito de paralaxe é feita usando MPPCs e fibras conversoras de luz para deteção da luz, mantendo um reduzido número de detetores. É apresentada a caracterização experimental de uma célula unitária do DRIM-PET como prova de conceito, onde a resolução espacial na determinação do ponto de interação obtida é da ordem de 7mm. O outro tomógrafo PET apresentado é o EasyPET 3D, com capacidade de aquisição de imagens em 3D e espectroscopia de raios. O uso de um sistema de rotação das células detectoras para aquisição de imagens permite reduzir o número de células, mantendo elevada resolução em posição, da ordem de 1.5mm, para um campo de visão variável até 60mm, reduzindo o custo do equipamento. A qualidade de imagem do dispositivo foi avaliada usando a norma NEMA NU-2008, o protótipo comercial apresentado e as primeiras aquisições pré-clínicas com 18F-FDG e 18F-NaF apresentadas, em imagens do cérebro e do esqueleto em ratos, respetivamente. Finalmente, o desenvolvimento de uma plataforma de simulação para o primeiro sistema EasyPET (2D), comercializado pela empresa CAEN, SpA, permite que estudantes executem tarefas simples que simulam as aquisições experimentais, como o efeito de diferentes janelas de tempo e energia para a imagem reconstruida, para fontes radioativas colocadas em diferentes localizações no FOV. A plataforma pode ser incluída no pacote EduGATE como um módulo suplementar.P. M. M. Correia is supported by the FCT (Lisbon) scholarship BD/52330/2013 under the PhD FCT program DAEPHYS, and is grateful to the I3N laboratory, funded by UID/CTM/50025/2013. This work was partially supported by project POCI-01-0145-FEDER-016855 and PTDC/BBB-IMG/4909/2014, and project easyPET nº 17823, through COMPETE, FEDER, POCI and FCT (Lisbon) programs.Programa Doutoral em Engenharia Civi

Investigation of microscale particles using a microfluidic flow cytometer equipped with a sensitive photodetector

We have developed a sensitive optofluidic cytometer to investigate microscale particles. The flow cytometer is comprised of a microchannel that has a set of chevron-shaped grooves. Conducted by the chevrons, two sheath streams focus the core stream in the center of the microchannel three-dimensionally. The optofluidic cytometer is equipped with the new generation of photodetectors, multi-pixel photon counter (MPPC). MPPCs are highly sensitive photodetectors with extremely small footprint that deliver high gain values of up to 107. We have employed a MPPC as the photodetector unit in our cytometer. Two different sizes of high intensity fluorescent microspheres are run through the cytometer. The signal outputs from both particles are collected using a data acquisition unit for further statistical analysis. The emission light produced by samples is received by a multimode fiber that is located in 135-degree with respect to the excitation fiber. The effect of particle size on the range of collected signal output is investigated by observing the forward scattering emission from samples. Statistical analysis of collected signal proved that for 10.2 µm particles, the peak height, width, and consequently area are larger than 3.2 µm particles. Finally using a 35 mW diode laser three types of algae are characterized in the flow cytometer based on their sizes. COMSOL software was employed to simulate the concentration distribution along the microchannel

A Low-Power Silicon-Photomultiplier Readout ASIC for the CALICE Analog Hadronic Calorimeter

The future e + e − collider experiments, such as the international linear collider, provide precise measurements of the heavy bosons and serve as excellent tests of the underlying fundamental physics. To reconstruct these bosons with an unprecedented resolution from their multi-jet final states, a detector system employing the particle flow approach has been proposed, requesting calorimeters with imaging capabilities. The analog hadron calorimeter based on the SiPM-on-tile technology is one of the highly granular candidates of the imaging calorimeters. To achieve the compactness, the silicon-photomultiplier (SiPM) readout electronics require a low-power monolithic solution. This thesis presents the design of such an application-specific integrated circuit (ASIC) for the charge and timing readout of the SiPMs. The ASIC provides precise charge measurement over a large dynamic range with auto-triggering and local zero-suppression functionalities. The charge and timing information are digitized using channel-wise analog-to-digital and time-to-digital converters, providing a fully integrated solution for the SiPM readout. Dedicated to the analog hadron calorimeter, the power-pulsing technique is applied to the full chip to meet the stringent power consumption requirement. This work also initializes the commissioning of the calorimeter layer with the use of the designed ASIC. An automatic calibration procedure has been developed to optimized the configuration settings for the chip. The new calorimeter base unit with the designed ASIC has been produced and its functionality has been tested