1,721,011 research outputs found
Silicon Carbide Microstrip Radiation Detectors
Full text linkCompared with the most commonly used silicon and germanium, which need to work at cryogenic or low temperatures to decrease their noise levels, wide-bandgap compound semiconductors such as silicon carbide allow the operation of radiation detectors at room temperature, with high performance, and without the use of any bulky and expensive cooling equipment. In this work, we investigated the electrical and spectroscopic performance of an innovative position-sensitive semiconductor radiation detector in epitaxial 4H-SiC. The full depletion of the epitaxial layer (124 μm, 5.2 × 10^13 cm^-3) was reached by biasing the detector up to 600 V. For comparison, two different microstrip detectors were fully characterized from -20 °C to +107 °C. The obtained results show that our prototype detector is suitable for high resolution X-ray spectroscopy with imaging capability in a wide range of operating temperatures
Silicon Carbide Detector for Laser-Generated Plasma Radiation
No full textWe present the performance of a Silicon Carbide (SiC) detector in the acquisition of the radiation emitted by laser generated plasmas. The detector has been employed in time of flight (TOF) configuration within an experiment performed at the Prague Asterix Laser System (PALS). The detector is a 5 mm(2) area 100 nm thick circular Ni-SiC Schottky junction on a high purity 4H-SiC epitaxial layer 115 mu m thick. Current signals from the detector with amplitudes up to 1.6 A have been measured, achieving voltage signals over 80 V on a 50 Omega load resistance with excellent signal to noise ratios. Resolution of few nanoseconds has been experimentally demonstrated in TOF measurements. The detector has operated at 250 V DC bias under extreme operating conditions with no observable performance degradation
Advances in Silicon Carbide X-Ray Detectors
No full textThe latest advances in SiC X-ray detectors are presented: a pixel detector coupled to a custom ultra-low noise CMOS preamplifier has been characterized at room and high temperature. An equivalent noise energy (ENE) of 113 eV FWHM, corresponding to 6.1 electrons r.m.s., has been achieved with the detector/front- end system operating at 30 °C. A Fano factor of F = 0.10 has been estimated from the 55Fe spectrum. When the system is heated up to 100 °C, the measured ENE is 163 eV FWHM (8.9 electrons r.m.s.). It is determined that both at room and at high temperature the performance are fully limited by the noise of the front-end electronics. It is also presented the capability of SiC detectors to operate in environments under unstable temperature conditions without any apparatus for temperature stabilization; it has been proved that a SiC detector can acquire high resolution X-ray spectra without spectral line degradation while the system temperature changes between 30 °C and 75 °C.</p
Silicon Carbide Microstrip Detectors For High Resolution X-Ray Spectroscopy
No full textSilicon Carbide (SiC) is a wide bandgap semiconductor with outstanding physical properties for realizing ionizing radiation detectors. We present the manufacturing, electrical and spectroscopic characterization of a prototype SiC microstrip detector constituted by 32 strips, 2 mm long, 25 mu m wide with 55 mu m pitch. The detectors have been fabricated on 115 mu m thick undoped epitaxial 4H-SiC using Ni-SiC Schottky junctions. The measured leakage currents are below 5 fA at +25C and 0.6 pA at +107C with internal electric fields up to 30 kV/cm. X-ray spectra from Fe-55 and Am-241 with energy resolution of 224 eV FWHM and 249 eV FWHM (12-13.5 electrons r.m.s.) have been acquired at +20C and +80C, respectively
Silicon carbide detectors for in vivo dosimetry
Full text linkSemiconductor detectors for in vivo dosimetry haveserved in recent years as an important part of quality assurancefor radiotherapy. Silicon carbide (SiC) can represent a bettersemiconductor with respect to the more popular silicon (Si) thanksto its physical characteristics such as wide bandgap, high electronsaturation velocity, lower effective atomic number, and high radiationresistance to X and gamma rays. In this article we present aninvestigation aimed at characterizing 4H-SiC epitaxial Schottkydiodes as in vivo dosimeters. The electrical characterization atroom temperature showed ultra low leakage current densities aslow as 0.1 pA/cm at 100 V bias with negligible dependence ontemperature. The SiC diode was tested as radiotherapy dosimeterusing 6 MV photon beams from a linear accelerator in a typicalclinical setting. Collected charge as a function of exposed radiationdose were measured and compared to three standard commerciallyavailable silicon dosimeters. A sensitivity of 23 nC/Gy withlinearity errors within 0.5% and time stability of 0.6% wereachieved. No negligible effects on the diode I-V characteristicsafter irradiation were observed.</p
X-gamma Ray Spectroscopy With Semi-Insulating 4H-Silicon Carbide
No full textRadiation detectors on a semi-insulating (SI) 4H silicon carbide (SiC) wafer have been manufactured and characterized with X and γ photons in the range 8-59 keV. The detectors were 400-μm-diameter circular Ni-SiC junctions on an SI 4H-SiC wafer thinned to 70 μm. Dark current densities of 3.5 nA/cm2 at +20°C and 0.3 μA / cm2 at +104°C with an internal electric field of 7 kV/cm have been measured. X-γ ray spectra from 241Am have been acquired at room temperature with pulser line width of 756 eV FWHM. The charge collection efficiency (CCE) has been measured under different experimental conditions with a maximum CCE = 75% at room temperature. Polarization effects have been observed, and the dependence of CCE on time and temperature has been measured and analyzed. The charge trapping has been described by the Hecht model with a maximum total mean drift length of 107 μm at room temperature
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
Characterizing the Timing Performance of a Fast 4H-SiC Detector With an 241Am Source
No full textAn SPX4 4H-silicon carbide detector consisting of 4 x 4 pixels was developed and studied experimentally. Its pixel size is 400 μm x 400 μm . A timing resolution of 117 11 ps fullwidth at half-maximum (FWHM) has been measured for thedetection of alphas. With such good timing performance andhigh granularity, the SiC pixel detector holds great promise as anassociated alpha-particle detector for fast neutron imaging.</p
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
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