Gamma ray shielding capabilities of rhenium-based superalloys

ABSTRACT

Because of the high radiation dose in applications involving nuclear reactors, medical treatments etc., it is important to reduce the exposure to radiation of areas and workers. In this study, we were examined gamma ray shielding parameters of the newly produced Re-based superalloys. Mass attenuation coefficient (µ/ρ) of the alloys were obtained experimentally at 81, 276, 302, 356, 383 keV photon energies emitted from ¹³³Ba radioactive source using Ultra Ge detector. The experimental results were compared with the values obtained by the WinXCOM program and were found to be in perfect agreement with each other. Additionally, effective atomic number (Z_eff) and electron density (N_eff) were determined for produced Rhenium (Re) based super alloys in the energy range 1 keV–100?GeV. S5 sample which has maximum Rhenium percentage own the largest µ/ρ and Z_eff values. Moreover, by using Geometric Progression (GP) approximation, EABF and EBF were computed for the superalloys depending on the energy and penetration depths. It has been deduced that the values of EABF and EBF are minimum in the medium energy region. EBF and EABF values of the alloys have changed depending on the equivalent atomic number. Among alloy samples under study, S5 superalloy is the best for gamma ray shielding. However, in general, considering the radiation energies used in many applications, all the alloys under study have satisfactory radiation absorption properties.     

Gamma or X-rays attenuation properties of some biochemical compounds

The probability of gamma or X-ray interactions with important 14 antioxidants have been discussed for total photon interactions in the wide energy range of 1?keV–100?GeV using the WinXCOM code. The variations of mass attenuation coefficient (μ_ρ), effective atomic number (Z_eff) and electron density (N_el) with photon energy were plotted for total photon interactions. It was found that the values of μ_ρ, Z_eff and N_el depend on the incoming photon energy and chemical compositions of antioxidant. The highest values of these parameters were found at a low-energy zone where the photoelectric effect is the dominant interaction process. When antioxidants were compared with each other, it was seen that Z_eff has the highest values for Oenin chloride and Delphinidin chloride which contain the Cl element. This investigation is thought to be useful for medical applications where radiation exposure is present.     

Measurement of photon interaction parameters of high-performance polymers and their composites

In the present study, commercially important high-performance polymers and their composites have been investigated with respect to photon interactions as means of mass attenuation coefficient (μ/ρ), mean free path (MFP), half-value layer (HVL), effective atomic number (Z_eff), effective electron density (N_eff), and energy absorption and exposure buildup factors (EABF and EBF) at different photon energies. For this purpose, sample plates were prepared by extrusion and injection techniques using polyethersulfone, polyetherimide, acrylonitrile butadiene styrene copolymer, polyamide 66, polyphthalamide, and polypropylene copolymers as high-performance polymers and glass and carbon fibers as reinforcement. The (μ/ρ)s of the materials were measured at 81 and 356?keV photon energies to determine MFP, HVL, Z_eff, and N_eff. The theoretical values of these parameters were calculated via ZXCOM, WinXCom and Monte Carlo N-Particle simulation code (MCNP), and a good agreement was obtained between WinXCom–MCNP and MCNP–Exp. Finally, EABFs and EBFs of the samples were calculated up to around 40 MFP in the energy region 0.015–15?MeV and significant variations were observed in the continuous energy and MFP regions.     

In situ electrochemical high‐energy X‐ray diffraction using a capillary working electrode cell geometry

The ability to generate new electrochemically active materials for energy generation and storage with improved properties will likely be derived from an understanding of atomic‐scale structure/function relationships during electrochemical events. Here, the design and implementation of a new capillary electrochemical cell designed specifically for in situ high‐energy X‐ray diffraction measurements is described. By increasing the amount of electrochemically active material in the X‐ray path while implementing low‐Z cell materials with anisotropic scattering profiles, an order of magnitude enhancement in diffracted X‐ray signal over traditional cell geometries for multiple electrochemically active materials is demonstrated. This signal improvement is crucial for high‐energy X‐ray diffraction measurements and subsequent Fourier transformation into atomic pair distribution functions for atomic‐scale structural analysis. As an example, clear structural changes in LiCoO₂ under reductive and oxidative conditions using the capillary cell are demonstrated, which agree with prior studies. Accurate modeling of the LiCoO₂ diffraction data using reverse Monte Carlo simulations further verifies accurate background subtraction and strong signal from the electrochemically active material, enabled by the capillary working electrode geometry.     

Determination of effective atomic number and electron density of heavy metal oxide glasses

The effective atomic number (Z_eff) and effective electron density (N_eff) of eight heavy metal oxide (HMO) glasses have been determined using the Monte Carlo simulation code MCNP for the energy range of 10?keV–10?MeV. The interpolation method was employed to extract Z_eff and N_eff values from the simulation and that calculated with the help of XCOM program. Comparisons are also made with predictions from the Auto-Z_eff software in the same energy region. Wherever possible, the simulated values of Z_eff and N_eff are compared with experimental data. In general, a very good agreement was noticed. It was found that the Z_eff and N_eff vary with photon energy and do not have extended intermediate regions where Compton scattering is truly dominating; only dips slightly above ～1.5?MeV were recorded. Z_eff and N_eff are found to increase with PbO and Bi₂O₃ contents. It was found that the Z_eff value rather than the N_eff value is a better indicator for PbO and/or Bi₂O₃ contents.     

Effect of gamma irradiation on X‐ray absorption and photoelectron spectroscopy of Nd‐doped phosphate glass

X‐ray absorption near‐edge structure (XANES) and X‐ray photoelectron spectroscopy (XPS) of Nd‐doped phosphate glasses have been studied before and after gamma irradiation. The intensity and the location of the white line peak of the L₃‐edge XANES of Nd are found to be dependent on the ratio O/Nd in the glass matrix. Gamma irradiation changes the elemental concentration of atoms in the glass matrix, which affects the peak intensity of the white line due to changes in the covalence of the chemical bonds with Nd atoms in the glass (structural changes). Sharpening of the Nd 3d_5/2 peak profile in XPS spectra indicates a deficiency of oxygen in the glasses after gamma irradiation, which is supported by energy‐dispersive X‐ray spectroscopy measurements. The ratio of non‐bridging oxygen to total oxygen in the glass after gamma radiation has been found to be correlated to the concentration of defects in the glass samples, which are responsible for its radiation resistance as well as for its coloration.     

X‐ray fluorescence induced by standing waves in the grazing‐incidence and grazing‐exit modes: study of the Mg–Co–Zr system

The characterization of Mg–Co–Zr tri‐layer stacks using X‐ray fluorescence induced by X‐ray standing waves, in both the grazing‐incidence (GI) and the grazing‐exit (GE) modes, is presented. The introduction of a slit in the direction of the detector improves the angular resolution by a factor of two and significantly improves the sensitivity of the technique for the chemical characterization of the buried interfaces. By observing the intensity variations of the Mg Kα and Co Lα characteristic emissions as a function of the incident (GI mode) or detection (GE mode) angle, it is shown that the interfaces of the Si/[Mg/Co/Zr]_×30 multilayer are abrupt, whereas in the Si/[Mg/Zr/Co]_×30 multilayer a strong intermixing occurs at the Co‐on‐Zr interfaces. An explanation of this opposite behavior of the Co‐on‐Zr and Zr‐on‐Co interfaces is given by the calculation of the mixing enthalpies of the Co–Mg, Co–Zr and Mg–Zr systems, which shows that the Co–Zr system presents a negative value and the other two systems present positive values. Together with the difference of the surface free energies of Zr and Co, this leads to the Mg/Zr/Co system being considered as a Mg/Co_xZr_y bi‐layer stack, with x/y estimated around 3.5.     

Characterization of X‐ray gas attenuator plasmas by optical emission and tunable laser absorption spectroscopies

X‐ray gas attenuators are used in high‐energy synchrotron beamlines as high‐pass filters to reduce the incident power on downstream optical elements. The absorption of the X‐ray beam ionizes and heats up the gas, creating plasma around the beam path and hence temperature and density gradients between the center and the walls of the attenuator vessel. The objective of this work is to demonstrate experimentally the generation of plasma by the X‐ray beam and to investigate its spatial distribution by measuring some of its parameters, simultaneously with the X‐ray power absorption. The gases used in this study were argon and krypton between 13 and 530 mbar. The distribution of the 2p excited states of both gases was measured using optical emission spectroscopy, and the density of argon metastable atoms in the 1s₅ state was deduced using tunable laser absorption spectroscopy. The amount of power absorbed was measured using calorimetry and X‐ray transmission. The results showed a plasma confined around the X‐ray beam path, its size determined mainly by the spatial dimensions of the X‐ray beam and not by the absorbed power or the gas pressure. In addition, the X‐ray absorption showed a hot central region at a temperature varying between 400 and 1100 K, depending on the incident beam power and on the gas used. The results show that the plasma generated by the X‐ray beam plays an essential role in the X‐ray absorption. Therefore, plasma processes must be taken into account in the design and modeling of gas attenuators.     

Room‐temperature epitaxial growth of high‐quality m ‐plane InGaN films on ZnO substrates

The authors have grown high‐quality m ‐plane In_0.36Ga_0.64N (1 00) films on ZnO (1 00) substrates at room temperature (RT) by pulsed laser deposition (PLD) and have investigated their structural properties. m ‐plane InGaN films grown on ZnO substrates at RT possess atomically flat surfaces with stepped and terraced structures, indicating that the film growth proceeds in a two‐dimensional mode. X‐ray diffraction measurements have revealed that the m ‐plane InGaN films grow without phase separation reactions at RT. The full‐width at half‐maximum values of the 1 00 X‐ray rocking curves of films with X‐ray incident azimuths perpendicular to the c ‐ and a‐axis are 88 arcsec and 78 arcsec, respectively. Reciprocal space‐mapping has revealed that a 50 nm thick m ‐plane In_0.36Ga_0.64N film grows coherently on the ZnO substrate, which can probably explain the low defect density that is observed in the film. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Quick X‐ray reflectivity using monochromatic synchrotron radiation for time‐resolved applications

A new technique for the parallel collection of X‐ray reflectivity (XRR) data, compatible with monochromatic synchrotron radiation and flat substrates, is described and applied to the in situ observation of thin‐film growth. The method employs a polycapillary X‐ray optic to produce a converging fan of radiation, incident onto a sample surface, and an area detector to simultaneously collect the XRR signal over an angular range matching that of the incident fan. Factors determining the range and instrumental resolution of the technique in reciprocal space, in addition to the signal‐to‐background ratio, are described in detail. This particular implementation records ～5° in 2gθ and resolves Kiessig fringes from samples with layer thicknesses ranging from 3 to 76 nm. The value of this approach is illustrated by showing in situ XRR data obtained with 100 ms time resolution during the growth of epitaxial La_0.7Sr_0.3MnO₃ on SrTiO₃ by pulsed laser deposition at the Cornell High Energy Synchrotron Source (CHESS). Compared with prior methods for parallel XRR data collection, this is the first method that is both sample‐independent and compatible with the highly collimated, monochromatic radiation typical of third‐generation synchrotron sources. Further, this technique can be readily adapted for use with laboratory‐based sources.     

Cascade Mi (i = 1–5) subshell X‐ray emission at incident photon energies across the Lj (j = 1–3) subshell absorption edges of 66Dy

The total M shell and the M_k (k = ξ, αβ, γ, m) X‐ray production cross sections for ₆₆Dy have been measured at incident photon energies across its L_j (j = 1–3) subshell absorption edge energies, ranging 7.8–9.2 keV. This study aims to investigate the evolution of the probability for cascade decay of L_j subshell vacancies as the tunable incident energy ionizes progressively different ₆₆Dy L_j subshells. The experimental X‐ray production cross sections have been compared with theoretical ones calculated using the nonrelativistic Hartree–Fock–Slater (HFS) model‐based photoionization cross sections; three sets of the X‐ray emission rates, fluorescence and Coster–Kronig yield based on the nonrelativistic Hartree–Slater (NRHS) model, Dirac–Hartree–Slater (DHS) model and Dirac–Fock (DF) model; the L_j (j = 1–3) subshell to the M_i (i = 1–5) subshell vacancy transfer probabilities evaluated in the present work. Presently measured total M shell and the M_αβ X‐ray production cross sections are found to be significantly lower than the theoretical ones evaluated using physical parameters based on the relativistic Dirac–Fock/Dirac–Hartree–Slater model calculations, whereas a much better agreement is observed with respect to the NRHS model‐based calculations; however, the measured X‐ray production cross sections are still systematically lower than the NRHS values.     

Extending the quantitative analytical capabilities of the EDXRF technique for plant‐based samples

The energy‐dispersive x‐ray fluorescence (EDXRF) technique has limitations in the quantitative analysis of light elements (low‐Z analytes with Z < 10), for many reasons. This work, however, circumvents the problem through an a priori determination of low‐Z analytes, representative of plant‐based samples. The main purpose of this work was to characterize the major elements in the dark matrix of some plant‐based samples (including biomonitors) using Rutherford backscattering spectrometry (RBS), and the results provided as a generalized input for EDXRF analysis. The derived stoichiometry and mass ratio for the moss, lichen, and cotton cellulose samples analyzed were found to be similar and close to C₇H₁₀O₅, with an average matrix of C = 49.8%, H = 4.0% and O = 45.8%. Quantitative analysis of plant‐based reference material IAEA‐336 (lichen) was subsequently carried out. Use of the a priori determined dark matrix elements (from one‐time RBS spectrometry) extended the scope of applicability of the EDXRF quantitative methods used, and improved accuracy in the elemental analysis of plant‐based samples. The results obtained were in good agreement with the reference values. Copyright © 2004 John Wiley & Sons, Ltd.     

Fluorescence imaging of reactive oxygen species by confocal laser scanning microscopy for track analysis of synchrotron X‐ray photoelectric nanoradiator dose: X‐ray pump–optical probe

Bursts of emissions of low‐energy electrons, including interatomic Coulomb decay electrons and Auger electrons (0–1000 eV), as well as X‐ray fluorescence produced by irradiation of large‐Z element nanoparticles by either X‐ray photons or high‐energy ion beams, is referred to as the nanoradiator effect. In therapeutic applications, this effect can damage pathological tissues that selectively take up the nanoparticles. Herein, a new nanoradiator dosimetry method is presented that uses probes for reactive oxygen species (ROS) incorporated into three‐dimensional gels, on which macrophages containing iron oxide nanoparticles (IONs) are attached. This method, together with site‐specific irradiation of the intracellular nanoparticles from a microbeam of polychromatic synchrotron X‐rays (5–14 keV), measures the range and distribution of OH radicals produced by X‐ray emission or superoxide anions () produced by low‐energy electrons. The measurements are based on confocal laser scanning of the fluorescence of the hydroxyl radical probe 2‐[6‐(4′‐amino)phenoxy‐3H‐xanthen‐3‐on‐9‐yl] benzoic acid (APF) or the superoxide probe hydroethidine‐dihydroethidium (DHE) that was oxidized by each ROS, enabling tracking of the radiation dose emitted by the nanoradiator. In the range 70 µm below the irradiated cell, radicals derived mostly from either incident X‐ray or X‐ray fluorescence of ION nanoradiators are distributed along the line of depth direction in ROS gel. In contrast, derived from secondary electron or low‐energy electron emission by ION nanoradiators are scattered over the ROS gel. ROS fluorescence due to the ION nanoradiators was observed continuously to a depth of 1.5 mm for both oxidized APF and oxidized DHE with relatively large intensity compared with the fluorescence caused by the ROS produced solely by incident primary X‐rays, which was limited to a depth of 600 µm, suggesting dose enhancement as well as more penetration by nanoradiators. In conclusion, the combined use of a synchrotron X‐ray microbeam‐irradiated three‐dimensional ROS gel and confocal laser scanning fluorescence microscopy provides a simple dosimetry method for track analysis of X‐ray photoelectric nanoradiator radiation, suggesting extensive cellular damage with dose‐enhancement beyond a single cell containing IONs.     

Development of variable‐magnification X‐ray Bragg optics

A novel X‐ray Bragg optics is proposed for variable‐magnification of an X‐ray beam. This X‐ray Bragg optics is composed of two magnifiers in a crossed arrangement, and the magnification factor, M, is controlled through the azimuth angle of each magnifier. The basic properties of the X‐ray optics such as the magnification factor, image transformation matrix and intrinsic acceptance angle are described based on the dynamical theory of X‐ray diffraction. The feasibility of the variable‐magnification X‐ray Bragg optics was verified at the vertical‐wiggler beamline BL‐14B of the Photon Factory. For X‐ray Bragg magnifiers, Si(220) crystals with an asymmetric angle of 14° were used. The magnification factor was calculated to be tunable between 0.1 and 10.0 at a wavelength of 0.112 nm. At various magnification factors (M≥ 1.0), X‐ray images of a nylon mesh were observed with an air‐cooled X‐ray CCD camera. Image deformation caused by the optics could be corrected by using a 2 × 2 transformation matrix and bilinear interpolation method. Not only absorption‐contrast but also edge‐contrast due to Fresnel diffraction was observed in the magnified images.     

Element‐specific microtomographic imaging of Drosophila brain stained with high‐Z probes

An application of X‐ray microtomography to the Drosophila adult brain stained with colloidal gold and a platinum compound is described. The transparency of biological tissue to hard X‐rays enables tomographic visualization of the three‐dimensional structure of tissue entrails. Each high‐Z element was visualized as a three‐dimensional structure from the difference absorption coefficient image at the corresponding L_III absorption edge. The cortex of the optic lobe was selectively visualized by the specific adsorption of colloidal gold. The entire structure revealed by the platinum impregnation allowed the anatomical assignment of the gold‐stained structures. Selective staining and specific visualization of biological tissues at micrometer resolution should elucidate the three‐dimensional cellular organization essential for the understanding and application of biological microstructures.     

Measurement of the X‐ray mass attenuation coefficients of silver in the 5–20 keV range

The X‐ray mass attenuation coefficients of silver were measured in the energy range 5–20 keV with an accuracy of 0.01–0.2% on a relative scale down to 5.3 keV, and of 0.09–1.22% on an absolute scale to 5.0 keV. This analysis confirms that with careful choice of foil thickness and careful correction for systematics, especially including harmonic contents at lower energies, the X‐ray attenuation of high‐Z elements can be measured with high accuracy even at low X‐ray energies (<6 keV). This is the first high‐accuracy measurement of X‐ray mass attenuation coefficients of silver in the low energy range, indicating the possibility of obtaining high‐accuracy X‐ray absorption fine structure down to the L₁ edge (3.8 keV) of silver. Comparison of results reported here with an earlier data set optimized for higher energies confirms accuracy to within one standard error of each data set collected and analysed using the principles of the X‐ray extended‐range technique (XERT). Comparison with theory shows a slow divergence towards lower energies in this region away from absorption edges. The methodology developed can be used for the XAFS analysis of compounds and solutions to investigate structural features, bonding and coordination chemistry.     

The investigation of K‐shell fluorescence parameters of Zn–Fe alloys with different grain size and microstrain values

It is known that zinc alloys with iron group metals have better corrosion resistance than pure zinc. Owing to the corrosion resistance of these alloys, Zn–Fe coatings are widely used in automotive industry and have excellent mechanical performance. In this work, we investigated the relationship between the changes in the measured X‐ray fluorescence parameters (K_β/K_α, σ_Kα and σ_Kβ) and the changes in the structural parameters such as microstrain or grain size values for Zn–Fe alloys that were prepared with different pH values. To explain these changes, the K_α and K_βX‐ray production cross sections, and the K_β/K_αX‐ray intensity ratio values were calculated by three different ways for the elemental forms of Zn and Fe. The structural parameters, such as microstrain and grain size, were also calculated. We expect that the outer shell electronic distribution affects the structural parameters of the produced Zn–Fe alloys, changing the measured K_α and K_βX‐ray production cross sections, and the K_β/K_αX‐ray intensity ratio values. We also show that Zn–Fe alloy mi nimum microstrain value corresponds to the maximum changes in K_βX‐ray production cross‐section values of Fe and Zn. Copyright © 2017 John Wiley & Sons, Ltd.     

Influence of photo and Auger electrons of the elements with high atomic numbers on formation of carbon x‐ray fluorescence intensity

The x‐ray fluorescence radiation of carbon was studied in the presence of elements with high atomic numbers in the material irradiated. It was found that photo and Auger electrons of such elements originating from ionization of shells remote from nucleus (L‐, M‐ and N‐shells) effectively excite atoms of carbon. Hence, using a matrix with Z > 30, the influence of the electrons should be considered, and using a matrix with Z > 50 this influence becomes decisive. Calculations of carbon x‐ray fluorescence intensity were executed for different x‐ray tube anodes. Their correctness is confirmed by agreement with experimental results. Copyright © 2005 John Wiley & Sons, Ltd.     

Zr and Ba edge phenomena in the scintillation intensity of fluorozirconate‐based glass‐ceramic X‐ray detectors

The energy‐dependent scintillation intensity of Eu‐doped fluorozirconate glass‐ceramic X‐ray detectors has been investigated in the energy range from 10 to 40 keV. The experiments were performed at the Advanced Photon Source, Argonne National Laboratory, USA. The glass ceramics are based on Eu‐doped fluorozirconate glasses, which were additionally doped with chlorine to initiate the nucleation of BaCl₂ nanocrystals therein. The X‐ray excited scintillation is mainly due to the 5d–4f transition of Eu²⁺ embedded in the BaCl₂ nanocrystals; Eu²⁺ in the glass does not luminesce. Upon appropriate annealing the nanocrystals grow and undergo a phase transition from a hexagonal to an orthorhombic phase of BaCl₂. The scintillation intensity is investigated as a function of the X‐ray energy, particle size and structure of the embedded nanocrystals. The scintillation intensity versus X‐ray energy dependence shows that the intensity is inversely proportional to the photoelectric absorption of the material, i.e. the more photoelectric absorption the less scintillation. At 18 and 37.4 keV a significant decrease in the scintillation intensity can be observed; this energy corresponds to the K‐edge of Zr and Ba, respectively. The glass matrix as well as the structure and size of the embedded nanocrystals have an influence on the scintillation properties of the glass ceramics.