Atomic Cross Sections Research Articles

Response function and photon interaction of LaBr3:Ce and BGO scintillation detectors by Monte Carlo simulation

This work aims to investigate the response function and photon interaction of the LaBr3:Ce and BGO scintillation detectors using the FLUKA Monte Carlo simulation software. To improve the realism of detectors, the DETGEB card was used to activate the gaussian energy broadening (GEB) function. The GEB parameters of both detectors were obtained by fitting a nonlinear curve to the relation between FWHM and gamma-ray energy. The energy resolution (R), peak-to-Compton ratio (PCR), peak-to-total ratio (PTR), and full-energy peak efficiency (FEPE) of both detectors were investigated by simulation and experiment at different gamma-ray energy obtained from 133Ba, 137Cs, and 60Co sources. The simulated spectra of those radioisotopes were found to agree with the actual spectra. The results found that the R, PCR, and FEPE values of the LaBr3:Ce and BGO detectors tend to decrease as energy increases. Moreover, the total atomic cross-section (σt,a), effective atomic number (Zeff) and effective electron density (Neff) of both crystals was investigated by FLUKA and compared with the XCOM theoretical program covering an energy range of 15 keV to 15 MeV. The simulated results of the σt,a, Zeff, and Neff are in excellent agreement with the theoretical ones. The GEB parameters obtained from this study will improve the simulation performance of LaBr3:Ce and BGO detectors in investigating the gamma-ray response and shielding properties of materials.

A comprehensive analysis on radiation shielding characteristics of borogypsum (boron waste) by Phy-X/PSD code

In the present study, radiation shielding characteristics of the borogypsum, which is a waste generated during the boric acid production in Turkey, was analyzed. For this purpose, we used recently developed Phy-X/PSD software, which is provided to calculate shielding parameters such as mass attenuation coefficient, linear attenuation coefficient, half-value layer, tenth-value layer, effective atomic number, total atomic cross section, total electronic cross section, effective conductivity, effective electron number, buildup factors and fast neutron removal cross section in a wide photon energy range. Additionally, mass attenuation coefficients of borogypsum were compared with those of other radiation shielding materials (ordinary concrete, obsidian, pumice, clay) in order to give a significant evaluation about the radiation shielding capability of borogypsum. Half value layer and fast neutron removal cross section values are also evaluated by other materials. It is noticed that borogypsum has higher shielding potential than other reported shielding materials.

Radiation protection efficiency of newly produced W-based alloys: Experimental and computational study

Tungsten based alloy is one of the materials which has great attention and can be used as gamma-ray shields, radiation source collimator, spallation neutron source target, plasma facing materials, etc. The motivation of the study is to produce new tungsten based alloys and determine the radiation protection characteristics of the alloys that can be used for radiation related applications. In this context, five tungsten based alloys (WxTayCr10Ni10Fe10Mo10) were produced and the dependence of radiation shielding ability on the changes in W and Ta concentration was investigated. The photon protection parameters such as linear attenuation coefficients, mass attenuation coefficients, effective atomic number, mean free path, half-value layer, exposure and energy absorption buildup factors, effective conductivity, effective electron number, atomic and electronic cross sections, and fast neutron removal cross-sections of the alloys were determined by Phy-X/PSD code. Additionally, XRD, EPR and SEM-EDS experimental results were evaluated for the investigation of spectroscopic characteristics. The crystallite sizes of the alloys were calculated by Debye-Scherrer method depending on the XRD phases in order to perform the structural characterization. It is concluded that a relationship exists between the crystallite size and photon attenuation. It may be stated that the increase in the amount of W improves the gamma radiation protection efficiency of the alloys. It is also seen that the fast neutron attenuation feature increases proportionally with W content. It is determined that the tungsten based alloys can be used as good radiation protection materials in radiation related applications.

The Dependence of X-Ray Attenuation Parameters of (Al, Cu, And Zr) Metals on their Atomic Number

This paper studied X-ray attenuation in metals (Al-13, Cu-29, Zr-40). X-ray energy of 17 keV of kα line of molybdenum was directed to metal bars with 0.05 cm thickness. These three metals have differences in their atomic numbers and electronic distributions in the electronic shells; aluminium (Al-13) was chosen as the low atomic number, copper (Cu-29), and zirconium (Zr-40) as the high atomic number. The linear and mass attenuation coefficients, atomic and electronic cross-sections, and electron density for X-ray attenuation through each element were determined experimentally. The results explained a new idea to describe X-ray scattering: the effect of valance and bound electron (electron distribution) of the metals. The metal with more bound electrons in its outermost shell scattered more radiation for a specific range of energy, even though the metal has a less atomic number.

Photodissociation and photoionization of molecules of astronomical interest

Context. Vacuum-ultraviolet (VUV) photons are important drivers of chemical processes in space. Thus, it is important to accurately characterize and constrain photorates in different radiation fields, via the photodissociation and photoionization cross sections of individual atoms and molecules. These have been available in the Leiden VUV photodissocation and photoionization cross section database. Aims. Experimental and theoretical advances in the past decade or so have allowed multiple new cross sections to be obtained, particularly photoionization cross sections of radicals. The database is hereby updated by including these more recent cross sections and is also expanded with several astronomically relevant species. Methods. The cross sections have been used to calculate photodissociation and photoionization rates in several different radiation fields as well as from cosmic-ray-induced VUV fluxes. The reduction of rates in shielded regions was calculated as a function of dust, molecular and atomic hydrogen, atomic carbon, and self-shielding column densities. The relative importance of these shielding types is molecule and atom dependent, as well as the assumed dust absorbance. All the data are publicly available from the Leiden VUV cross section database. Results. The Leiden VUV cross section database has been updated with 14 new astrophysically relevant molecular species and 16 updates to previous entries. The database update is accompanied by a brief review of the basic physical processes, particularly photoionization processes which have not been reviewed in the context of previous database updates.

Dielectric function and band gap determination of single crystal CuFeS2 using FTIR-VIS-UV spectroscopic ellipsometry

Spectroscopic ellipsometry measurements were performed on antiferromagnetic semiconductor CuFeS2 grown via molecular beam epitaxy. UV/Visible and IR ellipsometry data was merged and modeled to derive the dielectric function of CuFeS2 from 30 meV to 4.5 eV. The CuFeS2 samples were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and cross-section scanning electron microscopy (SEM) which gave the crystal quality, surface roughness and sample film thickness. A critical point analysis revealed a direct band gap of 0.76 eV, while modeling gives a carrier concentration of 8 ± 2 × 1019~cm−3 and an estimate of the indirect band gap of 0.5 eV. Optically active infrared phonons were observed at 319 cm−1 and 350 cm−1 with significant Raman active modes at 85.8 cm−1, 265 cm−1, 288 cm−1, 318 cm−1 and 377 cm−1. The fitted optical constants were then used to characterize the crystal quality and spatial uniformity.

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.

Photoionization of C60 at high energies

Calculations of the photoionization cross section of C60 including all valence and core subshells have been carried out for photon energies up to 1 keV using density functional theory (DFT) and time-dependent DFT (TDDFT) within the framework of a fully molecular model. The high-energy valence subshell cross sections behave rather differently than the results from model potentials where the cross section falls far too rapidly with energy. This unphysical behavior of the model calculations is traced to smearing out of the carbon nuclei in the model potentials which makes it difficult for momentum to be conserved at the higher energies. Comparison with 60 times carbon atomic cross section sheds light on similarities and differences. The high energy behavior of individual valence cross sections reflects the amount of C 2s/2p mixing in the molecular orbitals.

Composite cellulose/Fe3O4/Cu for effective X-ray radiation shielding

In this study, a cellulose/Fe3O4/Cu composite was synthesized by the blending method and applied as an X-ray radiation apron. The content of Fe3O4 in each sample was 94 wt%, and the varying levels of cellulose and Cu were 1, 2, 3, 4, and 5 wt%. The crystal phase formed in the sample was observed using X-ray diffraction, and the functional group formed was examined using Fourier transform infrared spectroscopy. The performance of the sample as a radiation shield was analyzed using X-ray mobile with energies of 50, 60, 70, 81, and 90 keV at 10 mAs applied to the sample. The results showed that the samples with composition of 2 wt% cellulose and 4 wt% Cu exhibited the best values for the average size of the smallest crystallite size (12.21 nm), low transmittance, linear attenuation coefficient (μ), mass attenuation coefficient (μm), atomic cross-section (σa), electronic cross-section (σel), half value layer, and mean free path. Alterations observed on the surface of the composite material suggested the impact of incorporating metallic components into nonmetallic constituents. Surface analysis was conducted using scanning electron microscope and revealed that the surface model resembled Brassica oleracea. This feature is advantageous due to the large surface area and absorbent properties associated with such leaves.

Obrazovanie i raspad avtoionizatsionnykh sostoyaniy - osnovnoy mekhanizm neuprugikh poter' pri stolknoveniyakh atomov keV-energiy

It has been shown that the formation of autoionization states makes the dominant contribution to inelastic energy loss and to ionization in keV atomic collisions, i.e., at velocities lower than the velocities of atomic electrons. Scaling laws have been proposed to calculate the cross sections for the formation of vacancies in inner K and L electron shells of colliding atoms. A model has been proposed to relate ionization processes and the observed inelastic energy losses. Auger transitions in a short-lived quasimolecule formed by two atoms approaching each other have been studied. The nature of the continuous component in electron spectra emitted in collisions has been determined. It has been shown that the excitation of autoionization states determines the stopping cross sections for keV atoms in matter.

Cross-calibration of atomic pressure sensors and deviation from quantum diffractive collision universality for light particles

The room-temperature, velocity-averaged, total cross section for atom–atom and atom–molecule collisions can be approximated using a universal function depending only on the magnitude of the leading order dispersion coefficient, C 6. This feature of the total cross section together with the universal function for the energy distribution transferred by glancing angle collisions ( (Booth et al 2019 New J. Phys. 21 102001)) can be used to empirically determine the total collision cross section and realize a self-calibrating, vacuum pressure standard. This was previously validated for Rb+N2 and Rb+Rb collisions. However, the post-collision energy distribution is expected to deviate from in the limit of small C 6 and small reduced mass. Here we observe this deviation experimentally by performing a direct cross-species loss rate comparison for Rb+H2 and Li+H2 collisions. We measure a velocity averaged total collision cross section ratio of . Based on an ab initio computation of m3 s−1, we deduce m3 s−1, in agreement with a Rb+H2 ab initio value of . By contrast, fitting the Rb+H2 loss rate as a function of trap depth to the universal function we find m3 s−1. This work demonstrates the utility of sensor-atom cross-calibration experiments to check the validity of theoretical computations to extend and enhance the performance of cold atom based pressure sensors.

Gamma-ray attenuation parameters of HDPE filled with different nano-size and Bulk WO3

High-density polyethylene (HDPE) was obtained through a compression molding technique, and incorporated with different filler weight fractions (0, 10, 15, 25, and 35%) of bulk WO3, and two different WO3 nanoparticle sizes (45 nm and 24 nm). The radiation attenuation ability of the new category of polymer composite HDPE/WO3 was evaluated using gamma-ray energies ranging from 59.53 up to 1332.5keV of four radioactive sources 241Am, 133Ba, 137Cs, and 60Co. The mass attenuation coefficients μm, the total molecular cross-section σmol, the effective atomic cross-section σatom, the total electronic cross-section σel, the effective atomic number Zeff, electron density Neff, the half value layer (HVL), the tenth value layer (TVL), and the relaxation length were investigated. The obtained results of the gamma-ray attenuation parameters exhibited an outstanding influence of the size and weight fraction of WO3 filler on the gamma-ray shielding ability of the HDPE composite. A significant improvement was detected at low gamma-ray energies. The HVL of the synthesized HDPE composites is compared with that of pure lead as a conventional shielding material. HDPE composite filled with the smaller size of WO3 nanoparticle shows good improvement in the attenuation parameters, which suggests promising applications in radiation protection and gamma-ray shielding.

Combined electronic excitation and knock-on damage in monolayer MoS2

Electron irradiation-induced damage is often the limiting factor in imaging materials prone to ionization or electronic excitations due to inelastic electron scattering. Quantifying the related processes at the atomic scale has only become possible with the advent of aberration-corrected (scanning) transmission electron microscopes and two-dimensional materials that allow imaging each lattice atom. While it has been shown for graphene that pure knock-on damage arising from elastic scattering is sufficient to describe the observed damage, the situation is more complicated with two-dimensional semiconducting materials such as ${\mathrm{MoS}}_{2}$. Here, we measure the displacement cross section for sulfur atoms in ${\mathrm{MoS}}_{2}$ with primary beam energies between 55 and 90 keV, and correlate the results with existing measurements and theoretical models. Our experimental data suggests that the displacement process can occur from the ground state, or with single or multiple excitations, all caused by the same impinging electron. The results bring light to reports in the recent literature, and add necessary experimental data for a comprehensive description of electron irradiation damage in a two-dimensional semiconducting material. Specifically, the results agree with a combined inelastic and elastic damage mechanism at intermediate energies, in addition to a pure elastic mechanism that dominates above 80 keV. When the inelastic contribution is assumed to arise through impact ionization, the associated excitation lifetime is on the order of picoseconds, on par with expected excitation lifetimes in ${\mathrm{MoS}}_{2}$, whereas it drops to some tens of femtoseconds when direct valence excitation is considered.

Application of spectrum smoothing to improve the accuracy of atomic inner-shell ionization cross sections impacted by electron near the threshold energy

In this study, the X-ray spectrum smoothing is applied to improve the reading precision of the experimental X-ray peak net counts. The experimental Sn L-shell X-ray production cross sections (XRPCSs) and Bi-Mαβ XRPCSs before and after smoothing are compared, respectively. The result shows that spectrum smoothing effectively improves the accuracy of the experimental XRPCSs. The after-smoothing present XRPCSs agree well with the distorted wave Born approximation (DWBA) theoretical XRPCSs and are consistent with the previously published XRPCSs within the experimental uncertainty. Finally, the factors affecting the comparison between the experimental and DWBA theoretical XRPCSs are analyzed.

Assessment of X-ray shielding properties of polystyrene incorporated with different nano-sizes of PbO.

PbO (lead oxide) particles with different sizes were incorporated into polystyrene (PS) with various weight fractions (0, 10, 15, 25, 35%). These novel PS/PbO nano-composites were produced by roll mill mixing and compressing molding techniques and then investigated for radiation attenuation of X-rays (N-series/ISO 4037) typically used in radiology. Properties of the PbO particles were studied by X-ray diffraction (XRD). Filler dispersion and elemental composition of the prepared nano-composites were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), revealing better filler distribution and fewer agglomerations with smaller PbO particle size. Linear and mass attenuation coefficients (μ and μm), total molecular and atomic cross-sections (σmol and σatm), as well as effective atomic number and electron density (Zeff and Neff), were calculated for the energy range N40 to N200. The influence of PbO weight percentage on the enhancement of the shielding parameters of the nano-composites was expected; however, the effect of PbO particle size was surprising. Linear and mass attenuation coefficients for PS/PbO composites increased gradually with increasing PbO concentrations, and composites with a small size of nanoparticles showed best performance. In addition, increasing PbO concentration raised the effective atomic number Zeff of the composite. Hence, the electron density Neff increased, which provided a higher total interaction cross-section of X-rays with the composites. Maximum radiation shielding was observed for PS/PbO(B). It is concluded that this material might be used in developping low-cost and lightweight X-ray shielding to be used in radiology.

Research on atomic structure and collision cross-sections for spectroscopic modeling in KAERI Atomic Data Center

Research on atomic structure and collision cross-sections for spectroscopic modeling in KAERI Atomic Data Center

X-ray scattering and attenuation cross-sections and coefficients of bone, brain, lung, fat, and soft tissue for applications in dosimetry, cancer detection, and treatment

The Klein-Nishina electronic and atomic cross-sections and Compton mass attenuation coefficients of the bone, lung, soft tissue, brain, and fat are calculated for X-ray or γ-ray energies of 50 keV, 140 keV, 364 keV, 1.25 MeV, 4.784 MeV, and 6.0 MeV. The Klein-Nishina formula was used in the entire calculation. The results show that the Klein-Nishina electronic cross-section (eσ) decreases with increasing photon energy. Due to the complex variation in the effective charge number Z of the tissues, the Klein-Nishina atomic cross-section (aσ) first increases and then decreases for the investigated tissues. The Compton mass attenuation coefficient (σ/ρ) has even more complexity when the calculated values of σ/ρ are analyzed as a function of increasing Z/A for the investigated tissues. An overall trend of increase in σ/ρ is observed for increasing Z/A for all tissues except the cortical bone. In the case of the cortical bone, the values of σ/ρ decrease since cortical bone is a relatively high Z tissue as compared to other tissues where a rapid increase in the effective mass number A occurs when Z is increased. Overall, the results are very useful in calculating and delivering precise and optimum doses to avoid image quality degradation in radiographic images and to treat a tumor more effectively while keeping the normal tissues safe in radiation treatment planning.

Evidence of production of keV Sn+ ions in the H2 buffer gas surrounding an Sn-plasma EUV source

Charge-state-resolved kinetic energy spectra of Sn ions ejected from a laser-produced plasma (LPP) of Sn have been measured at different densities of the H2 buffer gas surrounding a micro-droplet LPP. In the absence of H2, energetic keV Sn ions with charge states ranging from 4+ to 8+ are measured. For the H2 densities used in the experiments no appreciable stopping or energy loss of the ions is observed. However, electron capture by Sn ions from H2 results in a rapid shift toward lower charge states. At the highest H2 pressure of mbar, only Sn2+ and Sn+ ions are measured. The occurrence of Sn+ ions is remarkable due to the endothermic nature of electron capture by Sn2+ ions from H2. To explain the production of keV Sn+ ions, it is proposed that their generation is due to electron capture by metastable Sn ions. The gateway role of metastable Sn is underpinned by model simulations using atomic collision cross sections to track the charge states of Sn ions while traversing the H2 buffer gas.

Photon attenuations of trichloride of gadolinium by Geant4 and XCom: a comparative study

The total mass attenuation coefficient of trichloride gadolinium has been investigated utilizing Geant4 compared with WinXCom simulation data at energies; 1–10 MeV. The simulated results are used to calculate the total cross section, atomic and electronic cross sections. The aim of this work is to characterize new materials and their interactions with radiation in order to be able for using in shielding or detection. The GdCl3 is applied for super–Kamiokande detector of neutrons. From our comparison study, it is found that the mass attenuation coefficient of GdCl3 with those of two detectors of X-ray (Si and CdTe) is very closed. Also, the total mass transfer attenuation coefficient increases as high energies increases at pairs effect production. From our comparison study, we can predict that GdCl3 can be a good detector of X-ray and concluded that this material has shown good interaction with electromagnetic radiations at high energies.

Mechanical anisotropy of hair affected by genetic diseases highlights structural information related to differential crosslinking in keratins.

Previous work with Atomic Force Microscope (AFM) nanoindentation, on longitudinal and cross-sections of the human hair fibre, allowed for the derivation of a model for the mechanical behaviour of human hair, called the Anisotropic Index. Expanding that research further, and by applying this model, the nanomechanical behaviour of hairs from patients with the disease Trichothiodystrophy (TTD) has been examined and structural insights, gained from combining the AFM results with Differential Scanning Calorimetry (DSC) experiments and tensile measurements, suggests that TTD-affected hairs have a relatively increased amount of Keratin Intermediate Filaments, contained in compartments of differing crosslinking extent. The associated calculations of axial and transverse Young's Moduli deliver values in good agreement with the measured fibre mechanics. Furthermore, comparing these findings with the results previously obtained from the study of hairs from patients with the disease Monilethrix, it is shown that the Anisotropic Index correlates well with the known deficiencies in both hair types obtained from such patients and allows for discerning between the Control hair and from those affected by the two diseases. AFM nanoindentation along and across the fibre axis and the Anisotropic Index thus appear to reveal structural details of hair not otherwise acquirable, whilst DSC may offer a quick and simple method for distinguishing between different severities of TTD.