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1
Content available remote A review on the progress of ZnSe as inorganic scintillator
EN
Modern scintillator detectors act as an efficient tool for detection and measurement of ionizing radiations. ZnSe based materials have been found to be a promising candidate for scintillation applications. These scintillators show much-needed scintillation efficiency along with advantages such as high thermal and radiation stability, less-toxicity, non-hygroscopicity, emissions in the visible range and small decay time etc. Further, in quantum confinement regime, they show improvement in luminescent properties and size dependent emissions. In this review article, the attempt has been made to trace the progress of ZnSe based materials towards highly efficient quantum dot scintillators. Here, the fundamental process of scintillation has been explained. Factors such as doping, annealing, heavy ion irradiation which affects the scintillation response of ZnSe based scintillators have also been discussed. Method of synthesis plays a key role in optimization of quantum dot properties. Hence, it has been tried to trace the development in methods of synthesis of quantum dots. With optimized synthesis, we can extend applications of these highly efficient quantum dot scintillators for various scientific and industrial applications.
EN
Proper characterization of total electron content (TEC) and scintillation is very important to global positioning system (GPS) users in communication, navigation, ionospheric or atmospheric studies. Quiet time variation of TEC is useful in the estimation and removal of ionospheric delay for global navigation satellite systems single-frequency positioning. During geomagnetic storms, the variations of ionosphere deviate from their quiet day pattern and can cause significant effects on short-term prediction of various ionospheric parameters. The dynamics of the ionosphere change from region to region; therefore, in order to evaluate and improve the performance of global models of the ionosphere, numerous studies of variations using measured ionospheric parameters from stations globally are useful. This paper presents for the first time variations in the TEC and scintillation at Maseno University (geomagnetic coordinates, 9.64°S, 108.59°E), Kenya, investigated using a NovAtelGSV400B GPS receiver for the high solar activity year 2014. The GPS-measured TEC values were compared with the modeled TEC values by the latest International Reference Ionosphere model (IRI-2016), with a view to evaluate the performance of this version of the model. The largest TEC values were observed from 1300 to 1500 h local time throughout the year with the largest diurnal values occurring in March equinox and smallest during June solstice. The largest TEC values are attributed to extreme ultraviolet radiation coupled with upward →E ×→B plasma drift velocity. Nighttime enhancements in TEC attributed to the ‘fountain’ effect occurred during some months. Scintillation correlated with depletions in TEC occurred in the period between 1600 h local time to 1900 h local time (post-sunset) sector during some months, with the strongest value of − 0.91 being experienced in March equinox. Scintillation was absent during geomagnetic storms studied mainly as a result of the time of onset of the recovery phases of the storms. In addition, the geomagnetic storms were manifested in GPS-measured TEC as negative ionospheric storms. The IRI-2016 model gave a good prediction of measured values except for its overestimation of measured TEC in the months of May and June. Further, a new insight shown by the results is the ability of the IRI-2016 model to predict post-sunset TEC enhancements during some months contrary to previous versions reported by other researchers in East Africa. However, model is not quickly sensitive to transitions from one season to another. This result contributes to the improvement of the current IRI model by recommending the introduction of an input into the model that is sensitive to transitions in seasons in future versions of the model.
EN
A generalization of the Málaga atmospheric optical communications links treated as a finite number of generalized-K distributed sub-channels is analyzed in terms of outage probability and outage rate when its β parameter belongs to the set of real numbers. To the best of the author’s knowledge, this is the first time that β ∈ ℜ is considered. The new analytical expressions derived in this paper lead to a new physical and more realistic interpretation of atmospheric optical links, especially in terms of performance.
EN
Free Space Optical communication (FSO) has engrossed a large section of researchers in recent times due to its wide bandwidth, effortless deployment and immune links making it appropriate for communication purposes. This wireless optical technique requires clear and non-turbulent atmospheric conditions for efficient transmission. In this paper, authors aim at reducing the effect of turbulent atmospheric conditions like scintillation effect on FSO. Multibeam technique, which uses spatially diverse transmitters for transmission, has been used for increasing the achievable link distance of the FSO system. Parameters like quality factor and bit error rate have been used to check the received signal quality.
EN
A new and generalized statistical model, called Málaga distribution (M distribution), has been derived recently to characterize the irradiance fluctuations of an unbounded optical wave front propagating through a turbulent medium under all irradiance fluctuation conditions. As great advantages associated to that model, we can indicate that it is written in a simple tractable closed-form expression and that it is able to unify most of the proposed statistical models for free-space optical communications derived until now in the scientific literature. Based on that Málaga model, we have analyzed in this paper the role of the detection threshold in a free-space optical system employing an on-off keying modulation technique and involved in different scenarios, and taking into account the extinction ratio associated to the employed laser. First we have derived some analytical expressions for the lower-bound performance of the free-space optical system with the light intensity fading induced by turbulence obtained when the additive white Gaussian noise is not present in the system. Then, we have analyzed the optimal threshold in the system and how it changes when atmospheric conditions vary. Finally, a closed form expression for the bit error rate of that system is derived.
EN
Due to several complexities associated with the equatorial ionosphere, and the significant role which the total electron content (TEC) variability plays in GPS signal transmission, there is the need to monitor irregularities in TEC during storm events. The GPS SCINDA receiver data at Ile-Ife, Nigeria, was analysed with a view to characterizing the ionospheric response to geomagnetic storms on 9 March and 1 October 2012. Presently, positive storm effects, peaks in TEC which were associated with prompt penetration of electric fields and changes in neutral gas composition were observed for the storms. The maximum percentage deviation in TEC of about 120 and 45% were observed for 9 March and 1 October 2012, respectively. An obvious negative percentage TEC deviation subsequent to sudden storm commencement (SSC) was observed and besides a geomagnetic storm does not necessarily suggest a high scintillation intensity (S4) index. The present results show that magnetic storm events at low latitude regions may have an adverse effect on navigation and communication systems.
EN
The dual frequency SCINDA N ovAtel GSV 4004B GPS receiver installed at the Ile-Ife (low-latitude station) has been in operation since December 2009. Data records for the year 2010 were processed to obtain Total Electron Content (TEC) and S4 index. These were interpreted to analyze the ionospheric condition during low geomagnetic activity period (when Dst is from –40 to 0 nT) and during geomagnetic storm events (with Dst about –100 nT). Seasonal variations of the TEC and S4 index were also investigated. The occurrence of scintillations is closely linked to the peak value of TEC during the daytime; this is very evident during the equinox months when TEC ≥ 30 TECu. When the maximumTEC value is below 30 TECu, as shown by most of the days in the summer months, the scintillation phenomenon does not occur. During geomagnetic storms, the daytime segment of the TEC plot experiences fluctuations (even bifurcations) in values with the peak TEC value of about 40 TECu. From the interpreted data, the occurrence of geomagnetic storm does not necessarily suggest an increase in the level of scintillations at a low-latitude region. Also, there is a remarkable difference between the IRI 2007 model and the observed TEC values, as the daytime TEC peak differs in magnitude and time of occurrence from the ob served TEC.
EN
The conjugacy effects of the GPS scintillation activities during the geomagnetic storms of October 2003, November 2003 and July 2004 have been investigated at the approximately geomagnetically conjugate stations: Scott Base, Antarctica (SBA) and Resolute Cornwallis Island (RESO) in the high Arctic region. The measurements aim at investigation of the similarities and differences of the scintillation activities occurring at the conjugate points in the polar regions under storm conditions and examine the relationship between the Storm Enhanced Density (SED) and scintillation activity. The measurements of the scintillation activities obtained from total scintillation index during these storm periods at both hemispheres showed asymmetry in the ionospheric scintillation occurrence at the conjugate points. Pronounced scintillation activity was observed at the nightside hemisphere with the total scintillation index higher than at the dayside hemisphere. The results also show that the durations of severe scintillation activity were longer at the nightside hemisphere. The measurements showed that the intense scintillation periods were corresponding to the presence of the SED events where more pronounced SED events were observed over the nightside hemisphere.
PL
W artykule omówiony został fizyko–matematyczny model iskrzenia sprzęgła ciernego. Z procesem iskrzenia związana jest możliwość miejscowego podwyższenia temperatury i przekazywania energii, która może być przyczyną pożarów.
10
Content available remote Wzrost i właściwości scyntylacyjne monokryształów LuAlO3
PL
Opracowano nową technikę wzrostu kryształów LuAP metodą Czochralskiego, która umożliwia uzyskanie struktury perowskitu bez jakiejkolwiek domieszki szkodliwej dla scyntylacji fazy granatu. Zmierzone właściwości scyntylacyjne potwierdzają wysoką jakość optyczną uzyskanych krystałów, krótki czas zaniku impulsu scyntylacyjnego, oraz możliwość znacznego zwiększenia wydajności scyntylacji w porównaniu do opublikowanych wartości [2-6].
EN
New techniqe of growth of LuAP crystals by the Czochralski method has been worked out. The technique enable one to obtain perovskite structure without any garnet phase which is harmful for scintillating process. Measured scintillation properties confirm high optical quality of the obtained crystals, short decay constant of scintillating pulse, and possibility of large increase of light yield in comparison to published values [2-6].
EN
The method of the determination of radium isotopes (sup 226)Ra and (sup 228)Ra in the saline and mineral waters based on the LSC with the separation of α and β rays is presented. Concentrations of radium isotopes were calculated using Bateman equations for α and β components of (sup 226)Ra, (sup 228)Ra, without waiting for the radioactive equilibrium. The concentrations of these isotopes are very low in most mineral waters found in the market with the exception of two waters where the concentration of long life isotope (sup 226)Ra is high. Therefore, it is necessary to investigate the radium isotopes concentration in drinking mineral waters.
PL
Przedstawiono metodę oznaczania izotopów radu w zasolonych i mineralnych wodach, bazując na możliwości separacji widma alfa/beta na detektorze ciekłoscyntylacyjnym. Stężenia oznaczanych izotopów wyznaczano analitycznie, nie wyczekując osiągnięcia odpowiednich stanów równowagi promieniotwórczej. Analizę oparto na równaniach Batemana dla składowych alfa i beta (sup 226)Ra i (sup 228)Ra oraz odpowiednich procedurach obliczeniowych. Wykorzystując tę metodę przebadano wybrane, powszechnie dostępne wody mineralne, butelkowe. W większości wód stężenia tych izotopów są zdecydowanie niskie. Natomiast na szczególną uwagę zasługują wody z okolic Polanicy Zdroju, w których stężenie długożyciowego izotopu radu (sup 226)Ra jest wysokie (przy nieobecności izotopu (sup 228)Ra). Z punktu widzenia ochrony radiologicznej konieczne staje się badanie wód mineralnych na obecność izotopów radu.
12
Content available remote Comparison of two methods for (sup 226)Ra determination in mineral water
EN
(sup 226) Ra concentration in bottled mineral water has been determined by a liquid scintillation technique (LSC) with the separation of α from β pulses. Extraction of radon from 0.5 dm3 of water samples to 20 ml of a xylene based scintillation cocktail is sufficient for the determination of (sup 226)Ra concentrations above12 mBq/dm3 (with ±10% error). A lower (sup 226)Ra concentration (from 2.2 mBq/dm3) can be measured after preliminary co-precipitation of (sup 226)Ra with calcium phosphate at pH = 10 from 1.5 dm3 water samples. The obtained precipitates were dissolved with HCL solution directly in the scintillation vials and then the xylene based scintillation cocktail was added. The activity was measured after reaching a (sup 226)Ra - (sup 222)Rn equilibrium and the removal of water. Where as the (sup 226)Ra determination limit for the simple extraction method is not sufficient for some mineral water samples, the second more laborious method can be applied for (sup 226)Ra determination even in tap waters. From the examined mineral water available on the local market only in one case did the (sup 226)Ra activity exceed the limit of 100 mBq/dm3 for the total α activity in the bottled mineral waters.
PL
Stężenie (sup 226)Ra w butelkowanych wodach mineralnych oznaczano techniką ciekłej scyntylacji z separacją impulsów α od β. Prosta ekstrakcja równowagowego (sup 222)Rn z próbek wody o objętości 0.5 dm3 do 20 mi scyntylatora ksylenowego pozwala na oznaczanie poziomów (sup 226)Ra wyższych od 12 mBq/dm3 (z błędem ±10%). Niższe stężenia (>2.2 mBq/dm3) można mierzyć po wstępnym zatężeniu (sup 226Ra) przez współstrącanie z fosforanem wapnia z próbki wody o objętości 1.5 dm3 przy pH = 10. Otrzymany osad rozpuszczano w stężonym HCI bezpośrednio w naczynkach scyntylacyjnych. Następnie dodawano do nich 10 mi scyntylatora ksylenowego. Aktywność (sup 222)Rn i produktów jego rozpadu mierzono po ustaleniu się równowagi (sup 226)Ra - (sup 222)Rn i usunięciu warstwy wodnej. Metoda ta pozwala oznaczyć zawartość 226Ra również w wodach otwartych oraz w wodzie wodociągowej. Tylko w jednej wodzie mineralnej stwierdzono przekroczenie dopuszczalnego limitu całkowitej aktywności a wynoszącego 100 mBq/dm3.
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