Photoelectric Cross Sections Research Articles

Impact of new ICRU Report 90 recommendations on calculated correction factors for reference dosimetry

In 2016 the ICRU published a new report dealing with key data for ionizing radiation dosimetry (ICRU Report 90). New recommendations have been made for the mean excitation energies I for air, graphite and liquid water as well as for the graphite density to use when evaluating the density effect. In addition, the ICRU Report 90 discusses renormalized photoelectric cross sections, but refuses to give a recommendation on the use of renormalization factors. However, the Consultative Committee for Ionizing Radiation recommends to use renormalized photoeffect cross sections. Goal of the present work is to evaluate the impact of these new recommendations on clinical reference dosimetry for high energy photon and electron beams.The beam quality correction factor kQ was calculated by Monte Carlo simulations for compact and parallel plate ionization chambers. In case of photons seven phase space files from clinical accelerators and twelve spectra taken from literature from 4 MV to 24 MV and additionally a 60Co source were applied. As electron source thirteen electron spectra available in literature were used in the range of 4 MeV–21 MeV.The new ICRU recommendations have a small impact on Monte Carlo calculated kQ values for the chosen ionization chambers in the range of 0.1%–0.35% only—the difference increases for higher photon energies.The impact of the ICRU Report 90 recommendations on Monte Carlo calculated stopping power ratios sw,a, perturbation factors p and beam quality correction factors kQ was investigated and confirmed a decrese of sw,a by a fraction of a percent for photon and electron beams. This study indicates that the impact of the new ICRU recommendation is within 0.35%. The determined deviations should be taken into account, when widely published Monte Carlo calculated values are examined.

Abstract 670: Specific ROS generation and monitoring in cancer using radioactive gold nanoparticle

Abstract Radiotherapy is a key treatment and is beneficial in the treatment of about 50% of all cancer patients. Such treatment relies on the deposition of energy (the dose) in tumour cells, typically by irradiation with either high-energy gamma rays or X-rays (photons), or energetic beams of ions, sufficient to damage the cancer cells or their vasculature and thus induce tumour death or nutrient starvation. However, like chemotherapy, photon radiotherapy is non-specific, since a significant dose can be delivered to healthy tissue along the track of the photons, in front and behind the tumour. Therefore, recently several research groups have proposed the use of specifically targeted noble-metal nanoparticles irradiated by radiation as an effective therapeutic tool for treating various malignancies with minimum collateral damage to healthy tissue. In general, the photoelectric absorption cross sections of radiosensitive materials directly depend on atom radius, and thus their radiotherapy effects also depend on atom radius. This physical principle determines that gold (atomic-number Z=79) has a stronger radiation enhancement effect by photoelectric effect. Loading with gold nanoparticles (AuNPs) is one of the promising candidates in this area. Gold NPs have a larger atomic radius than gold atom (~0.17 nm), and thus should have a stronger radiation enhancement effect than gold atom. During irradiation, this results in an enhancement of the energy deposition in the vicinity of the gold particles generate the ROS on the surface due to the generation of photoelectrons, Auger electrons, and characteristic X-rays. ROS play important roles in various cellular process. In particularly, at sufficiently high concentrations, ROS could become an effect that is utilized for various therapeutic application such as apoptosis. Herein, we synthesized the radiosensitizer PEGylated gold nanoparticles (RPAuNPs) for generation and measuring of ROS on surface by radiation exposure. First, gold nanoparticles (AuNPs) was prepared by one-pot synthesis and the sharpness and size were efficiently controlled by adjusting the amount of reducing agent. Furthermore, they were replaced with heterobifunctional PEG (COOH-PEG-SH) not only to serve as a biocompatible stabilizer (PAuNPs) and but also to conjugate Dihydrorhodamine 123 (DHR 123) (RPAuNPs) as ROS sensor. Well-engineered formation of RPAuNPs was verified by transmission electron microscopy (TEM) showing their overall size of 50 nm. In addition, UV-Vis data strongly demonstrated successful synthesis. We evaluated their functional use in inducing ROS and the results showed that our radiosensitizing agents exhibited the feasibility of effective ROS generation under x-ray radiation. And we investigated there in vitro/in vivo imaging and therapeutic efficacies, optical properties, biocompatibility for tumor cell. Citation Format: Jihye Choi, Yoon Woo Koh, Hyung Kwon Byeon, Guillem Pratx, Jaemoon Yang. Specific ROS generation and monitoring in cancer using radioactive gold nanoparticle [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 670.

Monte Carlo studies on photon interactions in radiobiological experiments.

X-ray and γ-ray photons have been widely used for studying radiobiological effects of ionizing radiations. Photons are indirectly ionizing radiations so they need to set in motion electrons (which are a directly ionizing radiation) to perform the ionizations. When the photon dose decreases to below a certain limit, the number of electrons set in motion will become so small that not all cells in an “exposed” cell population can get at least one electron hit. When some cells in a cell population are not hit by a directly ionizing radiation (in other words not irradiated), there will be rescue effect between the irradiated cells and non-irradiated cells, and the resultant radiobiological effect observed for the “exposed” cell population will be different. In the present paper, the mechanisms underlying photon interactions in radiobiological experiments were studied using our developed NRUphoton computer code, which was benchmarked against the MCNP5 code by comparing the photon dose delivered to the cell layer underneath the water medium. The following conclusions were reached: (1) The interaction fractions decreased in the following order: 16O > 12C > 14N > 1H. Bulges in the interaction fractions (versus water medium thickness) were observed, which reflected changes in the energies of the propagating photons due to traversals of different amount of water medium as well as changes in the energy-dependent photon interaction cross-sections. (2) Photoelectric interaction and incoherent scattering dominated for lower-energy (10 keV) and high-energy (100 keV and 1 MeV) incident photons. (3) The fractions of electron ejection from different nuclei were mainly governed by the photoelectric effect cross-sections, and the fractions from the 1s subshell were the largest. (4) The penetration fractions in general decreased with increasing medium thickness, and increased with increasing incident photon energy, the latter being explained by the corresponding reduction in interaction cross-sections. (5) The areas under the angular distribution curves of photons exiting the medium layer and subsequently undergoing interactions within the cell layer became smaller for larger incident photon energies. (6) The number of cells suffering at least one electron hit increased with the administered dose. For larger incident photon energies, the numbers of cells suffering at least one electron hit became smaller, which was attributed to the reduction in the photon interaction cross-section. These results highlighted the importance of the administered dose in radiobiological experiments. In particular, the threshold administered doses at which all cells in the exposed cell array suffered at least one electron hit might provide hints on explaining the intriguing observation that radiation-induced cancers can be statistically detected only above the threshold value of ~100 mSv, and thus on reconciling controversies over the linear no-threshold model.

Duvernay shale lithofacies distribution analysis in the West Canadian Sedimentary Basin

In the West Canadian Sedimentary Basin (WCSB), Duvernay shale is considered to contribute most of the Canadian shale gas reserve and production. According to global shale gas exploration and development practice, reservoir property and well completion quality are the two key factors determining the shale gas economics. The two key factors are strongly depending on shale lithofacies. On the basis of inorganic mineralogy theory, all available thin section, X-ray diffraction, scanning electron microscope (SEM), energy dispersive spectrometer (EDS) data were used to assist lithofacies analysis. Gamma ray (GR), acoustic (AC), bulk density (RHOB), neutron porosity (NPHI) and photoelectric absorption cross-section index (PE) were selected for log response analysis of various minerals. Reservoir representative equation was created constrained by quantitative core analysis results, and matrix mineral percentage of quartz, carbonate, feldspar and pyrite were calculated to classify shale lithofacies. Considering the horizontal continuity of seismic data, rock physics model was built, and acoustic impedance integrated with core data and log data was used to predict the horizontal distribution of different lithofacies. The results indicate that: (1) nine lithofacies can be categorized in Duvernay shale, (2) the horizontal distribution of different lithofacies is quite diversified, siliceous shale mainly occurs in Simonette area, calcareous shale is prone to develop in the vicinity of reef, while calcareous-siliceous shale dominates in Willesdon Green area.

Energy-angle correlation correction algorithm for monochromatic computed tomography based on Thomson scattering X-ray source

The necessity for compact and relatively low cost x-ray sources with monochromaticity, continuous tunability of x-ray energy, high spatial coherence, straightforward polarization control, and high brightness has led to the rapid development of Thomson scattering x-ray sources. To meet the requirement of in-situ monochromatic computed tomography (CT) for large-scale and/or high-attenuation materials based on this type of x-ray source, there is an increasing demand for effective algorithms to correct the energy-angle correlation. In this paper, we take advantage of the parametrization of the x-ray attenuation coefficient to resolve this problem. The linear attenuation coefficient of a material can be decomposed into a linear combination of the energy-dependent photoelectric and Compton cross-sections in the keV energy regime without K-edge discontinuities, and the line integrals of the decomposition coefficients of the above two parts can be determined by performing two spectrally different measurements. After that, the line integral of the linear attenuation coefficient of an imaging object at a certain interested energy can be derived through the above parametrization formula, and monochromatic CT can be reconstructed at this energy using traditional reconstruction methods, e.g., filtered back projection or algebraic reconstruction technique. Not only can monochromatic CT be realized, but also the distributions of the effective atomic number and electron density of the imaging object can be retrieved at the expense of dual-energy CT scan. Simulation results validate our proposal and will be shown in this paper. Our results will further expand the scope of application for Thomson scattering x-ray sources.

MCNP6.1 simulations for low-energy atomic relaxation: Code-to-code comparison with GATEv7.2, PENELOPE2014, and EGSnrc

Abstract Emerging radiological applications of gold nanoparticles demand low-energy electron/photon transport calculations including details of an atomic relaxation process. Recently, MCNP® version 6.1 (MCNP6.1) has been released with extended cross-sections for low-energy electron/photon, subshell photoelectric cross-sections, and more detailed atomic relaxation data than the previous versions. With this new feature, the atomic relaxation process of MCNP6.1 has not been fully tested yet with its new physics library (eprdata12) that is based on the Evaluated Atomic Data Library (EADL). In this study, MCNP6.1 was compared with GATEv7.2, PENELOPE2014, and EGSnrc that have been often used to simulate low-energy atomic relaxation processes. The simulations were performed to acquire both photon and electron spectra produced by interactions of 15 keV electrons or photons with a 10-nm-thick gold nano-slab. The photon-induced fluorescence X-rays from MCNP6.1 fairly agreed with those from GATEv7.2 and PENELOPE2014, while the electron-induced fluorescence X-rays of the four codes showed more or less discrepancies. A coincidence was observed in the photon-induced Auger electrons simulated by MCNP6.1 and GATEv7.2. A recent release of MCNP6.1 with eprdata12 can be used to simulate the photon-induced atomic relaxation.

Sedimentary control on the formation of a multi-superimposed gas system in the development of key layers in the sequence framework

Based on core observations, well logs and test results of siderite-bearing mudstone from the Benxi Formation to the Member 2 of the Shanxi Formations in the Linxing block, northeastern Ordos Basin, a logging identification model for siderite-bearing mudstone (key layer) was established. The porosity characteristics and sealing property were quantitatively evaluated by logging data. Sedimentary control on the formation of multi-superimposed gas-bearing system in the development of key layers in the sequence framework was also discussed. The results showed that the siderite-bearing mudstone has obvious logging response characteristics, e.g., high photoelectric absorption cross-section index (PE), high density (DEN), high amplitude natural gamma ray (GR), low acoustic (AC), low resistivity (M2RX) and low neutron porosity (CNCF). The quantitatively evaluated results of the porosity characteristics and sealing property for the key layer showed that the key layer has the characteristics of low porosity (with an average of 1.20 percent), low permeability (with an average of 2.29 × 10−8μm2), and high breakthrough pressure (with an average of 12.32 MPa) in the study area. This layer acts as an impermeable gas barrier in a multi-superimposed gas system. The results also indicated that the material composition of the multi-superimposed gas-bearing system can be established by the sequence stratigraphic framework. The sedimentary evolution results in a cyclic rhythm of material composition vertically. The spatial distribution of the corresponding transgressive event layer near the maximum flooding surface (MFS) in the sequence framework restricts the spatial distribution of the key layer with high breakthrough pressure and low porosity, which constitutes the gas-bearing system boundary. The siderite-bearing mudstone formed near the MFS in the second-order sequence and constitutes a stable comparison of the first-order gas-bearing system boundary, which has a wide range of regional distribution and stable thickness. The siderite-bearing mudstone formed near the MFS in the third-order sequence is often incompletely preserved due to the late (underwater) diversion channel erosion and cutting. This layer forms the coal-bearing reservoirs, which we termed as a second-order gas-bearing system in adjacent third-order sequences to form a uniform gas-bearing system.

Extraction of the Proton and Electron Radii from Characteristic Atomic Lines and Entropy Principles

We determine the proton and electron radii by analyzing constructive resonances at minimum entropy for elements with atomic number Z ≥ 11.We note that those radii can be derived from entropy principles and published photoelectric cross sections data from the National Institute of Standards and Technology (NIST). A resonance region with optimal constructive interference is given by a principal wavelength λ of the order of Bohr atom radius. Our study shows that the proton radius deviations can be measured. Moreover, in the case of the electron, its radius converges to electron classical radius with a value of 2.817 fm. Resonance waves afforded us the possibility to measure the proton and electron radii through an interference term. This term, was a necessary condition in order to have an effective cross section maximum at the threshold. The minimum entropy means minimum proton shape deformation and it was found to be (0.830 ± 0.015) fm and the average proton radius was found to be (0.825 − 0.0341; 0.888 + 0.0405) fm.

Determination of LIIIsubshell photoelectric parameters of iridium

The LIIIsubshell photoelectric cross section, jump ratio, jump factor, and Davisson–Kirchner ratio of iridium have been determined by mass attenuation coefficients. The measurements have been performed using the X-ray attenuation method in narrow beam geometry. The obtained results have been compared with the tabulated values of XCOM (Berger et al. XCOM: Photon cross section database (version 1.3). NIST. Available at http://physics.nist.gov/xcom . 2005) and FFAST (Chantler et al. X-ray form factor, attenuation and scattering tables (version 2.1). NIST. Available at http://physics.nist.gov/ffast . 2005).

Effective X-ray beam size measurements of an X-ray tube and polycapillary X-ray lens system using a scanning X-ray fluorescence method

Size measurements of an X-ray beam produced by an integrated polycapillary X-ray lens (PXL) and X-ray tube system were performed by means of a scanning X-ray fluorescence (SXRF) method using three different metallic wires. The beam size was obtained by fitting the SXRF data with the analytical convolution between a Gaussian and a constant functions. For each chemical element in the wire an effective energy was calculated based on the incident X-ray spectrum and its photoelectric cross section. The proposed method can be used to measure the effective X-ray beam size in XRF microscopy studies.

Preliminary Study of Double Beta Decay: Simulation of CaMoO4 Scintillation Detector Response Function to the Gamma Ray Radiation

<p class="TTPAbstract">CaMoO<sub>4</sub> crystal is a material candidate forthe scintillation detector and double beta decay experiment to determinea neutrino mass. The objective of this work is to analyze the response function of CaMoO<sub>4 </sub>using Monte Carlo GEANT4 simulation. Penelope-low energy method was used as an interaction type for the electromagnetic process. The simulation results show that the presence of the photopeak energies of gamma ray from Cs-137, Co-60 and K-40 sources can be identified and observed in the energy 0.662 MeV, 1.17 MeV, 1.33 MeV and 1.5 MeV. The photoelectric cross section interaction of CaMoO<sub>4 </sub>is lower than NaI(Tl), but in other hand the incoherent cross section is vice versa.</p>

Preliminary Study of Double Beta Decay: Simulation of CaMoO4 Scintillation Detector Response Function to the Gamma Ray Radiation

<p class="TTPAbstract">CaMoO<sub>4</sub> crystal is a material candidate forthe scintillation detector and double beta decay experiment to determinea neutrino mass. The objective of this work is to analyze the response function of CaMoO<sub>4 </sub>using Monte Carlo GEANT4 simulation. Penelope-low energy method was used as an interaction type for the electromagnetic process. The simulation results show that the presence of the photopeak energies of gamma ray from Cs-137, Co-60 and K-40 sources can be identified and observed in the energy 0.662 MeV, 1.17 MeV, 1.33 MeV and 1.5 MeV. The photoelectric cross section interaction of CaMoO<sub>4 </sub>is lower than NaI(Tl), but in other hand the incoherent cross section is vice versa.</p>

On a new mechanism on [formula omitted]-ray attenuation strengthened by new data

Introduction We extended our previous detailed γ -ray attenuation measurements of 60Co γ rays in Pb and Fe to include also Cu, Hg, Al and H2O. Purpose To introduce a new mechanism on γ -ray attenuation in matter. Materials and methods 60Co radiation source, slices of the absorbers and a Geiger Muller detector counter in broad and thin beam geometries. Experiments We performed detailed measurements of the detected radiation versus the thickness of the absorber and in parallel Monte Carlo simulations for each experiment. Results Monte-Carlo calculations were in qualitative agreement with experiment but quantitatively predicted systematically more radiation at the target. We related the differences with the parameters Eγ and Zeff of the photoelectric absorption cross section which guided us to propose a new mechanism on the absorption of γ rays in matter. The γ radiation creates a huge number of electrons and ions passing through the absorber which form a steady state plasma condition increasing slightly the parameters Eb and Zeff of the lattice which in turn can increase measurably the photoelectric absorption thus restoring the agreement between Monte Carlo calculations and experiment. Conclusion Based on our large set of data which included absorbers in a wide range of Zeff we strengthened the need for a new mechanism on γ-ray absorption in matter.

Contribution of inner shell Compton ionization to the X-ray fluorescence line intensity

The Compton effect is a potential ionization mechanism of atoms. It produces vacancies in inner shells that are filled with the same mechanism of atomic relaxation as the one following photo-absorption. This contribution to X-ray fluorescence emission is frequently neglected because the total Compton cross-section is apparently much lower than the photoelectric one at useful X-ray energies. However, a more careful analysis suggests that is necessary to consider single shell cross sections (instead of total cross sections) as a function of energy. In this article these Compton cross sections are computed for the shells K, L1-L3 and M1-M5 in the framework of the impulse approximation. By comparing the Compton and the photoelectric cross-section for each shell it is then possible to determine the extent of the Compton correction to the intensity of the corresponding characteristic lines. It is shown that for the K shell the correction becomes relevant for excitation energies which are too high to be influent in X-ray spectrometry. In contrast, for L and M shells the Compton contribution is relevant for medium-Z elements and medium energies. To illustrate the different grades of relevance of the correction, for each ionized shell, the energies for which the Compton contribution reaches the extent levels of 1, 5, 10, 20, 50 and 100% of the photoelectric one are determined for all the elements with Z=11–92. For practical applications it is provided a simple formula and fitting coefficients to compute average correction levels for the shells considered.

Chemical effect on the K shell absorption parameters of some selected cerium compounds

In this study, the photoelectric cross section values of Ce, CeCl3.7H2O, Ce2(SO4)3, Ce(OH)4 and Ce2O3 samples were measured in the energy range from 31.82 keV up to 51.70 keV by adopting in narrow beam geometry. Using these photoelectric cross sections, the K shell photoelectric cross sections at the K-edge, the K shell absorption jump ratios and jump factors, the Davisson-Kirchner ratios and K shell oscillator strength values were estimated experimentally. The measured parameters were compared with the theoretical calculated values. It is observed that the K shell photoelectric cross section at the K-edge and K shell oscillator strength values of an element are affected by the chemical environment of material while the K shell absorption jump ratio, K shell absorption jump factor and Davisson-Kirchner ratio are not affected by the chemical environment of material for the present samples. To the best of our knowledge, the chemical effects on the Davisson-Kirchner ratio and K shell oscillator strength have not been discussed for any element by now.

An advanced ionizing radiation monitoring network based on using SrI2(Eu)/MPPC module

An advanced ionizing radiation monitoring network (AIRMN) system using a single‐crystal SrI2(Eu) scintillator has been developed. The SrI2(Eu)‐scintillator (25 mmφ × 25 mm) has excellent material properties, including a high light yield (>80 000 photons/MeV), a high photoelectric cross section, and high energy resolution (<4%). The system has a multi‐pixel photon counter as a light detector. The resolution and sensitivity of the new AIRMN allow the radioactive Cs originating from the Fukushima Daiichi Nuclear Power Plant accident to be distinguished from other radioactive species, leading to the precise assessment of the ambient dose originating from 134Cs and 137Cs radiation. Furthermore, a software platform is described that is adopted in the AIRMN and based on the use of the ANSI N42‐42 Data File Format published by the National Institute of Standards and Technology. It allows for the standardization of ionizing radiation monitoring. Copyright © 2016 John Wiley & Sons, Ltd.

Advanced multimodal nanoparticles delay tumor progression with clinical radiation therapy

Radiation therapy is a major treatment regimen for more than 50% of cancer patients. The collateral damage induced on healthy tissues during radiation and the minimal therapeutic effect on the organ-of-interest (target) is a major clinical concern. Ultra-small, renal clearable, silica based gadolinium chelated nanoparticles (SiGdNP) provide simultaneous MR contrast and radiation dose enhancement. The high atomic number of gadolinium provides a large photoelectric cross-section for increased photon interaction, even for high-energy clinical radiation beams. Imaging and therapy functionality of SiGdNP were tested in cynomolgus monkeys and pancreatic tumor-bearing mice models, respectively. A significant improvement in tumor cell damage (double strand DNA breaks), growth suppression, and overall survival under clinical radiation therapy conditions were observed in a human pancreatic xenograft model. For the first time, safe systemic administration and systematic renal clearance was demonstrated in both tested species. These findings strongly support the translational potential of SiGdNP for MR-guided radiation therapy in cancer treatment.

SU‐G‐TeP3‐13: The Role of Nanoscale Energy Deposition in the Development of Gold Nanoparticle‐Enhanced Radiotherapy

Purpose:Gold nanoparticles (GNPs) can enhance radiotherapy effects. The high photoelectric cross section of gold relative to tissue, particularly at lower energies, leads to localized dose enhancement. However in a clinical context, photon energies must also be sufficient to reach a target volume at a given depth. These properties must be balanced to optimize such a therapy. Given that nanoscale energy deposition patterns around GNPs play a role in determining biological outcomes, in this work we seek to establish their role in this optimization process.Methods:The PENELOPE Monte Carlo code was used to generate spherical dose deposition kernels in 1000 nm diameter spheres around 50 nm diameter GNPs in response to monoenergetic photons incident on the GNP. Induced “lesions” were estimated by either a local effect model (LEM) or a mean dose model (MDM). The ratio of these estimates was examined for a range of photon energies (10 keV to 2 MeV), for three sets of linear‐quadratic parameters.Results:The models produce distinct differences in expected lesion values, the lower the alpha‐beta ratio, the greater the difference. The ratio of expected lesion values remained constant within 5% for energies of 40 keV and above across all parameter sets and rose to a difference of 35% for lower energies only for the lowest alpha‐beta ratio.Conclusion:Consistent with other work, these calculations suggest nanoscale energy deposition patterns matter in predicting biological response to GNP‐enhanced radiotherapy. However the ratio of expected lesions between the different models is largely independent of energy, indicating that GNP‐enhanced radiotherapy scenarios can be optimized in photon energy without consideration of the nanoscale patterns. Special attention may be warranted for energies of 20 keV or below and low alpha‐beta ratios.

Accurate X-ray Absorption Spectra of Dilute Systems: Absolute Measurements and Structural Analysis of Ferrocene and Decamethylferrocene

X-ray absorption fine structure (XAFS) of ferrocene (Fc) and Decamethylferrocene (DmFc) have been determined on an absolute scale using transmission measurements of multiple solutions of differing concentrations (15 mM, 3 mM, pure solvent) at operating temperatures of 10–20 K. Mass attenuation coefficients and photoelectric absorption cross sections are measured and tabulated for both molecules for an extended energy range in excess of 1.5 keV from the Fe K-shell absorption edge. At these temperatures, the minimization of of dynamic disorder has enabled a critical determination of the oscillatory absorption structures created by multiple-scattering paths of the excited photoelectron. These oscillatory structures are highly sensitive to the local conformation environment of the iron absorber in organometallic structures. Crystallographic and scattering studies have reported both structures characterized by staggered cyclopentadienyl rings, in contrast with low temperature crystallography and recent density functional theoretical predictions. Phase changes in the crystallographic space groups are reported for Fc at different temperatures, raising the possibility of alternative conformation states. Robust experimental techniques are described which have allowed the measurement of XAFS spectra of dilute systems by transmission at accuracies ranging from 0.2% to 2%, and observe statistically significant fine structure at photoelectron wavenumbers extending to >12 Å–1. The subtle signatures of the conformations are then investigated via extensive analysis of the XAFS spectra using the full multiple scattering theory as implemented by the FEFF package. Results indicate a near-eclipsed D5h geometry for low-temperature Fc, in contrast with a staggered D5d geometry observed for DmFc. The ability of this experimental approach and data analysis methodology combined with advanced theory to investigate and observe such subtle conformational differences using XAFS is a powerful tool for future challenges and widens the capacity of advanced XAFS to solve a broad range of challenging systems.

Measurement of Lα and Lβ1,3,4 fluorescence cross sections of La, Ce, Pr and Nd induced by photons of energies between 7.01 keV and 8.75 keV

Abstract This study presents measurement results of x-ray production cross sections of L α and L β1,3,4 emitted by four lanthanoid elements (La, Ce, Pr and Nd), after irradiation with K α and K β X rays of the elements Co, Ni, Cu, and Zn (covering energies between 7.01 keV and 8.75 keV). Primary x-rays were induced in turn by the irradiation of thick targets of these elements with a beam of x-rays produced by a tube with an Rh anode, operating at 50 kV and 850 μA. The experimental results are compared with theoretical cross sections predicted using known tabulations of photoelectric cross sections. Dirac-Hartree-Slater (DHS) atomic parameters were used for these calculations. An acceptable match between experiment and both sets of tabulated data is found.