115,624 research outputs found
Superconducting Strips: A Concept in Thermal Neutron Detection
No full textIn the never-ending quest for better detection efficiency and spatial resolution, various thermal neutron detection schemes have been proposed over the years. Given the presence of some converting layers (typically boron, but 6LiF is also widely used nowadays), the shift towards concepts based on solid state detectors has been steadily increasing and ingenious schemes thereby proposed. However, a trade-off has been always sought for between efficiency and spatial resolution; the problem can be (at least partially) circumvented using more elaborate geometries, but this complicates the sample preparation and detector construction. Thus, viable alternatives must be found. What we proposed (and verified experimentally) is a detection scheme based on the superconducting to normal transition. More precisely, using a boron converting layer, the α particles (generated in the (n, α) reaction) crossing a low critical temperature superconducting strip some 10 µm wide have been detected; the process, bolometric in nature and based on the ionization energy loss, is intrinsically fast and the spatial resolution very appealing. In this work, some of the work done so far will be illustrated, together with the principles of the measurement and various related problems. The realization of the detector is based on industrial deposition and photolitographic techniques well within the grasp of a condensed matter laboratory, so that there is substantial room for improvement over our elementary strip geometry. Some of the plans for future work will also be presented, together with some improvements both in the choice of the materials and the geometry of the detector
Rivelatore a film sottile superconduttore per neutroni termici
No full textSi propone lo schema di principio per la realizzazione di un sistema di rivelazione di neutroni termici costituito da un multistrato superconduttore-Boro (in composizione naturale o isotopica 10B) depositato su substrato di Silicio-Ossido di Silicio. I neutroni termici vengono assorbiti nel Boro attraverso una reazione nucleare (cattura) che genera come prodotti particelle cariche; queste perdendo energia per ionizzazione generano un impulso di tensione nel film sottile superconduttore polarizzato in corrente permettendo quindi la rivelazione indiretta del passaggio dei neutroni.
Per la rivelazione è essenziale che il multistrato abbia una forma di rettangolo lungo e stretto, con dimensioni tipiche: lunghezza L= 1 mm, larghezza W= 10-20 micrometri;
lo spessore puo’ essere scelto grande a piacere, compatibilmente con le difficoltà di depositare film sottili con buone caratteristiche di omogeneità ed aderenza. Qui si propone uno spessore totale tra 0.6-1.0 micrometri (0.15-0.3 micrometri per il superconduttore, 0.45-0.7 micrometri per il Boro).
E’ importante notare che la ridotta dimensione trasversale, essenziale per una buona efficienza di rivelazione dei prodotti carichi, costituisce un ulteriore merito della configurazione poiché permette una elevata risoluzione spaziale. Inoltre, a partire da questa configurazione si possono concepire geometrie planari a pettine e a maglia, anche a strati eventualmente sovrapposti.A new system for the detection of thermal neutrons is proposed, composed by a supeconductor- Boron (either natural or 10B isotope) multilayer deposited on a Silicon-Silicon Oxide substrate.
Thermal neutrons are absorbed in Boron through a capture nuclear reaction which generates charged products; the latter, via energy loss by ionization, cause a voltage drop in the current-polarized superconducting thin film, thus allowing the indirect recording of the neutron event.
To allow for proper detection, it is of paramount importance that the multilayer is in the shape of a long narrow strip, with in-plane typical dimensions: length L=1 mm or longer, width w=10 to 20 micrometers; the thickness can be chosen at will, limited by the capability of growing thin films with good properties in terms of homogeneity and adhesion. Here a total thickness of 0.6 to 1.0 micrometers (0.15 to 0.3 for the superconducting film, 0.45 to 0.7 micrometers for Boron) is proposed.
It is well worth noticing that the reduced lateral dimension, important for a good overall efficiency of the detection process, is a further bonus since it allows a high spatial resolution.
Furthermore, starting from this basic configuration, planar comb-like or mesh geometries can be conceived, possibly with overlapping layers
Descriptive analysis and evaluation of the components of the quarter
No full textCapitolo che si riferisce all’individuazione dei nodi, dei percorsi, dei riferimenti, dei margini (con riferimento ai principi introdotti da K. Lynch), del quartiere Greco- Ortodosso dell'Annunciazione a Nazareth (Is) e alla loro valutazione secondo gli indicatori di qualità/degrado, livello di conoscenza a scala locale, nazionale e mondiale, livello di accessibilità, livello di visibilità e livello di leggibilità (ispirandosi ai principi del Codice dei Beni Culturali italiano -D.Lgs. 42/2004).
In questa fase si è proceduto anche al rilievo ed alla restituzione grafica (L. Astegno), al rilievo dello stato di degrado (L. Astegno, M. Merlo) e alla lettura iconografica delle opere interne (M. Boscolo Marchi) della settecentesca Chiesa Ortodossa dell’Annunciazione che contiene, secondo la tradizione, il Pozzo di Maria
Particles, waves, and chaos in a driven nonlinear system
No full textWe present evidence that the autonomous sine-Gordon system, subject to time-independent boundary conditions, gives rise to two fundamental families of stable dynamical configurations : particle (soliton) excitations and linear mode-like oscillations. The two dynamical configurations are clearly separated by a threshold value of a boundary parameter. The competition between these two basic dynamic families gives rise to chaotic motion of solitons and unstable oscillatory patterns for a threshold value of a boundary parameter
Micro-opto-fluidic platform for solvents identification based on absorption properties in the NIR region
No full textSpectral detection of light transmission through capillaries filled with a fluid sample is a powerful solution for evaluating its composition. In this work, we present an optical method to distinguish water and alcohol samples in a rectangular glass micro-capillary, coupled to an external fluidic path and laid flat onto an aluminum bulk mirror, from the spectral transmittance in the near-infra-red (NIR) wavelength range 1.15–1.65 μm, which becomes sample-specific thanks to the contribution given by the spectral absorption properties of the fluid. The readout beam of broadband radiation is shone on the upper flat side of the micro-capillary with an incidence angle of 14°, crosses the glass walls and the channel depth twice, since it is reflected by the mirror, and it is then coupled to the monochromator input of an optical spectrum analyzer. The theoretical transmission spectra of the capillary filled just with air as well as with distilled water, isopropanol, ethylene glycol, and 95% ethanol (with 5% water content) are derived using analytical equations including the wavelength-dependent attenuation due to fluid absorption. Experimental results relative to the wavelength dependence of the ratio between the spectral transmittance in the presence of the fluid sample and of just air are found to be in agreement with the calculated theoretical behavior. [Figure not available: see fulltext.
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