Scintillation

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

Spectroscopy and scintillation properties of cerium doped YAlO3 single crystals

Abstract: A study of the spectroscopic and scintillation properties of Ce doped YAlO3 single crystals is presented. The relation between the method of crystal growth, in vacuum or by the Czochralski method, and the above properties was studied specifically. Vacuum grown crystals show a scintillation light yield of about 14000 photons per megaelectronvolt of absorbed x-ray energy. It is concluded that cation vacancies present in the Czochralski grown crystals cause a decrease of the light yield. The influence of colour centres such as F and F- centres on the spectroscopic and scintillation properties will be discussed.

A Review of Ionospheric Scintillation Models

Abstract: This is a general review of the existing climatological models of ionospheric radio scintillation for high and equatorial latitudes. Trans-ionospheric communication of radio waves from transmitter to user is affected by the ionosphere which is highly variable and dynamic in both time and space. Scintillation is the term given to irregular amplitude and phase fluctuations of the received signals and related to the electron density irregularities in the ionosphere. Key sources of ionospheric irregularities are plasma instabilities; every irregularities model is based on the theory of radio wave propagation in random media. It is important to understand scintillation phenomena and the approach of different theories. Therefore, we have briefly discussed the theories that are used to interpret ionospheric scintillation data. The global morphology of ionospheric scintillation is also discussed briefly. The most important (in our opinion) analytical and physical models of scintillation are reviewed here.

Elastic scatter computed tomography

Abstract: A technique is proposed for imaging 2D sections based on measurement of elastic scatter radiation. In this new imaging method the radiation from a conventional X-ray source (Philips MCN 165 160 kVp tube operated at 140 kVp and 4.6 mA with 0.6 mm focus) is collimated by a lead diaphragm (1.0 mm) and falls on the object to be investigated. The transmitted radiation and the scatter falling within a range of half-angle 6 degrees (with reference to the object centre) are recorded by seven scintillation detectors (BGO) operated in current integration mode. Each scintillation crystal subtends an angular range of 1 degrees . The detector array comprises three scatter detectors arranged symmetrically on either side of the central transmission detector in such a way that six (partially overlapping) scatter measurements result.

Outage Probability of the Gaussian MIMO Free-Space Optical Channel with PPM

Abstract: The free-space optical channel has the potential to facilitate inexpensive, wireless communication with fiber-like bandwidth under short deployment timelines. However, atmospheric effects can significantly degrade the reliability of a free-space optical link. In particular, atmospheric turbulence causes random fluctuations in the irradiance of the received laser beam, commonly referred to as scintillation. The scintillation process is slow compared to the large data rates typical of optical transmission. As such, we adopt a quasi-static block fading model and study the outage probability of the channel under the assumption of orthogonal pulse-position modulation. We investigate the mitigation of scintillation through the use of multiple lasers and multiple apertures, thereby creating a multiple-input multiple output (MIMO) channel. Non-ideal photodetection is also assumed such that the combined shot noise and thermal noise are considered as signal-independent Additive Gaussian white noise. Assuming perfect receiver channel state information (CSI), we compute the signal-to-noise ratio exponents for the cases when the scintillation is lognormal, exponential and gamma-gamma distributed, which cover a wide range of atmospheric turbulence conditions. Furthermore, we illustrate very large gains, in some cases larger than 15 dB, when transmitter CSI is also available by adapting the transmitted electrical power.

Effect of eddy diffusivity ratio on underwater optical scintillation index.

Abstract: The performance of underwater optical wireless communication systems is severely affected by the turbulence that occurs due to the fluctuations in the index of refraction. Most previous studies assume a simplifying, yet inaccurate, assumption in the turbulence spectrum model that the eddy diffusivity ratio is equal to unity. It is, however, well known that the eddy diffusivities of temperature and salt are different from each other in most underwater environments. In this paper, we obtain a simplified spatial power spectrum model of turbulent fluctuations of the seawater refraction index as an explicit function of eddy diffusivity ratio. Using the derived model, we obtain the scintillation index of optical plane and spherical waves and investigate the effect of the eddy diffusivity ratio.