Search results for " attenuation"

Determination of mass attenuation coefficient by numerical absorption calibration with Monte-Carlo simulations at 59.54 keV

2016

Abstract This study presents a numerical method in order to determine the mass attenuation coefficient of a sample with an unknown chemical composition at low energy. It is compared with two experimental methods: a graphic method and a transmission method. The method proposes to realise a numerical absorption calibration curve to process experimental results. Demineralised water with known mass attenuation coefficient ( 0.2066 cm 2 g − 1 at 59.54 keV) is chosen to confirm the method. 0.1964 ± 0.0350 cm 2 g − 1 is the average value determined by the numerical method, that is to say less than 5% relative deviation compared to more than 47% for the experimental methods.

Raman based distributed fiber optic temperature sensors for structural health monitoring in radiation environment

2015

Raman distributed temperature sensor (RDTS) measurements were performed during γ-radiation on three different classes of standard multimode fibers (pure, Ge-doped and F-doped). The sensor response is affected by the radiation induced attenuation phenomena leading to errors in the temperature measurements. The amplitude of this error strongly depends on the fiber type and the irradiation conditions. These results are promising in view of the integration of these RDTS into the deep geological repository for radioactive waste.

Measured and predicted light attenuation in dense coastal upslope fog at 650, 850, and <inline-formula><math display="inline" overflow="scro…

2008

Free-space optics FSO has gained considerable importance in this decade of demand for high-bandwidth transmission capabilities. FSO can provide the last mile solution, but the availability and reliability issues concerned with it have received increasing attention and need thorough investigation. In this work, we present our results on fog attenu- ation measurement and prediction at wavelengths 650, 850, and 950 nm with peak values up to 500 dB/km. For the attenuation measurement, optical wavelengths are transmitted over the same path of fog in free air to a receiver, measuring the power at every wavelength. The measure- ment of fog attenuation was performed at the France Telecom RD free-sp…

ARCADE: Description of the project and setup of the Lidar/AMT system

2015

The ARCADE (Atmospheric Research for Climate and Astroparticle DEtection) project is a 3 years project funded by MIUR, that aims to study the aerosol attenuation of UV light in atmosphere using multiple instruments and techniques, as those commonly used in the cosmic rays community: elastic Lidar, Raman Lidar, side-scattering measurements using a distant laser source. All measurements will be acquired on the same air mass at the same time, in a semi-desertic site near Lamar, Colorado (U.S.). For each instrument, multiple analysis techniques will be tested: the target is a better comprehension of the systematics and limits of applicability of each method. The system is composed by a Lidar (e…

The boson peak

2013

The vibrational properties of glasses in the THz range differ very much from what is expected from Debye's elasticity theory: the density of states (DOS) deviates from Debye's ω2 law [the “boson peak” (BP)], the sound velocity shows a negative dispersion in the BP frequency regime and there is a strong increase in the sound attenuation near the BP frequency. These anomalies are related to an anomalous temperature dependence of the specific heat and thermal conductivity in the 10 K regime. An overview of the heterogeneous-elasticity theory is given, by means of which all these anomalies can be explained and shown to arise from the structural disorder, leading to spatial fluctuations of the s…

Continuum constitutive laws to describe acoustic attenuation in glasses

2020

International audience; Nowadays metamaterials are at the focus of an intense research as promising for thermal and acoustic engineering. However, the computational cost associated to the large system size required for correctly simulating them imposes the use of finite-elements simulations, developing continuum models, able to grasp the physics at play without entering in the atomistic details. Still, a correct description should be able to reproduce not only the extrinsic scattering sources on waves propagation, as introduced by the metamaterial microstructure, but also the intrinsic wave attenuation of the material itself. This becomes dramatically important when the metamaterial is made…

Sound attenuation and anharmonic damping in solids with correlated disorder

2010

We study via self-consistent Born approximation a model for sound waves in a disordered environment, in which the local fluctuations of the shear modulus G are spatially correlated with a certain correlation length The theory predicts an enhancement of the density of states over Debye's omega(2) law (boson peak) whose intensity increases for increasing correlation length, and whose frequency position is shifted downwards as lg. Moreover, the predicted disorder-induced sound attenuation coefficient r(k) obeys a universal scaling law F(k) = f (ke) for a given variance of G. Finally, the inclusion of the lowest-order contribution to the anharmonic sound damping into the theory allows us to rec…

Anharmonic elasticity theory for sound attenuation in disordered solids with fluctuating elastic constants

2010

Lifetime Measurements with the Doppler Shift Attenuation Method Using a Thick Homogeneous Production Target — Verification of the Method

2016

International audience; Doppler Shift Attenuation Method (DSAM) analysis of excited-state lifetimes normally employs thin production targets mounted on a thick stopper foil (“backing”) serving to slow down and stop the recoiling nuclei of interest in a well-defined manner. Use of a thick, homogeneous production target leads to a more complex analysis as it results in a substantial decrease in the energy of the incident projectile which traverses the target with an associated change in the production cross section of the residues as a function of penetration depth. Here, a DSAM lifetime analysis using a thick homogeneous target has been verified using the Doppler broadened lineshapes of γ ra…

Photoluminescence in gamma-irradiated alpha-quartz investigated by synchrotron radiation

2004

Abstract We report an experimental investigation of the photoluminescence, under excitation by synchrotron radiation within the absorption band at 7.6 eV , induced in γ-irradiated α-quartz. Two emissions centered at 4.9 and 2.7 eV are observed at low temperature: the former decreases above 40 K , whereas the second band exhibits an initial slight increase and its quenching is effective above 100 K . Furthermore, the decay kinetics of both emissions occur in a time scale of nanoseconds: at T=17.5 K we measured a lifetime τ∼1.0 ns for the photoluminescence at 4.9 eV and τ∼3.6 ns for that at 2.7 eV . These results give new insight on the optical properties associated with defects peculiar of c…