Scintillation

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

Cesium hafnium chloride: A high light yield, non-hygroscopic cubic crystal scintillator for gamma spectroscopy

Abstract: We report on the scintillation properties of Cs2HfCl6 (cesium hafnium chloride or CHC) as an example of a little-known class of non-hygroscopic compounds having the generic cubic crystal structure of K2PtCl6. The crystals are easily growable from the melt using the Bridgman method with minimal precursor treatments or purification. CHC scintillation is centered at 400 nm, with a principal decay time of 4.37 μs and a light yield of up to 54 000 photons/MeV when measured using a silicon CCD photodetector. The light yield is the highest ever reported for an undoped crystal, and CHC also exhibits excellent light yield nonproportionality. These desirable properties allowed us to build and test CHC gamma-ray spectrometers providing energy resolution of 3.3% at 662 keV.

Turbulence in the ionosphere with applications to meteor‐trails, radio‐star scintillation, auroral radar echoes, and other phenomena

Abstract: The irregularities in electron-density responsible for incoherent scattering of radio waves in the ionosphere are discussed on the assumption of isotropic turbulence in the neutral molecules, with allowance made for the effect of the earth's magnetic field on the associated irregularities in the density of the charges particles. The atmospheric model used is based on rocket observations, extrapolated upwards in height where necessary. Tentative formulas are deduced for the large eddies based on a non-standard application of the Richardson number. For the small eddies, the standard formulas of turbulence-theory are used. These formulas all depend on a quantity w, which is the rate of supply of turbulence-energy to the large eddies and also the rate of removal of turbulence-energy from the small eddies, measured per unit mass of atmosphere. The value of w at the meteoric level (90 km) is found to be around 25 watts/kg by comparison between the theory and meteoric observations (both visual and radio). By the same technique, a more tentative value of 1,000 watts/kg is deduced for the level responsible for scintillation of radio stars, although a lower value is probably appropriate when scintillation is weak. These values of w in the ionosphere are high compared with Brunt's value of 5×10−4 watt/kg for the troposphere. It is shown, however, that these high values of w in the ionosphere are quite possible and even reasonable. It is deduced that the time of onset of irregular fading of meteoric echoes in the VHF band is more likely to be due to roughness of the trail caused by the small eddies than to gross distortion of the trail caused by the large eddies. It follows that, after about a second, VHF radar echoes from a meteor-trail must be calculated using a theory based on incoherent scattering, thereby questioning the theory of Kaiser and Closs [37] as an explanation of long-duration meteor-echoes. It is also shown that radio-star scintillation cannot be explained in terms of turbulence at a level of 400 km, but that reasonable results can be obtained if the level is reduced to 200–300 km. Among other applications considered is the possibility of radio communication via incoherent scattering in the F region of the atmosphere. The conditions under which such communication should be sought are described in section 11.

Scintillation model for a satellite communication link at large zenith angles

Abstract: A scintillation model is developed for uplink-downlink optical communication channels applicable in moderate to strong fluctuation conditions that may arise under large zenith angles between transmitter and receiver. The model developed here is an extension of a recently published theory that treats irradiance fluctuations along a horizontal path as a modulation of small-scale scintillation by large-scale scintilla- tion. For a downlink path the scintillation index is modeled like that of an infinite plane wave, and for an uplink path we consider a spherical wave model. In both cases the scintillation index agrees with conventional weak-fluctuation-theory results out to zenith angles of 45 to 60 deg. The covariance function of irradiance fluctuations is also developed under the same conditions as assumed for the scintillation index. On a downlink path under small zenith angles the implied correlation length is propor- tional to the Fresnel-zone scale. For zenith angles exceeding 85 deg, the downlink correlation length varies directly with the spatial coherence ra- dius weighted by a factor that depends on changes in C n the refractive index structural parameter with altitude. © 2000 Society of Photo-Optical Instru- mentation Engineers. (S0091-3286(00)02412-0)

Scintillation Properties of and Self Absorption in ${\rm SrI}_{2}\!:\!{\rm Eu}^{2+}$

Abstract: The scintillation properties of pure SrI2 and SrI2 doped with 0.5%, 0.86%, 2%, and 5% europium were studied. Different techniques were used to measure γ-ray excited pulse-height and scintillation decay time spectra, and to perform X-ray excited and optically excited emission spectroscopy. Eu2+ emission and trapped exciton (TE) emission was observed in SrI2:Eu2+ samples. These emissions were studied as a function of temperature, Eu concentration, and sample size. A spectral overlap was observed between Eu2+ excitation and emission spectra, the amount of overlap depends on temperature. The light yield, energy resolution and luminescence decay profiles reveal also a dependence on temperature, sample size, and Eu concentration. The observations were analyzed and interpreted in terms of two separate models. One model consists of the relation between TE and Eu2+ emission and the other deals with self absorption processes.

Laser Scintillation Measurements of the Temperature Spectrum in the Atmospheric Surface Layer.

Abstract: The locally stationary temperature spectrum in the atmospheric surface layer is estimated using laser scintillation. The fluctuations of the parameters of the turbulence spectrum (the structure constant CT2 and inner scale l0) have a lognormal distribution. The average spectrum is calculated by averaging the locally stationary spectrum over these fluctuations. The average spectrum does not have a universal form. The fluctuations in the turbulence parameters produces a bias in measurements of the Obukhov-Corrsin constant and in estimates of energy dissipation rate ϵ based on average scintillation statistics. The performance of the scintillation technique and the accuracy of scintillation measurements of inner scale and structure constant are estimated using Monte Carlo simulation. One scintillation measurement can provide accurate estimates of the important turbulence parameters and the statistics of the fluctuations of these parameters. The scintillation estimates are true path-averaging estimate...