Scintillation

About: Scintillation is a research topic. Over the lifetime, 14022 publications have been published within this topic receiving 187694 citations.

Properties of CsI(TI) — Renaissance of an old scintillation material

Abstract: CsI(TI) is an interesting material for calorimeters in high energy physics. Properties of this material are reported.

Bipolar climatology of GPS ionospheric scintillation at solar minimum

Abstract: [1] High-rate sampling data of Global Navigation Satellite Systems ionospheric scintillation acquired by a network of GPS Ionospheric Scintillation and TEC Monitor receivers located in the Svalbard Islands, in Norway and in Antarctica have been analyzed. The aim is to describe the “scintillation climatology” of the high-latitude ionosphere over both the poles under quiet conditions of the near-Earth environment. For climatology we mean to assess the general recurrent features of the ionospheric irregularities dynamics and temporal evolution on long data series, trying to catch eventual correspondences with scintillation occurrence. In spite of the fact that the sites are not geomagnetically conjugate, long series of data recorded by the same kind of receivers provide a rare opportunity to draw a picture of the ionospheric features characterizing the scintillation conditions over high latitudes. The method adopted is the Ground Based Scintillation Climatology, which produces maps of scintillation occurrence and of total electron content relative variation to investigate ionospheric scintillations scenario in terms of geomagnetic and geographic coordinates, interplanetary magnetic field conditions and seasonal variability. By means of such a novel and original description of the ionospheric irregularities, our work provides insights to speculate on the cause-effect mechanisms producing scintillations, suggesting the roles of the high-latitude ionospheric trough, of the auroral boundaries and of the polar cap ionosphere in hosting those irregularities causing scintillations over both the hemispheres at high latitude. The method can constitute a first step toward the development of new algorithms to forecast the scintillations during space weather events.

Eu2+-doped Ba2CsI5, a new high-performance scintillator

Abstract: The crystal growth and scintillation properties of Ba 2 CsI 5 :Eu 2+ are reported. Crystals were produced by the vertical Bridgman technique in a sealed quartz ampoule. Ba 2 CsI 5 :Eu 2+ presents excellent scintillation properties. An estimated light yield of 97,000±5,000 photons per MeV (ph/MeV) of absorbed gamma-ray energy was measured. An energy resolution (FWHM over peak position) of 3.8±0.3% was observed for the 662 keV full absorption peak. Pulsed X-ray luminescence measurements show a relatively complex time response with four exponential decay components of 48,383, 1500 and 9900 ns with a contribution to the total light output of 1%, 26%, 68% and 25%, respectively. Under X-ray and UV excitation, the emission corresponds to a broadband centered at 2.85 eV. First principles calculations show strong localization of the excited state on the Eu site. Ba 2 CsI 5 :Eu 2+ has a density of about 5 g/cm 3 . These first reported scintillation properties make Ba 2 CsI 5 :Eu 2+ a very high-performance scintillator.

Model of equatorial scintillations from in-situ measurements

Abstract: In-situ measurements of F-region irregularity amplitude and ambient electron density made by the retarding potential analyzer on OGO-6 near the perigee altitude of 400 km have been utilized to derive the variation of electron density deviation over the equatorial region. Based on these measured electron density deviations and other assumed model parameters including a three-dimensional power law form of irregularity spectrum with index 4, a model of equatorial scintillations is developed in the framework of diffraction theory. The percentage occurrence contours of estimated equatorial scintillations ≥ 4.5 dB at 140 MHz during 1900–2300 LMT for the period November–December 1969 and 1970 have been derived. The model is found to depict a pronounced longitude variation with the scintillation belt width and percentage occurrence being maximum over the African sector. The latitude extent of the spatial scintillation belt narrows over the American sector without much decrease in the scintillation occurrence whereas over the Indian and Far Eastern sectors both the extent and the occurrence are found to decrease. The percentage occurrence of scintillations estimated from this model is found to be consistent with VHF scintillation measurements at Ghana, Huancayo, and Calcutta. In addition, the model was found to be in qualitative agreement with GHz observations at various longitudes made by the COMSAT group. The effects of varying model parameters on scintillation estimates at VHF, UHF, and GHz are discussed. Implications of the observed longitudinal variation of scintillations on current theories of equatorial irregularity formation are indicated.

Rapid Variability and Annual Cycles in the Characteristic Time-scale of the Scintillating Source PKS 1257-326

Abstract: Rapid radio intra-day variability (IDV) has been discovered in the southern quasar PKS 1257-326. Flux density changes of up to 40% in as little as 45 minutes have been observed in this source, making it, along with PKS 0405-385 and J1819+3845, one of the three most rapid IDV sources known. We have monitored the IDV in this source with the Australia Telescope Compact Array (ATCA) at 4.8 and 8.6 GHz over the course of the last year, and find a clear annual cycle in the characteristic time-scale of variability. This annual cycle demonstrates unequivocally that interstellar scintillation is the cause of the rapid IDV at radio wavelengths observed in this source. We use the observed annual cycle to constrain the velocity of the scattering material, and the angular size of the scintillating component of PKS 1257-326. We observe a time delay, which also shows an annual cycle, between the similar variability patterns at the two frequencies. We suggest that this is caused by a small (~10 microarcsecond) offset between the centroids of the 4.8 and 8.6 GHz components, and may be due to opacity effects in the source. The statistical properties of the observed scintillation thus enable us to resolve source structure on a scale of ~10 microarcseconds, resolution orders of magnitude higher than current VLBI techniques allow. General implications of scintillation for the physical properties of sources and the turbulent ISM are discussed.