1,721,687 research outputs found
Measurement of charge collection efficiency profiles of CMOS active pixel sensors
No full textRecently, CMOS Active Pixels Sensors (APS) have become strong candidates as pixel detectors to be used in high energy physics experiments. A very good resolution and an excellent detection efficiency could be obtained with these detectors. In this paper we have experimentally studied, by means of charged particle beams at a grazing angle, for four different CMOS APS the diffusion properties of electron/hole pairs formed by ionizing particles interacting within the sensitive silicon layer beneath the sensor surface. By averaging many events originating at the same distance from the surface of the device, we extracted with great accuracy the charge collection efficiency (CCE) profiles of the four sensors under test. Basic transport parameters (minority carrier diffusion length, minority carrier lifetime, width of the region at maximum CCE) have been extracted using a mathematical procedure based on the extended Ramo's theorem
A laser test system for characterizing CMOS active pixel sensors
No full textCMOS active pixel sensor suitability for radiation detection purposes has been already demonstrated. In particular, the adoption of a
fully standard deep sub-micron CMOS technology allows to obtain a very compact pixel size, an efficient integration of smart electronics
and ease of porting to future, more advanced, technology nodes. These characteristics potentially enhance the sensor capabilities, in
terms of spatial resolution and energy resolution. In order to verify such hypotheses, test chips have been fabricated, and a dedicated
laser test bench has been devised and implemented. The test bench features a mechanical movement section with sub-micron positioning
capabilities, and an optic axis with a beam-splitter that allows the fine focalization of a near infrared laser stimulus and also to obtain a
visible picture to control the irradiated region. A low-cost comprehensive active pixel sensor characterization can be therefore carried out
as an alternative to more expensive beam test characterizations
Vertically integrated CMOS active pixel sensors for tracking applications in HEP experiments
No full textn this work we propose an innovative approach to particle tracking based on CMOS Active Pixel Sensors layers, monolithically integrated in an all-in-one chip featuring multiple, stacked, fully functional detector layers capable to provide momentum measurements (particle impact point and direction) within a single detector. This will results in a very low material detector, thus dramatically reducing multiple scattering issues. A first chip prototype has been fabricated within a multi-project run using a 130nm CMOS 3D Chartered/Tezzaron technology, featuring two layers bonded face-to-face. Tests have been carried out on full 3D structures, providing the functionalities of both tiers and their inter-communications. Actually, laser scans have been carried out using highly focussed spot size, obtaining coincidence responses of the two layers. X-rays sources have been used as well for sensor calibration purposes. Beam tests with 3MeV protons have been carried out at the INFN LABEC laboratories in Florence (Italy) to assess the suitability of the proposed approach for Minimum Ionizing Particle detection
Characterization of CMOS Active Pixel Sensors for particle detection: Beam test of the four-sensors RAPS03 stacked system
No full textRAPID: A prototype for personnel dosimetry during interventional radiology procedures
No full textPurpose: We present the tests performed on the prototype of a personal wireless dosimeter for medical staff during Interventional Radiology procedures, developed in the framework of the INFN RAPID Project.
Methods and materials: The prototype is composed by a sensing element (a CMOS silicon pixel device), a real-time data reduction system (a CPLD), a control system, a wireless transmission module, a remote station for prototype configuration, control and data storage.
The prototype has been irradiated in laboratory using monochromatic X-ray photons to calibrate the sensing element, then using the angiography system with a PMMA phantom, to diffuse the direct radiation, in all the working conditions (continuous/pulsed, fluoroscopy/digital radiography acquisition) and with different sensor settings. The prototype has also been exposed to a certified X-ray beam to obtain a relative calibration. Finally the sensing element of the prototype has also been used during medical procedures, mounted over the lead apron dressed by the medical staff.
All the results have been compared with two control systems, a set of TLDs and an UNFORS EDD-30 system.
Results: Two sensor quantities have been used to verify the linearity of the prototype's response:
the number of detected photons and the total detected signal in a frame. The appropriate data reduction strategies have then been implemented in CPLD to obtain a limited amount of data to be transmitted to the remote station with a 1-10 Hz frequency, lowering the needed throughput of the wireless system, and hence the power consumption.
The uncertainty on the dose and dose-rate measurements is below 10%, and the wireless transmission protocol has been found to be adequate also in the capability of establishing the connection through the operating room walls.
Conclusion: The wireless dosimeter prototype, produced in the framework of the RAPID project, for personnel dosimetry of the medical staff during interventional radiology procedures, has been tested and found to be satisfactory from the power consumption, the wireless transmission capability, the precision in dose and dose-rate measurements
Direct detection of high intensity X-ray fluxes with silicon photomultipliers
No full textSilicon Photomultipliers (SiPM) are photodetectors optimized for the detection of infrared to ultraviolet photons and employed in a wide range of fast timing applications for medical imaging and particle detectors. SiPMs are used to detect the passage of ionizing radiation into matter via the collection of secondary photons emitted by the radiator material. In this work, we have investigated the possibility to detect high intensity X-ray fluxes using the DC current produced by SiPMs exposed directly to the X-ray beam, in absence of any passive converter material, to demonstrate the possibility to measure intense radiation fluxes without saturation of the SiPM response. In our application, the signal-to-noise ratio of the SiPM current during the direct exposition to X-rays is typically larger than 100, providing a robust indication of a positive detection. We show that, for a wide range of operational parameters and X-ray flux intensities, the SiPM current can be correlated to the X-ray beam intensity using a parametrization that describes the data with an accuracy of the order or better than 1%. We also show that the SiPM signal current to dark current ratio is maximum for hundreds of mV above the breakdown voltage, with a weak dependence on temperature. These results open the prospects for interesting applications for monitoring intense X-ray beams, for example beam spatial profiling, and possibly real time dosimetry both in medical and industrial applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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