Elementary Cross Sections Research Articles

Gas laser energy characteristics with different active element cross section geometry

The models for estimating the contribution of the cross section geometry to the active medium gain of the gas laser have been considered. A testing of our method for the solving of the Helmholtz equation with different boundary conditions have been fulfilled. The next step is the complication of the model taking into account the distribution of the field intensity in the resonator.

Light-by-light scattering in ultraperipheral heavy-ion collisions at low diphoton masses

We present a study of photon-photon scattering in the mass range $W_{\gamma\gamma} < 5$ GeV. We extend earlier calculations of this cross section for $W_{\gamma\gamma}>$ 5 GeV into the low mass range where photoproduction of the pseudoscalar resonances $\eta$, $\eta^{'}(958)$ contributes to two-photon final states. We present the elementary photon-photon cross section as a function of diphoton mass $M_{\gamma\gamma}$ arising from lepton and quark loop diagrams, and the visible cross section obtained with the gamma-gamma decay branching fractions of the resonances $\eta$, $\eta^{'}(958)$, $\eta_c(1S)$, $\eta_c(2S)$, $\chi_{c0}(1P)$. We derive the corresponding cross sections in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV by folding the elementary cross section with the heavy-ion photon fluxes. We consider the dominating background of the two-photon final state which arises from gamma decays of photoproduced $\pi^{0}$-pairs. Such $\pi^{0}$-pairs contribute to the background when only two of the four decay photons are within the experimental acceptance, while the other two photons escape undetected. We reduce this background by applying cuts on asymmetries of transverse momenta of the two photons and indicate how the background can be further suppressed using a multivariate sideband analysis. We present the cross section for the signal and the background at midrapidity $|\eta| <$ 0.9, and in the forward rapidity range 2.0 $< \eta <$ 4.5.

Effect of electrolyte composition on morphology and corrosion resistance of plasma electrolytic oxidation coatings on aluminized steel

Surface modification of the aluminized ultra-low carbon interstitial free steels by the process of plasma electrolytic oxidation (PEO) is reported in the current study. Coatings were formed by using a pulsating DC power source operating at a current density of 225 mA/cm2 over the period of 15 min. The effect of the electrolyte composition on the performance and properties of the coatings was studied. Three different electrolytes with varying concentrations of sodium silicate (Na2SiO3.9H2O) and potassium hydroxide (KOH) with their proportions as 2:1, 1:1 and 1:2 were used. The elemental composition, surface and cross section morphology and thickness of the coatings were analyzed by using scanning electron microscope (SEM) rigged with an energy dispersive X-ray spectroscope (EDS). The phase composition of the samples was assessed with X-ray diffraction (XRD). The surface profile and the roughness of the coatings were analyzed with an optical profilometer. The corrosion resistance of the substrate and the coated samples was determined by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) studies in a 3.5 wt% aqueous NaCl environment along with the immersion test in a 5 wt% aqueous NaCl environment. The practical adhesion strength of the PEO coating was assessed by the scratch testing. Among all the samples, the sample PEO treated with equal proportions of silicate and KOH concentration exhibited better corrosion resistance (icorr = 1.09 × 10−5 mA/cm2, inner barrier layer resistance of 1.32 × 108 Ω-cm2 and impedance (Ω-cm2) of 107 order) along with the better adhesion strength (Lc = 16.2 N). The better corrosion performance of the sample PEO treated with equal proportions of silicate and KOH concentrations can be imputed to the higher coating thickness along with the less porous surface morphology and higher inner barrier layer resistance. The higher adhesion strength of the sample, PEO treated with equi-concentrated silicate and KOH can be ascribed to the higher coating thickness along with the less porous surface morphology.

Calculation of the normal section strength of rubcon beams using deformation diagrams

Rubber concrete (rubcon) - polymer concrete, which has high strength properties, as well as the constructions made of it. Fibrorubcon – rubber concrete with the addition of disperse reinforcement. On the basis of test results for pure bending, empirical dependencies and prerequisites for adapting existing methods for calculating the strength of normal sections of rubcon and fibrorubcon beams were obtained. These studies allow developing methods for calculating the normal cross sections of bending elements made of rubber concrete using deformation diagrams and taking into account the work of stretched polymer concrete.

Stiffness test in lateral direction of temporary wooden building supports

Temporary supports consisting of a jack, a stack of wooden cubic elements and a iron plate are used during the removal of buildings deflections by uneven raising. Where the weight of a building is rested on temporary supports with a considerable length, unintentional displacements of buildings in the horizontal direction are seen. The displacements are connected with supports deformations caused by horizontal forces acting on the building part being raised. Non-vertically installed jacks, being part of the supports, are the most frequent reason for the occurrence of such forces. The jacks are not vertical due to deformations in the stack of wooden elements, upon which they are rested. In such case, the stiffness of temporary supports is essential for the safety of the deflection removal process. Laboratory tests of temporary supports were carried out and they showed that their stiffness, understood as a horizontal force divided by a displacement in the acting direction of the force, is not constant. The stiffness of supports is decreasing as the displacement amplitude grows. A considerable decrease in supports stiffness was experienced when positive longitudinal deformations occurred in the cross section of the support elements. As a result, the unconnected elements of the supports were unable to transmit positive stresses of this number. For the investigated range of loads, the deformations of the material of the supports elements were elastic. Inelastic forces were however generated along the contact points of the elements forming part of the supports, and such forces were responsible for creating a hysteresis loop and energy dissipation by the supports. The system, when a full load-unload cycle was applied, was returning to the initial position. Higher values of the energy dissipation coefficient correspond to higher values of a displacement amplitude.

Photon--Photon Scattering in the Resonance Region at Midrapidity at the LHC

A study is presented to extend the measurements of photon-photon scattering in ultra-peripheral Pb-Pb collisions at the LHC into the mass region of the pseudoscalar resonances $\eta$ and $\eta'$. The elementary photon-photon scattering cross section is presented. The cross section for photon-photon scattering in Pb-Pb is derived by convoluting the elementary photon-photon cross section with the Pb-Pb photon luminosity. The main background to two-photon final states, arising from double $\pi^{0}$ production with two of the four decay photons escaping detection, is examined, and possible kinematical conditions are discussed to optimize the signal-to-background ratio for such measurements at mid-rapidity.

Control rod treatment for FEM based radiation transport methods

This paper presents a novel control rod treatment for finite element method (FEM) based reactor physics simulations. The new method falls into the class of homogenization methods which treat material interfaces in mesh elements by defining a representative, homogenized nuclear cross section set. In contrast to existing homogenization based cusping treatments that attempt to approximate flux-volume weighting of the cross sections, we propose to exactly integrate terms appearing in the variational form of the transport or diffusion equation over mixed material elements. This goal is achieved by defining smoothly varying cross sections in elements that straddle material boundaries. It is shown that the smoothly varying cross sections can be obtained by projecting the piecewise set of cross sections onto the set of Legendre polynomials up to a finite order. Implementation of smoothly varying cross sections is supported within the Rattlesnake radiation multiphysics code at the Idaho National Laboratory. Homogenization methods traditionally suffer from cusping effects that originate from overestimation of absorption cross sections in strongly neutron-absorbing materials as found in control rods. We demonstrate that the presented method is (1) highly effective in removing cusping effects and (2) provides accurate results based on the C5G7-TD benchmark, a time-dependent version of the C5G7 benchmark.

Reciprocity analysis of electronic stopping of slow ions

Reciprocity denotes the (approximate) equality of the electronic stopping cross section of element A in element B with the one of element B in element A. Reciprocity is expected in the energy range below ∼0.1 MeV/u. For ions heavier than protons, most measurements are performed by the transmission technique. In order to minimize nuclear energy loss, only a narrow beam of penetrating ions is allowed to enter the detector. This implies that also the electronic energy loss is underestimated. We have estimated the magnitude of the necessary correction on the basis of the PASS code and its influence on the expected reciprocity and find that reciprocity is not necessarily violated, even if the reported cross sections differ significantly. However, we also find differences between reported stopping cross sections and computed reduced stopping cross sections that we cannot reconcile on the basis of the PASS code. These differences are found to reflect the well-known Z1 structure, which is not inherent in the present version of PASS.

How accurately can we predict synthesis cross sections of superheavy elements?

Synthesis of superheavy elements beyond oganesson is facing new challenges as new target–projectile combinations are necessary. Guidance from models is thus expected for future experiments. However, hindered fusion models are not well established and predictions in the fission barriers span few MeVs. Consequently, predictions are not reliable. Strategies to constrain both fusion hindrance and fission barriers are necessary to improve the predictive power of the models. But, there is no hope to get an accuracy better than one order of magnitude in fusion–evaporation reactions leading to superheavy elements synthesis.

Coherent scattering and macroscopic coherence: implications for neutrino, dark matter and axion detection

We study the question of whether coherent neutrino scattering can occur on macroscopic scales, leading to a significant increase of the detection cross section. We concentrate on radiative neutrino scattering on atomic electrons (or on free electrons in a conductor). Such processes can be coherent provided that the net electron recoil momentum, i.e. the momentum transfer from the neutrino minus the momentum of the emitted photon, is sufficiently small. The radiative processes is an attractive possibility as the energy of the emitted photons can be as large as the momentum transfer to the electron system and therefore the problem of detecting extremely low energy recoils can be avoided. The requirement of macroscopic coherence severely constrains the phase space available for the scattered particle and the emitted photon. We show that in the case of the scattering mediated by the usual weak neutral current and charged current interactions this leads to a strong suppression of the elementary cross sections and therefore the requirement of macroscopic coherence results in a reduction rather than an increase of the total detection cross section. However, for the νe scattering mediated by neutrino magnetic or electric dipole moments coherence effects can actually increase the detection rates. Effects of macroscopic coherence can also allow detection of neutrinos in 100 eV — a few keV energy range, which is currently not accessible to the experiment. A similar coherent enhancement mechanism can work for relativistic particles in the dark sector, but not for the conventionally considered non-relativistic dark matter.

Parametrization of cross sections for elementary hadronic collisions involving strange particles

The production of strange particles (kaons, hyperons) and hypernuclei in light charged particle induced reactions in the energy range of a few GeV (2-15 GeV) has become a topic of active research in several facilities (e.g., HypHI and PANDA at GSI and/or FAIR (Germany), JLab (USA), and JPARC (Japan)). This energy range represents the low-energy limit of the string models (degree of freedom: quark and gluon) or the high-energy limit of the so-called spallation models (degree of freedom: hadrons). A well known spallation model is INCL, the Li\`ege intranuclear cascade model (combined with a de-excitation model to complete the reaction). INCL, known to give good results up to 2-3 GeV, was recently upgraded by the implementation of multiple pion emission to extend the energy range of applicability up to roughly 15 GeV. The next step, to account also for strange particle production, both for refining the high energy domain and making it usable when strangeness appears, requires the following main ingredients: i) the relevant elementary cross sections (production, scattering, and absorption) and ii) the characteristics of the associated final states. Some of those ingredients are already known and, sometimes, are already used in models of the same type (e.g., Bertini, GiBUU), but this paper aims at reviewing the situation by compiling, updating, and comparing the necessary elementary information which are independent of the model used.

Theoretical research into spatial work of a steel-reinforced-concrete statically indeterminate combined structure

The constructed mathematical model and the developed algorithm for spatial calculation of combined steel-reinforced-concrete truss systems make it possible to determine parameters of the stressed-strained state in the structures' elements. It is proven that the built mathematical model satisfies three groups of conditions: equilibrium; compatibility of deformations that link deformations and displacements; physical conditions that link efforts and deformations. Owing to the devised procedure, we performed theoretical calculations to establish the actual diagrams bending moment ‒ deflection, longitudinal force ‒ deflection depending on the magnitude and place of application of external load. The derived equalities that determine coefficients for the unknowns in a system of linear algebraic equations include the topology parameters and strength characteristics of the structures' elements. That has allowed us to search, within the framework of the developed algorithm, for a minimum of the objective function of the equally-stressed state in the elements of a spatial structure.We investigated theoretically the strength and deformability of truss steel reinforced concrete structures for symmetrical and asymmetrical loads, taking into consideration the phased operation of the system. Employing an iterative search for a minimum of the objective function of the equally-stressed state at cross sections of the spatial structure's elements has helped establish a decrease in the normal stresses compared to the structures of other type. The results obtained made it possible to design actual construction structures. Therefore, there is reason to assert the practical significance of the constructed mathematical model and the developed algorithm, which were applied when designing the new, and recalculating existing, combined steel-reinforced-concrete truss systems

Calculation of L-shell ionisation and x-ray production cross sections for some trans-uranium elements induced by protons

L-shell ionisation and x-ray production cross sections of trans-uranium elements: Np, Pu and Am, induced by protons of energies 5.00–20.00 MeV, have been calculated. The cross sections for the targets were obtained using computer codes based on the ECPSSR theory. Due to the lack of experimental data of the targets considered, in view of their radioactive, toxic and unstable nature, the calculated cross sections were subsequently validated. This was achieved using the computer codes to evaluate the ionisation and x-ray production cross sections of Uranium induced by protons of energies in the 1.00–20.00 MeV range. This study also showed that the relative x-ray line intensities associated with the ionisation and x-ray productions of the targets considered are dependent on protons energies.

Buckling of Glass Reinforced Plastic Rods of Variable Rigidity

The loss of vertical structures stability is always a very dangerous phenomenon. It is almost impossible to predict it, because it develops very quickly, avalanche-like. One solution to this problem is to increase the cross section of the compressible elements. However, this solution leads to a significant increase in weight and load on the underlying structures. It is necessary to be able to accurately determine the critical force of Fcr for various forms of compressible elements and schemes of fastening. The article presents the solution of the problem of fiberglass rods stability by the energy method in the form of Tymoshenko-Ritz, which is reduced to the problem of determining eigenvalues in the algebraic theory of matrices. In the MatLab software complex, the value of the critical load Fcr is obtained by numerical method with different stiffness and pinning schemes.

Influence of anisotropic Λ/Σ creation on the Ξ− multiplicity in subthreshold proton–nucleus collisions

We present an analysis of Ξ− baryon production in subthreshold proton–nucleus (p+A) collisions in the framework of a BUU type transport model. We propose a new mechanism for Ξ production in the collision of a secondary Λ or Σ hyperon and a nucleon from the target nucleus. We find that the Ξ− multiplicity in p+A collisions is sensitive to the angular distribution of hyperon production in the primary N+N collision. Using reasonable assumptions on the unknown elementary cross sections we are able to reproduce the Ξ− multiplicity and the Ξ−/(Λ+Σ0) ratio obtained in the HADES experiment in p+Nb collisions at sNN= 3.2 GeV energy.

$\eta$ η and $\omega$ ω mesons as new degrees of freedom in the intranuclear cascade model INCL

The intranuclear cascade model INCL (Liege Intranuclear Cascade) is now able to simulate spallation reactions induced by projectiles with energies up to roughly 15 GeV. This was made possible thanks to the implementation of multipion emission in the NN, $\Delta$ N and $\pi$ N interactions. The results obtained with reactions on nuclei induced by nucleons or pions gave confidence in the model. A next step will be the addition of the strange particles, $\Lambda$ , $\Sigma$ and kaons, in order to not only refine the high-energy modeling, but also to extend the capabilities of INCL, as studying hypernucleus physics. Between those two versions of the code, the possibility to treat the $\eta$ and $\omega$ mesons in INCL has been performed and this is the topic of this paper. Production yields of these mesons increase with energy and it is interesting to test their roles at higher energies. More specifically, studies of $\eta$ rare decays benefit from accurate simulations of its production. These are the two reasons for their implementation. Ingredients of the model, like elementary reaction cross sections, are discussed and comparisons with experimental data are carried out to test the reliability of those particle productions.

A new algorithm for size optimization of the truss structures using finite element method

The paper presents a new algorithm for size optimization of the trusses using finite element method. The objective function was established based on weight minimization of trusses . The constraint conditions were formulated based on the conditions that the structure satisfies the strength, stiffness and compatibility requirements, and equilibrium equations. Determination of internal forces, displacements and establishment of the equations are based on finite element method. In order to solve optimization problems using finite element method, the authors proposed a new method for seeking optimal solutions. For truss weight optimization, the authors proposed a coefficient and called this coefficient as “the correlation coefficient of internal forces among trusses’s elements”. This coefficient shows the relationship between the internal forces of truss elements, which was used as the basis for re-selecting the dimensions of cross section of truss elements in iterative process. The paper introduces the calculation procedure and analysis algorithm for weight optimization of planar and space trusses. The examples for weight optimization of planar and space trusses were implemented in a subroutine written in Matlab software. The calculation results using the method proposed by the authors matched with the calculation results using other methods such as Hybridized Genetic Algorithm, Harmony search method, HyperWork, etc. However, using the method proposed by the authors gives less iterative circles.

Measurement of L XRF cross sections for elements with 33 ≤ Z ≤ 51 and their interpretation in terms of L (i = 1–3) subshell vacancy decay parameters

Abstract The Li (i = 1–3) subshell integral X-ray fluorescence (XRF) cross sections have been measured for 17 elements with 33 ≤ Z ≤ 51 following photoionization by the Mn K X-rays (EKαβ = 5.96 keV). The Li (i = 1–3) subshell X-rays were measured using a low-energy Ge (LEGe) detector at an emission angle, ψ = 125°, where angle-dependent emission effects, if any, are nullified as P2(cos ψ) ∼ 0. The XRF cross sections were interpreted in terms of available sets of theoretical Li (i = 1–3) subshell photoionization cross sections, radiative transition probabilities, and the atomic vacancy decay parameters, namely, fluorescence (ωi) and Coster-Kronig (fij) yields. A set of L1 subshell fluorescence (ω1) yields was deduced for the elements with 37 ≤ Z ≤ 51 from the present measured Lγ2,3,(4) [L1-N2,3(O2,3)] XRF cross sections. The ω1 values exhibit jumps at Z = 40 and 49, which are identified to be due to cut-off of the L1L2M4,5 and L1L3M4,5 Coster-Kronig (CK) transitions predicted by calculations based on relativistic Dirac-Hartree-Slater (RDHS) model. However, the measured ω1 values are found to differ considerably from those based on the RDHS model calculations for the elements below Z = 50. The pronounced discrepancies between measured and theoretical ω1 values are likely to be due to overestimation of the L1-L2,3M4,5 CK transition rates by a factor of ∼2–3. Our experiential results demand consideration of extra-atomic relaxation from the solid-state effects and exchange splitting in many-body theoretical calculations of the low-energy CK transitions.

Thermal analysis of steel-concrete composite cross sections via CS-ASA/FA

Abstract When exposed to high temperatures, such as in a fire situation, the physical and resistance characteristics of the materials employed in the structure deteriorate as the temperature increases. This fact promotes a considerable loss in the bearing capacity and stiffness of the structural system. The verification of a structure exposed to fire depends primarily and principally on the thermal analysis of the cross section of the structural element. This analysis permits determination of the temperature variation or temperature range in the element from the boundary conditions provided by the fire model adopted. As such, this study had the objective of performing a thermal analysis in a transient regime by means of a finite element method on steel-concrete composite cross sections that are employed in civil construction through use of the Computational System for Advanced Structural Analysis/Fire Analysis (CS-ASA/FA). Two cross sections are analyzed and the results obtained were satisfactory. In addition, different iterative solution processes were adopted in the analysis. Parametric studies were also performed related to the mesh variation of the finite elements and time increase. From the results, it was possible to conclude that CS-ASA/FA can supply the necessary information when a thermo-structural analysis is performed for the evaluation of strength and stiffness losses of the structural material when exposed to fire.

Investigation of the spectral properties and magnetism of BiFeO3 by dynamical mean-field theory

Using the local density approximation plus dynamical mean-field theory (LDA+DMFT), we have computed the valence-band photoelectron spectra and magnetic excitation spectra of ${\mathrm{BiFeO}}_{3}$, one of the most studied multiferroics. Within the DMFT approach, the local impurity problem is tackled by the exact diagonalization solver. The solution of the impurity problem within the LDA+DMFT method for the paramagnetic and magnetically ordered phases produces result in agreement with the experimental data on electronic and magnetic structures. For comparison, we also present results obtained by the $\mathrm{LDA}+U$ approach which is commonly used to compute the physical properties of this compound. Our LDA+DMFT derived electronic spectra match adequately with the experimental hard x-ray photoelectron spectroscopy and resonant photoelectron spectroscopy for Fe $3d$ states, whereas the $\mathrm{LDA}+U$ method fails to capture the general features of the measured spectra. This indicates the importance of accurately incorporating the dynamical aspect of electronic correlation among Fe $3d$ orbitals to reproduce the experimental excitation spectra. Specifically, the LDA+DMFT derived density of states exhibits a significant amount of Fe $3d$ states at the position of Bi lone pairs, implying that the latter are not alone in the spectral scenario. This fact might modify our interpretation about the origin of ferroelectric polarization in this material. Our study demonstrates that the combination of orbital cross sections for the constituent elements and broadening schemes for the spectral functions are crucial to explain the detailed structures of the experimental electronic spectra. Our magnetic excitation spectra computed from the LDA+DMFT result conform well with the inelastic neutron scattering data.