Absorption Correction Research Articles

The Spectrophotometry Determination of Rutin and Quercetin in Mixtures

Summary The ultra-violet absorptions of rutin and quercetin have been investigated. A rapid method has been developed for the accurate determination of the minor constituent of binary mixtures of rutin and quercetin, and a formula derived for the correction of the gross absorption for the absorption due to the minor constituent. A comparison has been made between American methods of assay and the method in use in this laboratory.

Experimental determination of the self-absorption factor for MTR plates by passive gamma spectrometric measurement

The measurement of the absolute activity or the mass of radioactive substances by gamma spectrometry needs to include a correction for the radiation absorption inside the source volume, the so-called self-absorption factor. It depends on geometry and material composition of the source, the detector geometry and on the geometrical arrangement of source and gamma radiation detector; it can be calculated if full information about all that is available. This article however describes how to determine the self-absorption factor from measurements if the radiation sources are plates of uranium fuel with typical parameters of nuclear fuel for MTR reactors and without using detail information on the source geometry, thus allowing easy inspection without relying on – potentially falsified – declarations on the internal properties of the fuel objects and without calculation.

SDSS surface photometry of M 31 with absorption corrections

The objective of this work is to obtain an extinction-corrected distribution of optical surface brightness and colour indices of the large nearby galaxy M 31 using homogeneous observational data and a model for intrinsic extinction. We process the Sloan Digital Sky Survey (SDSS) images in ugriz passbands and construct corresponding mosaic images, taking special care of subtracting the varying sky background. We apply the galactic model developed in Tempel et al. (2010) and far-infrared imaging to correct the photometry for intrinsic dust effects. We obtain observed and dust-corrected distributions of the surface brightness of M 31 and a map of line-of-sight extinctions inside the galaxy. Our extinction model suggests that either M 31 is intrinsically non-symmetric along the minor axis or the dust properties differ from those of the Milky Way. Assuming the latter case, we present the surface brightness distributions and integral photometry for the Sloan filters as well as the standard UBVRI system. We find the following intrinsic integral colour indices for M 31: (U-B)_0=0.35; (B-V)_0=0.86; (V-R)_0=0.63; (R-I)_0=0.53; the total intrinsic absorption-corrected luminosities of M 31 in the B and the V filters are 4.10 and 3.24 mag, respectively.

Charm and bottom production in inclusive double Pomeron exchange in heavy-ion collisions at energies available at the CERN Large Hadron Collider

The inclusive double Pomeron exchange cross section for heavy quark pair production is calculated for nucleus-nucleus collisions at the LHC. The present estimate is based on hard diffractive factorization, corrected by absorptive corrections and nuclear effects. The theoretical uncertainties for nuclear collisions are investigated and a comparison to other approaches is presented. The production channels producing a similar final state configuration are discussed as well.

The VIMOS VLT Deep Survey: star formation rate density of Lyαemitters from a sample of 217 galaxies with spectroscopic redshifts 2 ≤ z ≤ 6.6

Aims. The aim of this work is to study the contribution of the Ly-a emitters (LAE) to the star formation rate density (SFRD) of the Universe in the interval 2<z<6.6. Methods. We assembled a sample of 217 LAE from the Vimos-VLT Deep Survey (VVDS) with secure spectroscopic redshifts in the redshift range 2 < z < 6.62 and fluxes down to F=1.5x10^18 erg/s/cm^2. 133 LAE are serendipitous identifications in the 22 arcmin^2 total slit area surveyed with the VVDS-Deep and the 3.3 arcmin^2 from the VVDS Ultra-Deep survey, and 84 are targeted identifications in the 0.62 deg^2 surveyed with the VVDS-DEEP and 0.16 deg^2 from the Ultra-Deep survey. Among the serendipitous targets we estimate that 90% of the emission lines are most probably Ly-a, while the remaining 10% could be either [OII]3727 or Ly-a. We computed the LF and derived the SFRD from LAE at these redshifts. Results. The VVDS-LAE sample reaches faint line fluxes F(Lya) = 1.5x1^18 erg/s/cm^2 (corresponding to L(Lya)=10^41 erg/s at z~3) enabling the faint end slope of the luminosity function to be constrained to a=-1.6+-0.12 at redshift z~2.5 and to a=-1.78+0.1-0.12 at z=4, placing on firm statistical grounds trends found in previous LAE studies, and indicating that sub-L* LAE contribute significantly to the SFRD. The projected number density and volume density of faint LAE in 2<z<6.6 with F>1.5x10^18 erg/s/cm^2 are 33 galaxies/arcmin^2 and 4x10^-2 Mpc^-3, respectively. We find that the the observed luminosity function of LAE does not evolve from z=2 to z=6. This implies that, after correction for the redshift-dependent IGM absorption, the intrinsic LF must have evolved significantly over 3 Gyr. The SFRD from LAE contributes to about 20% of the SFRD at z =2-3, while the LAE appear to be the dominant source of star formation producing ionizing photons in the early universe z>5-6, becoming equivalent to that of Lyman Break galaxies.

Whole Blood Thallium Determination by GFAAS with High-Frequency Modulation Polarization Zeeman Effect Background Correction

A new technique of blood thallium direct determination based on graphite furnace atomic absorption spectrometry with Zeeman background absorption correction system was designed. The developed technique does not require sample digestion. Sample treatment includes only a fivefold per volume dilution of blood sample with 0.1% (m/v) Triton X-100. L'vov integrated platform was modified with 400 μg of Rh. Matrix modifier (200 μg NH(4)NO(3) and 160 μg Pd(NO(3))(2)) was suggested for coping chloride and blood organic matter interferences. Standard reference material (Clincheck® Plasma Control for trace elements) analysis was used for validation. Additional validation was performed by analyzing spiked blood samples in the whole dynamic range. The dynamic range was 2-50 μg/L. Precision (RSD) was found <12%. Blood thallium limit of detection was 0.2 μg/L.

A revised scale model reverberation chamber for measurements of scattering coefficients.

For measurements of random‐incidence scattering coefficients according to ISO 17497‐1, scale models have proven to yield results with reasonable time and effort. Especially, handling the samples becomes much easier so that several measurements, which may be difficult or even unfeasible in a full‐scale reverberation chamber, turn out to be possible. Despite these advantages, using a scale model environment poses other difficulties that are related to the extended frequency range. In order to achieve a better repeatability and stability of the measurements, a revised scale model room is proposed. As a further development from the ordinary scale model rooms, the turntable can now be lowered so that the rotating base plate is mounted flush with the floor. The previously used hanging panels have been replaced with wall‐panel diffusers. Furthermore, the chamber includes temperature and humidity sensors to enable correction for air absorption. Measurements in the new model room are performed to evaluate the quality of the results compared with reference data from calculation and the repeatability of the measurements. Results will be compared for different room setups.

Comparison of erythemal UV irradiances from Ozone Monitoring Instrument (OMI) and ground‐based data at four Thai stations

The Ozone Monitoring Instrument (OMI), on board the NASA EOS Aura spacecraft since July 2004, provides a global view of surface spectral ultraviolet (UV) irradiance at 305, 310, 324, and 380 nm; erythemal dose rate both at overpass time and local noontime; and erythemal daily dose. Previous studies have shown comparisons of the OMI erythemal UV irradiances and ground‐based UV measurements in areas of midlatitude and high latitudes, predominantly in the Northern Hemisphere. In this study the noontime erythemal UV dose rates retrieved from OMI and measured from broadband instruments at four sites in Thailand were compared. The comparisons show a positive bias for the OMI data with respect to the ground‐based measurements. The differences between the two data sets were 30%–60% for all data and were 10%–40% for cloudless data. The differences for the cleanest site showed better agreement than those for the more urban sites. Using the Libradtran radiative transfer model, we show that aerosol is responsible for much of the positive bias in polluted areas. Since absorbing aerosol is not taken into account in the OMI surface UV algorithm, aerosol absorption correction factors have been introduced as a function of aerosol absorption optical thickness provided by OMI to improve the OMI UV data for urban and maritime sites. The differences between the corrected erythemal UV data and the ground‐based data were reduced to less than 20%.

3D elemental distribution images by XRFμCT at LNLS—Brazil

An X-ray Transmission Microtomography (CT) system combined with an X-ray Fluorescence Microtomography (XRFμCT) system was implemented in the Brazilian Synchrotron Light Laboratory (LNLS), Campinas, Brazil. The main objective of this work is to determine the elemental distribution in biological samples (breast, prostate and lung samples) in order to verify the concentration of some elements correlated with characteristics and pathology of each tissue observed by the transmission CT. The experiments were performed at the X-Ray Fluorescence beamline (D09B-XRF) of the Brazilian Synchrotron Light Laboratory, Campinas, Brazil. A quasi-monochromatic beam produced by a multilayer monochromator was used as an incident beam. The sample was placed on a high precision goniometer and translation stages that allow its rotation as well as translation perpendicular to the beam. The fluorescence photons were collected with an energy dispersive HPGe detector placed at 90° to the incident beam, while transmitted photons were detected with a fast Na(Tl) scintillation counter placed behind the sample on the beam direction. The CT images were reconstructed using a filtered back-projection algorithm and the XRFμCT were reconstructed using a filtered back-projection algorithm with absorption corrections. The 3D images were reconstructed using the 3D-DOCTOR software.

Monte Carlo simulation of the effect of miniphantom on in‐air output ratio

The aim of the study was to quantify the effect of miniphantoms on in-air output ratio measurements, i.e., to determine correction factors for in-air output ratio. Monte Carlo (MC) simulations were performed to simulate in-air output ratio measurements by using miniphantoms made of various materials (PMMA, graphite, copper, brass, and lead) and with different longitudinal thicknesses or depths (2-30 g/cm2) in photon beams of 6 and 15 MV, respectively, and with collimator settings ranging from 3 x 3 to 40 x 40 cm2. EGSnrc and BEAMnrc (2007) software packages were used. Photon energy spectra corresponding to the collimator settings were obtained from BEAMnrc code simulations on a linear accelerator and were used to quantify the components of in-air output ratio correction factors, i.e., attenuation, mass energy absorption, and phantom scatter correction factors. In-air output ratio correction factors as functions of miniphantom material, miniphantom longitudinal thickness, and collimator setting were calculated and compared to a previous experimental study. The in-air output ratio correction factors increase with collimator opening and miniphantom longitudinal thickness for all the materials and for both energies. At small longitudinal thicknesses, the in-air output ratio correction factors for PMMA and graphite are close to 1. The maximum magnitudes of the in-air output ratio correction factors occur at the largest collimator setting (40 x 40 cm2) and the largest miniphantom longitudinal thickness (30 g/cm2): 1.008 +/- 0.001 for 6 MV and 1.012 +/- 0.001 for 15 MV, respectively. The MC simulations of the in-air output ratio correction factor confirm the previous experimental study. The study has verified that a correction factor for in-air output ratio can be obtained as a product of attenuation correction factor, mass energy absorption correction factor, and phantom scatter correction factor. The correction factors obtained in the present study can be used in studies involving in-air output ratio measurements using miniphantoms.

Quantitation in Bioluminescence Imaging by Correction of Tissue Absorption for Experimental Oncology

We have developed a method of quantitation for correcting tissue absorption in in vivo bioluminescence imaging (BLI). Variations of luciferin emission spectrum were determined and were related to photon absorption to determine a correction curve. This was validated by combining BLI with tomoscintigraphy and tomodensitometry, which were applied to a lymphoma model. Tissue absorption affects luciferin emission spectrum, mainly for wavelengths less than 620 nm. So, we have selected two filters bordering 620 nm to quantify spectral modifications. A significant correlation was obtained between the spectral analysis and the percentage of transmitted light through tissues (R(2) = 0.97). On a disseminated tumour model, we have shown that such a methodology is of great interest to compare bioluminescent signals and to get more accurate quantitative data about tumour proliferation. Spectral analysis allows improved quantitation of BLI and could be of value to perform pharmacological studies and to follow tumour progression in models with tumours evolving in different locations.

Efficiency in the calculation of absorption corrections for cylinders

Efficiency in the numerical calculation of absorption corrections for cylinders has been examined. Two mathematical expressions for the correction factors have been evaluated by two methods for numerical integration. It has been found that the Gauss–Legendre quadrature applied to the formula proposed by Thorkildsen &amp; Larsen [Acta Cryst.(1998), A54, 172–185] gives results with relative errors ≤10−6, using 12 × 12 terms in the numerical integration. The conventional approach, using Simpson's method in conjunction with the formula given by Dwiggins [Acta Cryst.(1975), A31, 146–148] for the absorption correction, is far less efficient.

An improved approach to quantitative X-ray microanalysis in (S)TEM: Thickness dependent k-factors

Quantifying energy-dispersive X-ray (EDX) spectra acquired in a transmission electron microscope can produce inconsistent and unreliable results even if correct values for specimen thickness and density are being used for calculating an appropriate absorption and fluorescence correction. This can be due to various factors, such as incorrect k-factors, faulty absorption corrections due to specimen roughness, specimen buckling or wrong estimates of the detector's take-off angle, complicated fluorescence effects not accounted for in the software etc. For a thorough investigation of the InGaAs system, wedge shaped specimens were cleaved from GaAs and InAs wafers and studied by EDX spectroscopy in a JEOL2010F instrument, with thicknesses ranging from a few nanometres up to several microns. The thickness dependence of the relative intensities of X-ray lines that remains after nominal absorption and fluorescence correction were taken into account could be used to perform linear least-squares fits, thereby eliminating to a first order the apparent remaining thickness dependence of the k-factors. The resulting fits demonstrate this correction improves the quantification of the chemical concentrations of indium and gallium in InGaAs samples of known thickness to 1at%.

Absorption correction for cylindrical and annular specimens and their containers or supports

The absorption correction for cylindrical specimens, typically capillary or annular, is affected by absorption in both the specimen and the supporting material. These corrections are calculated here using numerical integration of the lengths through the different regions of the specimen that the beam traverses. Suitable formulae have been derived and built in to a computer program for calculating the absorption correction for a range of cylindrical geometries. The influence of absorption in the support is most significant for annular specimens on a highly absorbing core, and for capillary specimens of highly absorbing compounds. The error arising from neglecting absorption in the specimen and additionally in the capillary is demonstrated in Rietveld refinements of LaB6. Interpolation of correction factors between values calculated at discrete θ intervals, and θ offsets arising from absorption, are also discussed.

Total and diffractive cross sections in enhanced Pomeron scheme

For the first time, a systematic analysis of the high energy behavior of total and diffractive proton-proton cross sections is performed within the Reggeon field theory framework, based on the resummation of all significant contributions of enhanced Pomeron diagrams to all orders with respect to the triple-Pomeron coupling. The importance of different classes of enhanced graphs is investigated, and it is demonstrated that absorptive corrections due to ``net''-like enhanced diagrams and due to Pomeron ``loops'' are both significant and none of those classes can be neglected at high energies. A comparison with other approaches based on partial resummations of enhanced diagrams is performed. In particular, important differences are found concerning the predicted high energy behavior of total and single high mass diffraction proton-proton cross sections, with our values of ${\ensuremath{\sigma}}_{pp}^{\mathrm{tot}}$ at $\sqrt{s}=14\text{ }\text{ }\mathrm{TeV}$ being some 25%--40% higher and with the energy rise of ${\ensuremath{\sigma}}_{\mathrm{HM}}^{\mathrm{SD}}$ saturating well below the LHC energy. The main causes for those differences are analyzed and explained.

XRD total pattern fitting applied to study of microstructure of TiO2films

New XRD total pattern fitting softwareMSTRUCTwas used to study the microstructure of magnetron-deposited TiO2thin films.MSTRUCTis an extension of theFOXprogram for structure determination from powder diffraction data.MSTRUCTmakes corrections for refraction and absorption, residual stress, and preferred orientation that are necessary for thin-film analysis using the parallel-beam geometry and an asymmetric detector scan with small angles of incidence. The program also corrects for crystallite size broadening in terms of log-normal distribution, two models of strain (phenomenological and dislocation models), as well as the influence of stacking faults in the most common cubic and hexagonal structures. The microstructure results obtained by this study show that during crystallization of the amorphous TiO2films, tensile stresses were generated resulting in anisotropic shifts of diffraction peaks. This was confirmed byin situcrystallization and direct stress measurements. The consideration of the stress effect in terms of the weighted Reuss-Voigt model improved the fits significantly. The stresses were found to depend systematically on the TiO2film thickness, and their values determined by total pattern fitting agree well with the values measured directly by XRD stress analysis.

Estimate of the single diffractive heavy quark production in heavy ion collisions at the CERN LHC

The single diffractive cross section for heavy quarks production is calculated at next-to-leading order (for nucleus-nucleus collisions. Such processes are expected to occur at the LHC, where the nuclei involved are lead at $\sqrt{s}=5.5\text{ }\text{ }\mathrm{TeV}$ and calcium at $\sqrt{s}=6.3\text{ }\text{ }\mathrm{TeV}$. We start using the hard diffractive factorization formalism, taking into account a recent experimental parametrization for the Pomeron structure function (DPDF). Absorptive corrections are accounted for by the multiple Pomeron contributions considering a gap survival probability, where its theoretical uncertainty for nuclear collisions is discussed. We estimate the diffractive ratios for the single diffraction process in nuclear coherent/incoherent collisions at the LHC.

Radiological responses of different types of Egyptian Mediterranean coastal sediments

The aim of this study was to identify gamma self-absorption correction factors for different types of Egyptian Mediterranean coastal sediments. Self-absorption corrections based on direct transmission through different thicknesses of the most dominant sediment species have been tested against point sources with gamma-ray energies of 241Am, 137Cs and 60Co with 2% uncertainties. Black sand samples from the Rashid branch of the Nile River quantitatively absorbed the low energy of 241Am through a thickness of 5 cm. In decreasing order of gamma energy self-absorption of 241Am, the samples under investigation ranked black sand, Matrouh sand, Sidi Gaber sand, shells, Salloum sand, and clay. Empirical self-absorption correction formulas were also deduced. Chemical analyses such as pH, CaCO 3, total dissolved solids, Ca 2+, Mg 2+, CO 3 2−, HCO 3 − and total Fe 2+ have been carried out for the sediments. The relationships between self absorption corrections and the other chemical parameters of the sediments were also examined.

Chemical analysis of nickel silicides with high spatial resolution by combined EDS, EELS and ELNES

The purpose of this study is to develop methodologies for the characterization of Ni-silicides by analytical TEM techniques. The measurements are performed in STEM mode to allow a good spatial resolution. Initial examination of the Ni-silicide phases is done by energy-dispersive X-ray spectroscopy (EDS). It is shown that quantification results with high accuracy and precision are obtained when a Ni-silicide reference layer is used as a standard, and an absorption correction is applied to the data. The EDS quantification results are then used as a reference for the quantitative electron energy-loss spectroscopy (EELS) analysis. It is shown that EELS analysis yields quantification results with high accuracy and precision, when the EELS data are treated with a model based approach. The EELS analysis is combined with a study of the Ni-L2,3 near-edge structure (ELNES). The ELNES of the phases can be distinguished either visually or by calculating the branching ratio from the spectra with the model based approach. This paper shows that the different Ni-silicide phases can be distinguished with these EELS based methods. The accuracy and precision of the EDS and EELS results are compared.

Comparison of experimental and theoretical X-ray intensities from (In)GaAs specimens investigated by energy-dispersive X-ray spectroscopy in a transmission electron microscope

Experimental measurements of X-ray line intensity ratios in a transmission electron microscope are compared over several orders of magnitude of sample thicknesses, from the nm- to the mm- range, with Monte-Carlo simulations using two different software packages. It is shown that the form of the thickness dependence of the K/L ratio of characteristic X-ray lines for GaAs is reproduced qualitatively, but the numerical differences between software packages are large. A scheme is presented for improving the simple k-factor method, taking explicitly into account the thickness dependence that remains even after application of the usual absorption and fluorescence corrections. This is done in first-order approximation by linear regression. The improvement in determining the correct indium concentration in specimens of InGaAs is calculated to be 1at%.