127 research outputs found
Scintillation, phonon and defect channel balance, the sources for fundamental yield increase
The estimation of the fundamental limits of scintillation efficiency requires the analysis not only of electron channel of the energy transformation but also of the role of interplay between electron and phonon channels. The well-known factor beta which estimates the efficiency of electron-hole pair production is determined by the balance of these channels at the cascade and thermalization stages. The attention is paid to phonon production and relaxation at different stages of energy transformation in scintillators, starting from linear processes of emission of bulk phonons to multiphonon processes resulting in the production of local phonons and transient defect creation. The analysis shows that transient defects can play some positive role, being the centers of exciton stabilization. The spatial and temporal evolution of phonon subsystem and its interaction with electron subsystem in scintillators is analyzed. The role of phonons in the regions of high density of excitations (final region of tracks of primary and delta-electrons) is underlined. Possible experiments with simultaneous detection of these two channels are discussed
Electronics Thermal Management in Information and Communications Technologies: Challenges and Future Directions
This paper reviews thermal management challenges encountered in a wide range of electronics cooling applications from large-scale (data center and telecommunication) to smallscale systems (personal, portable/wearable, and automotive). This paper identifies drivers for progress and immediate and future challenges based on discussions at the 3rd Workshop on Thermal Management in Telecommunication Systems and Data Centers held in Redwood City, CA, USA, on November 4–5, 2015. Participants in this workshop represented industry and academia, with backgrounds ranging from data center thermal management and energy efficiency to high-performance computing and liquid cooling, thermal management in wearable and mobile devices, and acoustic noise management. By considering a wide range of electronics cooling applications with different lengths and time scales, this paper identifies both common themes and diverging views in the thermal management community
Altitude profile of aerosols on Mars from measurements of its thermal radiation on limb
Measurements of the thermal (range 7 - 13 micrometers) radiation of Mars with the high space resolution (approximately 2 km) were made by the TERMOSKAN experiment of the Phobos mission. Some of the results were published earlier but only the surface radiation was analyzed in detail. However some part of these measurements was made near the limb of the planet. The atmosphere gives an important input here in the planetary thermal radiation. Beyond the limb the atmosphere is the only source. The task of this work is to estimate some characteristics of the atmosphere using brightness profiles of the thermal radiation near the limb. An appropriate model of the temperature profile T(h) is necessary for such an analysis. A set of T(h) models (nominal, maximal and minimal) was defined using various sources including MARSGRAM, Viking-1 lander data, its theoretical considerations and boundary layer models. On the next step the possible input of the atmospheric gaseous emissions (wing of CO2 15 micrometer band) was estimated. It was found that even for the maximal T(h) this input is no more than a few percents of the measured radiation beyond the limb. Consequently the aerosols are responsible for almost all measured emission. The analysis of the observed profile showed that these aerosols have two components: (1) exponential with the scale height about 10 km and (2) some layered structure (two layers with maxima about 23 and 33 km consisted probably of ice)
Radioactive contamination of SrI2(Eu) crystal scintillator
A strontium iodide crystal doped by europium (SrI2(Eu)) was produced by using
the Stockbarger growth technique. The crystal was subjected to a
characterization that includes relative photoelectron output and energy
resolution for gamma quanta. The intrinsic radioactivity of the SrI2(Eu)
crystal scintillator was tested both by using it as scintillator at sea level
and by ultra-low background HPGe gamma spectrometry deep underground. The
response of the SrI2(Eu) detector to alpha particles (alpha/beta ratio and
pulse shape) was estimated by analysing the 226Ra internal trace contamination
of the crystal. We have measured: alpha/beta=0.55 at E_alpha=7.7 MeV, and no
difference in the time decay of the scintillation pulses induced by alpha
particles and gamma quanta. The application of the obtained results in the
search for the double electron capture and electron capture with positron
emission in 84Sr has been investigated at a level of sensitivity: T_1/2 \sim
10^{15}-10^{16} yr. The results of these studies demonstrate the potentiality
of this material for a variety of scintillation applications, including
low-level counting experiments.Comment: 24 pages, 12 figures, 4 tables, accepted for publication on Nucl.
Instrum. Meth.
Inter-calibration of Infrared Channels of Geostationary Meteorological Satellite Imagers
This article examines a method of inter-calibration for MSU-GS imager of the Russian Geostationary Earth Orbit (GEO) satellite Elektro-L No. 2. Since the launch (December 11, 2015), the satellite's radiation cooler has been operating in an abnormal mode, so the calibration of the IR channels of the MSU-GS imager differed from that pre-flight and, in general, could have a daily variability. To ensure the satellite's further operation in orbit, it was necessary to calibrate imager channels at a frequency that would allow to identify daily calibration course to detect and compensate its sources. In order to do this, we have developed a special method of GEO-GEO inter-calibration. The calibration of MSU-GS was performed using SEVIRI imager installed on the GEO satellite Meteosat-10. SEVIRI was chosen as a reference instrument because its spectral channels are similar to those of MSU-GS. The MSU-GS was calibrated according to the regressions calculated from the simultaneous images of the field of regard selected between the sub-satellite points. The dynamic brightness temperature range was determined by deep convective clouds in high troposphere and warm ocean surface. Using the proposed method of inter-calibration, it was possible to confirm the absence of a significant daily variation of the calibration since November 2017. The amplitude of the variation smoothly increases from ~0.2 K at high (~300 K) BTs to ~1.0 K when the brightness temperature decreased to 200 K. These estimates allow the use of the Fourier spectrometer IKFS-2 installed on the Russian Low-Earth-Orbit (LEO) satellite Meteor-M No. 2 to verify the developed GEO-GEO scheme of inter-calibration. Despite the specifics of the situation on board Elektro-L No. 2, the proposed method of GEO-GEO inter-calibration can be applied to radiometers of other neighboring satellites that differ in SSP and spatial resolution
Solder joint failures under thermo-mechanical loading conditions – a review
Solder joints play a critical role in electronic devices by providing electrical, mechanical and thermal interconnections. These miniature joints are also the weakest links in an electronic device. Under severe thermal and mechanical loadings, solder joints could fail in ‘tensile fracture’ due to stress overloading, ‘fatigue failure’ because of the application of cyclical stress and ‘creep failure’ due to a permanent long-term load. This paper reviews the literature on solder joint failures under thermo-mechanical loading conditions, with a particular emphasis on fatigue and creep failures. Literature reviews mainly focused on commonly used lead-free Sn-Ag-Cu (SAC) solders. Based on the literature in experimental and simulation studies on solder joints, it was found that fatigue failures are widely induced by accelerated thermal cycling (ATC). During ATC, the mismatch in coefficients of thermal expansion (CTE) between different elements of electronics assembly contributes significantly to induce thermal stresses on solder joints. The fatigue life of solder joints is predicted based on phenomenological fatigue models that utilise materials properties as inputs. A comparative study of 14 different fatigue life prediction models is presented with their relative advantages, scope and limitations. Creep failures in solder joints, on the other hand, are commonly induced through isothermal ageing. A critical review of various creep models is presented. Many of these strain rate-based creep models are routed to a very well-known Anand Model of inelastic strain rate. Finally, the paper outlined the combined effect of creep and fatigue on solder joint failure.N/
Radiation damage of CsI:Eu crystals
The problems of radiation damage and afterglow nature for CsI:Eu crystal are discussed. It was determined that the luminescence parameters depend on the X-ray irradiation conditions. Irradiation leads to emission suppression at doses less than 100 Gy when the induced absorption was not observed yet. Hole (VF⁻ and I₃⁻) and activator′ color centers formation lead to partial decrease of the intrinsic UV and the activator luminescence, but it is not the dominating process of the radiation-induced phenomenon. The reverse dependences of afterglow and Eu²⁺ luminescence on irradiation dose were detected. Radiation induced luminescence quenching is determined by a modification of the activator centers structure
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