Search results for "Absorption cross section"

<title>Iodine and bromine resonance lamps in atmospheric research</title>

2003

For the first time previously developed iodine resonance spectra source has been tested in flash photolysis experiment. Quantitative measurements of concentration kinetics of iodine atomic species in a I2+O3 system are possible. The 183.038 nm resonance absorption transition of I(2P3/2) in previously developed EDL has been studied; dependence of self-absorption and self-reversal on iodine partial pressure in the discharge volume has been measured. The search for optimal conditions for an iodine EDL with minimized self-absorption and sufficient intensity were made. In condition of flash photolysis with previously described method it is possible to determine the emission temperature, oscillat…

FluorMODleaf: A new leaf fluorescence emission model based on the PROSPECT model

2010

International audience; A new model of chlorophyll a fluorescence emission by plant leaves, FluorMODleaf, is presented. It is an extension of PROSPECT, a widely used leaf optical properties model that regards the leaf as a pile of N absorbing and diffusing elementary plates. In FluorMODleaf, fluorescence emission of an infinitesimal layer of thickness dx is integrated over the entire elementary plate. The fluorescence source function is based on the excitation spectrum of diluted isolated thylakoids and on the emission spectra of isolated photosystems, PSI and PSII, which are the main pigment–protein complexes involved in the initial stages of photosynthesis. Scattering within the leaf is p…

DOAS Measurements of Iodine Oxides in the Framework of the MAP (Marine Aerosol Production) Project

2007

Estimation of the emission temperature of an electrodeless discharge lamp and determination of the oscillator strength for the I(2P3/2) 183.038 nm re…

2001

Abstract The 183.038 nm resonance absorption transition of I( 2 P 3/2 ) has been studied using a flash photolysis set-up for gas-phase chemistry and a radio frequency powered electrodeless discharge lamp filled with iodine. The dependence of self-absorption and self-reversal on iodine partial pressure in the discharge volume was measured. The optimum iodine partial pressure, with self-absorption minimized and acceptable intensity, is determined to be approximately 2.5×10 −3 mbar. A method is described to estimate the temperature of the emitting atoms using direct measurements of relative absorption at different absorber concentrations. This yields an emission temperature of 923±50 K. Using …

Vacuum-ultraviolet absorption of amorphousSiO2: Intrinsic contribution and role of silanol groups

2008

We present a study on the vacuum-ultraviolet (VUV) absorption properties of amorphous ${\text{SiO}}_{2}$ $(a{\text{-SiO}}_{2})$ with high concentrations of silanol groups (Si-OH). We found that the absorption spectra are made up of a couple of exponential profiles. The first, in the range from $\ensuremath{\sim}7.5$ to $\ensuremath{\sim}8.1\text{ }\text{eV}$, was attributed to Si-OH group absorption, while the second, in the range from $\ensuremath{\sim}8.1$ to $\ensuremath{\sim}8.25\text{ }\text{eV}$, was ascribed to the intrinsic absorption. The VUV absorption cross section of Si-OH groups in $a{\text{-SiO}}_{2}$ was determined as well. The intrinsic absorption was found to be affected by…

Far infrared absorption by acoustic phonons in titanium dioxide nanopowders

2006

We report spectral features of far infrared electromagnetic radiation absorption in anatase TiO2 nanopowders which we attribute to absorption by acoustic phonon modes of nanoparticles. The frequency of peak excess absorption above the background level corresponds to the predicted frequency of the dipolar acoustic phonon from continuum elastic theory. The intensity of the absorption cannot be accounted for in a continuum elastic dielectric description of the nanoparticle material. Quantum mechanical scale dependent effects must be considered. The absorption cross section is estimated from a simple mechanical phenomenological model. The results are in plausible agreement with the absorption b…

Effects of spatial dispersion and damping on exciton absorption

1986

Exciton absorption is studied in the spatially dispersive case. The energy-propagation properties of the medium are used to define the absorption coefficient. The interplay of dispersion and damping in determining the absorption coefficient is discussed and a critical value of the damping above which the dispersion effects disappear is derived analytically. Furthermore, the dependence of the spectral and of the integrated absorption coefficient on the auxiliary boundary condition is discussed.

Pion vs. photon absorption on the deuteron

1995

Abstract Using an NN → ΔN transition potential fixed by the reaction pp ↔ dπ+ a good agreement can be obtained also for the reaction γd → pn in the Δ region. Further it is seen that the πNΔ and ϱNΔ parameters of the widely used Bonn potential, fitting the NN sector, yield a transition potential too weak to reproduce the pion production or absorption cross section.

Photofission of235U and238U at intermediate energies: absolute cross sections and fragment mass distributions

1994

The total photofission cross section σγ,F for235U and238U has been measured in the energy range 50≤E γ≤800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 4π arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section σγF , which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections σγ,F normalized to the atomic numberA for both isotopes coincide, and agree in theΔ-resonance region, within the systematic errors,…

Determination of the total photo-absorption cross section of 197Au from () reaction cross sections

1984

Abstract Cross sections for the reactions 197Au ( γ, ℩ n ) (x ⩽ 12) have been measured for bremsstrahlung end-point energies in the range 60–340 MeV. From these dominant cross sections, the total photon absorption cross section is determined using a cascade-evaporation calculation to account for the missing reaction channels. The enhancement factor for the classical E1 sum rule is found to be 0.93 ± 0.10.