Atomic Absorption Coefficient Research Articles

Study of Effective Atomic Number, Mass Energy Absorption Coefficient and Absorbed Dose Rate in Human Organ and Tissue Substitutes

Abstract: The effective atomic number and mass energy absorption coefficient are two essential parameters used to investigate the radiation response of composite materials of dosimetric interest in many medical applications. The effective atomic number of nine selected human tissues and eleven samples of tissue substitute materials were computed using two methods, the interpolation method and the direct method in the energy range used in brachytherapy applications (0.1-2.0) MeV. The applicability of using the effective atomic number values to investigate scatter and absorption properties of some tissue substitutes, against that of the corresponding human tissues, to validate their tissue-equivalency, is examined. The effect of partial interaction cross sections is also explicitly discussed. Further, the absorbed dose rate, for an isotropic point source, in the selected tissue samples was computed using their estimated mass energy absorption coefficient values. The obtained data are analyzed and differences in sample dose rate relative to water, for photon energies of interest, are evaluated. The results indicate that numbers of tissue substitute samples yield estimates of dose rate to within 5% of dose rate of their corresponding human tissues. The obtained results are expected to be useful in improving dose calculation accuracy in brachytherapy treatment planning or dose evaluation after treatment. Keywords: Dosimetry, Human organs and tissues, Tissue equivalent materials, Equivalent atomic number, Attenuation and absorption coefficients.

Radiation shielding calculations of some selected rare earth oxides

Radiation shielding parameters of oxidized compounds of some selected rare earth elements were determined. These parameters are mass absorption coefficient, effective atomic number, electron density, half-value layer, tenth value layer, and mean free path values. A variable energy x-ray (VEX) source was used as an exciter in the system, where these basic parameters will be determined. An experimental setup was prepared in attenuation geometry. Experimentally measured and theoretically calculated mass attenuation values of the target materials were used to calculate radiation protection parameters. As can be seen from previous works, the WinXCOM program efficiently calculates theoretical atomic cross-sections and mass absorption coefficients. As a result of the search for alternatives to this software, ParShield and Phy-X programs have emerged at different times. In this study, the validity of ParShield and Phy-X programs produced as other options to the WinXCOM program were tested, and the results were found to be entirely satisfactory.

Microstructure for aqueous cesium tetraborate and rubidium tetraborate with X-ray scattering

In this study, microstructure such as intra-molecule interaction BO,OO in polyborate anions (B3O3(OH)4-, B4O5(OH)4-) and inter-molecule (BO(W),M(Rb/Cs)O, M(Rb/Cs)B and OO, M-M i.e.) interaction have been taken into consideration by model calculation with the method of X-ray scattering. The models of B3O3(OH)4-, B3O3(OH)52− and B4O5(OH)42− were optimized by DFT (density functional theory) calculation which have a good agreement with the model calculation. During the process of data analyzing, Raman spectrum, pH, density, stoichiometric volume, atomic mass absorption coefficient have also been carried out. The coordination distance and number of CsO(wI)(∼0.336 nm, ∼7.8), CsO(wII)(∼0.526 nm, ∼8.4), OO(W)(∼0.278 nm, ∼2.15) and CsB(∼0.458 nm, ∼0.9) are concerned to Cs2B4O7 solution. For aqueous Rb2B4O7 samples, the structure parameters of RbO(wI)(∼0.292 nm, ∼7.0), RbO(wII)(∼0.467 nm, ∼8.0), OO(W)(∼0.278 nm, ∼2.22), RbB(∼0.377 nm, ∼0.9) are also listed in the discussion part. And also concluded that cesium ion forms bidentate chelate complexes with tetraborate ion in the solution. Moreover, the influence of the samples, concentration on RDFs (radial distribution function curves) and the difference between cesium tetraborate and rubidium tetraborate also illustrated in paper.

Energy dependence of radiation interaction parameters of some organic compounds

Gamma rays interact with a material through photoelectric absorption, Compton scattering, Rayleigh scattering and Pair production in the intermediate energy range. The probability of occurrence of a particular type of process depends on the energy of incident gamma rays, atomic number of the material, scattering angle and geometrical conditions. Various radiological parameters for organic compounds, namely ethylene glycol (C2H6O2), propylene glycol (C3H8O2), glycerin (C3H8O3), isoamyl alcohol (C5H12O), butanone (C4H8O), acetophenone (C8H8O2), cyclohexanone (C6H10O), furfural (C5H4O2), benzaldehyde (C7H6O), cinnamaldehyde (C9H8O), glutaraldehyde (C5H8O2), aniline (C6H7N), benzyl amine (C6H7N), nitrobenzene (C6H5NO2), ethyl benzene (C8H10), ethyl formate (C3H6O2) and water (H2O) are presented at 81, 122, 356 and 511keV energies employing NaI(Tl) scintillation detector in narrow-beam transmission geometry. The radiation interaction parameters such as mass attenuation, molar extinction and mass energy absorption coefficients, half value layer, total atomic and effective electronic cross-sections and CT number have been evaluated for these organic compounds. The general trend of values of mass attenuation coefficients, half value layer, molar extinction coefficients, total atomic and effective electronic cross-sections and mass energy absorption coefficients shows a decrease with increase in incident gamma photon energy. The values of CT number are found to increases linearly with increase of effective atomic number (Zeff). The variation in CT number around Zeff ≈ 3.3 shows the peak like structure with respect to water and the correlation between CT number and linear attenuation coefficient is about 0.99. Appropriate equations are fitted to these experimentally determined parameters for the organic compounds at incident photon energy ranging from 81keV to 511keV used in the present study. Experimental values are compared with the theoretical data obtained using WinXcom software package, and are found in good agreement.

Atomic structure and optoelectronic properties of In0.53Ga0.47As (100) reconstruction surfaces: A DFT study

There are kinds of reconstructions on InGaAs(100) surface, such as As-rich β2(2×4), In-rich α(2×4), and Ga-rich α(2×4) reconstructions. In this article, the three kinds of In0.53Ga0.47As(100) reconstruction surfaces are studied based on first-principles calculations, and atomic structures, formation energies, band structures, electron distributions, and absorption coefficients were obtained. Atomic structures of the surfaces were calculated and results show that the relaxation of As-rich β2(2×4) surface is the smallest. The As-rich β2(2×4) surface also has the smallest formation energy, which means the As-rich β2(2×4) surface is the steadiest among the three surfaces. Furthermore, the energy band structures and the work function are analyzed. The less the work function is, the easier the photoelectrons escape from the surfaces. Therefore, it is the easiest for photoelectrons to escape from As-rich β2(2×4) surface due to its lowest work function. The same conclusion is also confirmed based on the calculations of the electronic structure. The negative electron affinity photocathode is mainly sensitive to the infrared region where the absorption coefficient of the As-rich β2(2×4) surface is bigger than those of the In-rich α(2×4) and Ga-rich α(2×4) surfaces. The As-rich β2(2×4) surface is benefit for the formation of the negative electron affinity In0.53Ga0.47As photocathode.

Synthesis and Characterisation of Thin Films of Bismuth Triiodide for Semiconductor Radiation Detectors

Bismuth iodide is a potentially active material for room temperature radiation detector, as it is well reported in the literature that it has both wide energy band gap and high atomic absorption coefficient. Crystalline films of high atomic number and high radiation absorption coefficient can absorb the X-rays and convert them directly into electrical charges which can be read by imaging devices. Therefore, it was proposed to grow thin films of Bismuth iodide on glass substrate using thermal evaporation technique in vacuum to avoid the inclusion of impurities in the films. The structural studies of the films were carried out using XRD and optical absorption measurement was carried out in the UV/VIS region using spectrophotometer. All Bismuth iodide films grown at room temperature are polycrystalline and show X-ray diffraction peaks at angles reported in research papers. The optical transmission spectra of BiI3 films show a high transmission of about 80% in visible region with a sharp fall near the fundamental absorption at 650 nm. Resistivity of the as-grown film was found to be around 1012 ohm-cm suitable value for X-ray detection application. Films were subjected to scanning electron microscopy to study the growth features of both as-grown and annealed films.

The effect of temperature on soot properties in premixed methane flames

The effect of flame temperature on soot properties was studied in premixed methane/oxygen flames burning at a constant mixture composition (C/O = 0.60, Φ = 2.4) and different cold-gas flow velocities (4 and 5 cm s −1). Temperature and concentration profiles of stable gases and condensed phases combustion products were measured along the flame axis. It was found that the high flame temperature conditions cause a larger decomposition of methane into hydrogen and C 2–C 4 hydrocarbons, thereby reducing the formation of benzene and condensed phases including condensed species and soot. Soot properties were studied by UV–Visible absorption spectroscopy, thermogravimetry and H/C elemental analysis. A description of soot nanostructural organization was also performed by means of high-resolution transmission electron microscopy. Different properties and nanostructures were found to develop in the soot, depending on the temperature and on soot aging associated. Soot dehydrogenation occurred to a larger extent in the high flame temperature conditions. As soot dehydrogenates the mass absorption coefficients of soot exhibited an increasing trend along the flame axis. However, mature soot retained a relatively high H/C ratio and low absorption coefficients with respect to other less hydrogenated fuels even in high temperature conditions. This indicates that the aromatization/dehydrogenation of soot in premixed flames is more dependent on the fuel characteristics rather than on the flame temperature. Generally, it was assessed that mature soot produced from diverse hydrocarbon fuels with similar flame temperatures and flame types possess a different chemical composition and structure. To this regard the H/C atomic ratio and mass absorption coefficients appeared to be signatures of soot properties and structural evolution.

Antibiofouling polymer-coated gold nanoparticles as a contrast agent for in vivo x-ray computed tomography imaging

Current computed tomography (CT) contrast agents such as iodine-based compounds have several limitations, including short imaging times due to rapid renal clearance, renal toxicity, and vascular permeation. Here, we describe a new CT contrast agent based on gold nanoparticles (GNPs) that overcomes these limitations. Because gold has a higher atomic number and X-ray absorption coefficient than iodine, we expected that GNPs can be used as CT contrast agents. We prepared uniform GNPs (∼30 nm in diameter) by general reduction of HAuCl4 by boiling with sodium citrate. The resulting GNPs were coated with polyethylene glycol (PEG) to impart antibiofouling properties, which extends their lifetime in the bloodstream. Measurement of the X-ray absorption coefficient in vitro revealed that the attenuation of PEG-coated GNPs is 5.7 times higher than that of the current iodine-based CT contrast agent, Ultravist. Furthermore, when injected intravenously into rats, the PEG-coated GNPs had a much longer blood circulation ...

Antibiofouling Polymer-Coated Gold Nanoparticles as a Contrast Agent for in Vivo X-ray Computed Tomography Imaging

Current computed tomography (CT) contrast agents such as iodine-based compounds have several limitations, including short imaging times due to rapid renal clearance, renal toxicity, and vascular permeation. Here, we describe a new CT contrast agent based on gold nanoparticles (GNPs) that overcomes these limitations. Because gold has a higher atomic number and X-ray absorption coefficient than iodine, we expected that GNPs can be used as CT contrast agents. We prepared uniform GNPs ( approximately 30 nm in diameter) by general reduction of HAuCl4 by boiling with sodium citrate. The resulting GNPs were coated with polyethylene glycol (PEG) to impart antibiofouling properties, which extends their lifetime in the bloodstream. Measurement of the X-ray absorption coefficient in vitro revealed that the attenuation of PEG-coated GNPs is 5.7 times higher than that of the current iodine-based CT contrast agent, Ultravist. Furthermore, when injected intravenously into rats, the PEG-coated GNPs had a much longer blood circulation time (>4 h) than Ultravist (<10 min). Consequently, CT images of rats using PEG-coated GNPs showed a clear delineation of cardiac ventricles and great vessels. On the other hand, relatively high levels of GNPs accumulated in the spleen and liver, which contain phagocytic cells. Intravenous injection of PEG-coated GNPs into hepatoma-bearing rats resulted in a high contrast ( approximately 2-fold) between hepatoma and normal liver tissue on CT images. These results suggest that PEG-coated GNPs can be useful as a CT contrast agent for a blood pool and hepatoma imaging.

Parameters affecting the X-ray dose absorbed by macromolecular crystals

The lifetime of a macromolecular crystal in an X-ray beam is assumed to be limited by the absorbed dose. This dose, expressed in Gray (Gy = J kg(-1)), is a function of a number of parameters: the absorption coefficients of the constituent atoms of the crystal, the number of molecules per asymmetric unit, the beam energy, flux, size and profile, the crystal size, and the total irradiation time. The effects of these variables on the predicted absorbed dose, calculated using the program RADDOSE, are discussed and are illustrated with reference to the irradiation of a selenomethionine protein crystal of unknown structure. The results of RADDOSE can and will in the future be used to inform the data collection procedure as it sets a theoretical upper limit on the total exposure time at a certain X-ray source. However, as illustrated with an example for which the experimental data are compared with prediction, the actual lifetime of a crystal could become shorter in those cases where specific damage breaks down crucial crystal contacts.

Atomic absorption with ultracold atoms

Recent advances in laser-atom cooling techniques and diode-laser technology now allow one to conduct an idealised atomic absorption experiment comprising a sample of ultracold, quasi-stationary absorbing atoms and a source of near-monochromatic resonant light. Under such conditions, the atomic absorption coefficient at line centre is independent of the oscillator strength of the atomic resonance line. This offers the prospect of ‘oscillator-strength-free’ atomic absorption spectroscopy in which the absorption signal is equally large for both strong and weak (closed) transitions of the same wavelength and in which absolute atomic absorption could be performed without knowledge of the oscillator strength. Moreover, the resolution and sensitivity for a given atom density are greatly enhanced, typically by approximately three orders of magnitude (and even more for weak transitions), compared with conventional flame or graphite-furnace atomic absorption. We describe an atomic absorption experiment based on samples of ultracold, laser-cooled caesium atoms and a narrow-bandwidth diode laser source that approximates the idealised conditions for oscillator-strength-free atomic absorption. The absorption measurements are used to determine the number density and temperature (approx. 6 μK) of the sample of ultracold atoms. Some of the technical obstacles that would have to be overcome before samples of ultracold atoms and diode laser sources could be used in analytical atomic absorption spectroscopy are discussed.

Average absorption coefficients and mean free paths of radiation of the continuous spectrum in the region of multiple and total ionization

Consideration is given to problems of averaging absorption coefficients of atoms and multiply charged ions with passage to the region of total ionization. It is shown that correct allowance for ionization of hydrogen-like ions makes it possible to pass automatically to coefficients of absorption in the continuous spectrum. A comparison is made with detailed calculations of mean free paths for a number of elements.

The Oscillator Strength in Atomic Absorption Spectroscopy

The role of the oscillator strength in atomic absorption spectroscopy, and in particular in absolute elemental analysis by atomic absorption, is discussed. A universal method for determining atomic lifetimes, and hence absolute oscillator strengths of atomic resonance lines, for almost any element in the Periodic Table is described. It is shown that for the idealized conditions of a pure natural-broadened absorption line and a monochromatic emission line, the peak atomic absorption coefficient is independent of the oscillator strength and that the oscillator strength enters into an atomic absorption signal only through extraneous broadening processes such as Doppler, collisional, and transit-time broadening. An atomic absorption experiment, based on samples of near-stationary laser-cooled atoms and a near-monochromatic diode-laser light source, that satisfies the requirements for “oscillator-strength-free” atomic absorption is described.

On-line atomization of selenium hydride in graphite furnaces: estimate of atomic absorption coefficient and spectroscopic temperature

A transversely heated graphite tube atomizer (THGA) has been employed to ensure constant temperature within the observation volume. A method of sampling of gaseous selenium hydride from a container has been developed including a relation between observed peak area (integrated absorbance) and selenium mass injected into the furnace. This makes it possible to control fully the composition of the atomizer atmosphere. A boron nitride tube sealed to the injection hole of the graphite tube has been used as the interface. It performed well even at the highest tested atomization temperature (2400°C). Spectroscopic temperature measurements based on atomic absorption at the 196.1 nm and 204.0 nm Se lines have been used to determine the influence of carrier gas flow rates on the effective gas phase temperature in the atomizer at set furnace temperatures of 1800°C and 2200°C. Characteristic masses m 0 at the 196.1 nm line, in pure argon atmosphere, have been determined at these set furnace temperatures for various argon gas flow rates. The data are employed to estimate an experimental value of the atomic absorption coefficient: (17.1 ± 0.8) × 10 −18 m 2. The value does not significantly differ from the theoretical value. m 0 values found for the temperature range 1800–2400°C for the hydride injection into the furnace at the minimum feasible carrier gas flow rate are compared with characteristic masses for the traditional liquid sampling to the furnace in the same temperature range. This made it possible to estimate that the analyte losses through the injection port in the case of the traditional liquid sampling to the furnace are in the range 20–25%.

On the applicability of optical depth-atomic absorption relationship to measurements of alkali seeded combustion flames

The applicability of the new depth-atomic absorption relationship to measurements of optical properties of an alkali metal in a non-uniform multi-component combustion flame was numerically studied. The relationship describes the equality between the ratio of the optical depths at far to near wing wavelengths and that of the atomic absorption coefficients at the respective wavelengths. An introduction of biases into theoretical wing intensities and the evaluation of the ratio of the atomic absorption coefficients with far wing temperatures are essential features in the formalism. It is shown that the relationship has sufficient sensitivities to the change of optical quantities to be measured under realistic flame pressures, temperatures and wing spectral levels when the two wavelengths are adequately separated.

New Relationships for Emission-Absorption Measurements of Alkali-Seeded Combustion Gases.

Numerical studies on emission-absorption measurements of potassium-seeded kerosene-oxygen combustion gases were carried out. It was found that the ratio of the optical thicknesses at two arbitrary wing wavelengths of the potassium 766.5 nm resonance line was nearly equal to the ratio of the respective atomic absorption coefficients which were calculated based on the temperature measured by the emission-absorption method at the far-wing wavelength. Using the formula, the optical collision cross section as well as the pressure and Doppler broadenings of the potassium doublet could be predicted theoretically with an error of less than one percent. The optimal difference between the far-and near-wing wavelengths is 1.0-2.0 nm. The error in the above optical quantities and also the seed atom number density are insensitive to the near-wing wave-length.

Analyses without calibration curve for determination of indium in sediment and geochemical samples

Influences of atomization temperatures on the characteristic mass and the atomic absorption coefficient of indium were studied. The results show that the values of characteristic mass obtained from the wall, using the platform and the V-shaped boat have appeared to be stable to better than 10, 6 and 12% in the range of 1600–2400 °C, respectively. The determination of indium without calibration curve by furnace with the V-shaped boat using palladium and ammonium salt of EDTA as a matrix modifier are described. The proposed method was applied to the determination of indium in standard sediment and geochemical reference samples and satisfactory results were obtained.

Application of standardless analysis in graphite furnace atomic absorption spectrometry: Determination of chromium

Influences of atomization temperatures on the characteristic mass and the atomic absorption coefficient of chromium were studied. The experimental results show that the values of characteristic mass have appeared to be stable to better than 10% when the analyte is atomized in the range of 2500–2800°. The standardless analysis was applied to the determination of chromium in standard sediment and geochemical reference samples and satisfactory results were obtained.

Mono-standard calibration approach to multi-element XRF analysis of thin films using polychromatic excitation

A reliable method is described for the calculation of slopes of calibration lines for thin-film samples using polychromatic excitation. Theoretically calculated slopes for elements within one series, e.g. the K-series, are normalized using one or two known slopes for elements in the series. The mathematical equations used to interpolate slopes as a function of atomic number are based on the fundamental relationship between fluorescent intensity and atomic number, fluorescent yield, detector efficiency, concentration and mass absorption coefficients. Kramer's formula is used to approximate the shape of the primary radiation spectrum. The method was applied to the analysis of thin films.

Characterization Of Boron Films Prepared By Chemical Vapor Deposition And Their Application In X-Ray Imaging

AbstractBoron, a low Z element, is useful for x-ray optics since it has a low atomic absorption coefficient. Boron films prepared by chemical vapor deposition were characterized optically, electronically and mechanically. Auger, infrared and hydrogen effusion analyses showed that the films are amorphous hydrogenated boron. The hydrogen content ranges from 8–71%. The measurements of the complex refractive index and the resistance vs. temperature determined that they are a typical amorphous semiconductor with the energy gap ranging from 1.09 to 1.36 eV, decreasing with increasing hydrogen content and with the Fermi energy level pinned about midgap. The real refractive index at 490 nm increases from 3.25–3.59 with increasing hydrogen content. The Young's modulus and hardness were found to be 3.05 × 1013 dyne/cm2 and around 2500 Vickers, respectively. The chemical tests suggested that boron films are stable in nonoxidizing bases and concentrated acids. Some oxidizing bases such as basic ferricyanide and permanganate solutions are good etchants for CVD boron films. Boron coated beryllium x-ray windows which have enhanced resistance to degradation are now commercially available, and self-supporting boron windows are potential future products for x-ray imaging.