Scintillation

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

Amplitude and phase scintillation measurements on 8.2 km line-of-sight path at 30 GHz

Abstract: The letter summarises results of amplitude and phase scintillation measurements at 30 GHz on an 8.2 km line-of-sight path in the Netherlands. The measured results compare favourably with those obtained from weak-scattering theory.

The NANOGrav Nine-year Data Set: Monitoring Interstellar Scattering Delays

Abstract: We extract interstellar scintillation parameters for pulsars observed by the NANOGrav radio pulsar timing program. Dynamic spectra for the observing epochs of each pulsar were used to obtain estimates of scintillation timescales, scintillation bandwidths, and the corresponding scattering delays using a stretching algorithm to account for frequency-dependent scaling. We were able to measure scintillation bandwidths for 28 pulsars at 1500 MHz and 15 pulsars at 820 MHz. We examine scaling behavior for 17 pulsars and find indices ranging from $-0.7$ to $-3.6$. We were also able to measure scintillation timescales for six pulsars at 1500 MHz and seven pulsars at 820 MHz. There is fair agreement between our scattering delay measurements and electron-density model predictions for most pulsars, with some significant outliers likely resulting from frequency channel resolution limits outside of this range. We derive interstellar scattering-based transverse velocities assuming a scattering screen halfway between the pulsar and earth. We also calculate the location of the scattering screens assuming proper motion and interstellar scattering-derived transverse velocities are equal. We find no correlations between variations in scattering delay and either variations in dispersion measure or flux density. For most pulsars for which scattering delays were measurable, we find that time of arrival uncertainties for a given epoch are larger than our scattering delay measurements, indicating that variable scattering delays are currently subdominant in our overall noise budget but are important for achieving precisions of tens of ns or less.

The Use of Radio Stars to Study Irregular Refraction of Radio Waves in the Ionosphere

Abstract: The observations and the theory of radio star scintillation are reviewed, and the following conclusions are reached. 1) The frequency variation of amplitude and phase scintillations agrees with theory. 2) All observers agree that there is a marked increase of amplitude scintillation with increase in zenith angle. The Cambridge data agrees with theory, but the Manchester data does not. No available zenith angle data is adequate to determine the height of scintillation. 3) The available observations of phase scintillation are inadequate for almost all purposes. 4) At present, the Hewish method of locating height by comparing amplitude and phase scintillation is seriously hampered by lack of satisfactory observations. On existing data the method gives heights that are spread over a range of about five to one; all of these heights are above the E region and refer to nighttime scintillation. 5) All observers agree that there is a maximum of amplitude scintillation in the middle of the night. 6) In addition, Australian observers report a maximum of amplitude scintillation at midday. This is only weakly observed, if at all, in the northern hemisphere, where, however, observational conditions are different. 7) Australian observers report maxima of amplitude scintillation at the solstices and minima at the equinox, but observers in the northern hemisphere report little seasonal variation. 8) The rate of scintillation increases under magnetically disturbed conditions, due to increased drift velocity. 9) There is a good general correlation between the occurrence of radio star scintillation and spread F reflections.

Development of scintillation materials for PET scanners

Abstract: The growing demand on PET methodology for a variety of applications ranging from clinical use to fundamental studies triggers research and development of PET scanners providing better spatial resolution and sensitivity. These efforts are primarily focused on the development of advanced PET detector solutions and on the developments of new scintillation materials as well. However Lu containing scintillation materials introduced in the last century such as LSO, LYSO, LuAP, LuYAP crystals still remain the best PET species in spite of the recent developments of bright, fast but relatively low density lanthanum bromide scintillators. At the same time Lu based materials have several drawbacks which are high temperature of crystallization and relatively high cost compared to alkali-halide scintillation materials. Here we describe recent results in the development of new scintillation materials for PET application.

Large barium fluoride detectors

Abstract: Big BaF2 crystals of 1–2 1 volume and up to 15 cm thickness were investigated with respect to their application as gamma-ray detectors. In particular, we were interested in the light transmission in the UV region, and the energy and time resolution. We found that an energy resolution of ∼ 12% (662 keV) and a time resolution of ∼ 0.4 ns (60Co, 300 keV threshold) can be obtained simultaneously. For these features, BaF2 is superior to NaI or BGO in cases where good timing is essential. Gamma-rays and alpha particles can be clearly discriminated; as for the latter the fast component does not show up in the scintillation light.