Absolute Values Of Cross Sections Research Articles

Differences and similarities in optical properties of coated fractal soot and its surrogates

Atmospheric soot (or black carbon, BC) affects climate through solar light absorption and scattering, which depend strongly on the particle morphology and composition. Initially, soot particles are fractal aggregates of spherules made of elemental carbon (EC), but condensation of atmospheric trace vapors adds non-EC materials and often results in particle compaction. The optical properties of such processed soot differ from those of fractal soot, and the changes are caused both by particle volume increase from coating addition and by restructuring of the EC backbone. In laboratory studies of soot optics, surrogates such as carbon black (CB) and nigrosin are often used in place of flame-generated soot. Our goal was to investigate if compositional and morphological differences between these surrogates and soot may produce different processing rates and optical responses. In our experiments, we generated fractal soot, compact CB, agglomerated CB (via coagulation of compact CB), and spherical nigrosin aerosol particles, subjected them to supersaturated vapor of dioctyl sebacate (DOS) to form a coating layer, and investigated the morphological response of these four particle types to coating addition and removal. Using coated and coated-denuded aerosol particles with known composition and morphology, we quantified the contributions of volume increase and restructuring to light scattering and absorption enhancements. By comparing experimental measurements against different particle optics models we show that it is crucial to account for larger, multiply charged particles present in the mobility-classified aerosol. Producing a disproportionately high contribution to absolute values of optical cross sections, such larger particles also result in lesser optical enhancements due to slower growth by vapor condensation. Scattering increases for all particle types due to the addition of a coating layer, and also due to restructuring for fractal soot (strongly) and agglomerated CB (weakly). Absorption increases only due to coating addition caused by the coating layer for all particle types. We find that simple optical models, such as Mie, are often sufficient to provide reasonable closure with experimental results for bare and coated aerosols, but only after accounting for the contributions from multiply charged particles, both in terms of their stronger optical cross sections and slower condensational growth. We conclude that CB is an appropriate surrogate for soot in aerosol aging studies where the effects of restructuring do not need to be considered and that nigrosin can be used as a general model for light-absorbing aerosols but is not representative of optical properties of soot.

Similarity and distinctions of <sup>58, 60</sup>Ni photodisintegration processes

Reliability of (γ, 1n) and (γ, 2n) reactions cross sections for 58, 60Ni obtained in experiments carried out on the beams of bremsstrahlung and quasimonoenergetic annihilation photons was investigated using objective physical criteria. It was found that data of the first type experiment do not satisfy those criteria and definitely are not reliable. At the same time there are serious doubts in reliability of the data obtained in the second type experiment. New partial photoneutron reaction cross sections on 58, 60Ni satisfying physical criteria of data reliability were used for analysis of characteristics of both isotope photodisintegration processes. It was obtained that for neighboring (differ in two neutrons) isotopes because of various type systematic uncertainties there are significant disagreements between evaluated and experimental cross sections of various reactions which for isotopes 58Ni and 60Ni are of significant different character. It was shown that the reasons are not only the differences in energy thresholds and absolute values of cross sections of the (γ, 1n), (γ, 1n1p) and (γ, 2n) reactions on 58Ni and 60Ni but significant differences in specific features of neighboring isotopes shell structure also.

Testing the ϕ-nuclear potential in pion-induced ϕ meson production on nuclei near threshold

The near-threshold pion-induced ϕ production off nuclei has been studied in the kinematical conditions of the HADES experiment using a collision model based on the nuclear spectral function. Starting from the elementary reaction π−p→ϕn, absolute differential and integral cross sections for the production of ϕ mesons off a light carbon and a heavy tungsten target have been calculated and compared to the recently reported experimental cross sections. The absolute cross section values are shown to be sensitive to the effective nuclear scalar ϕ and neutron potentials while the transparency ratio is governed by the ϕN absorption cross section. The experimental data are found to be consistent with an attractive ϕ-nucleus potential of ≈ -(50–100) MeV at normal nuclear matter density ρ0 and an effective ϕN absorption cross section of ≈ 12–25 mb. The extracted ϕ-nucleus potential is deeper than previous theoretical and experimental findings as well as those obtained in the present work within the (tρ) approximation with accounting for Pauli correlations from the spin-averaged ϕ-p scattering length reported in a recent ALICE experiment.

Spectral electron energy map of electron impact induced emission of nitrogen

The processes of electron impact induced fluorescence of nitrogen were studied in the electron energy range from 6 to 100 eV and in the spectral range from 330 to 1030 nm. Using the new CCD camera a Spectral Electron Energy Map of N2 was obtained. This type of data for such a wide spectral and energy range are published for the first time. The most intensive molecular emission bands were neutral nitrogen First positive system N2 (B3Πg − A3∑u+) and Second positive system N2 (C3Πu − B3Πg), First negative system N2+ (B2∑u+ − X2∑g+) and Meinel system N2+ (A2Πu − X2∑g+). The detected lower intensity transitions were Gaydon-Herman singlet system N2 (1Σu+ − a1Πg / 1Πu+ − a1Πg) and Gaydon-Green system N2 (H3Φu − G3Δg). In addition, processes of dissociative excitation and ionisation were observed, resulting in the photon emission from the neutral and singly ionised nitrogen atoms. The provided Spectral Electron Energy Map allows extraction of (i) electron energy resolved emission spectra of N2 and determination of the absolute values of excitation-emission cross sections, (ii) excitation-emission functions for any of the molecular bands or atomic lines present in the spectra.Graphic Abstract

Electronically excited states of formic acid investigated by theoretical and experimental methods

Absolute cross-section values are reported from high-resolution vacuum ultraviolet (VUV) photoabsorption measurements of gas-phase formic acid (HCOOH) in the photon energy range 4.7–10.8 eV (265–115 nm), together with quantum chemical calculations to provide vertical energies and oscillator strengths. The combination of experimental and theoretical methods has allowed a comprehensive assignment of the electronic transitions. The VUV spectrum reveals various vibronic features not previously reported in the literature, notably associated with (3pa′←10a′), (3p′a′←10a′), (3sa′←2a″) and (3pa′←2a″) Rydberg transitions. The assignment of vibrational features in the absorption bands reveal that the C=O stretching, v3′a′, the H′–O–C′ deformation, v5′a′, the C–O stretching, v6′a′, and the O=C–O′ deformation, v7′a′ modes are mainly active. The measured absolute photoabsorption cross sections have also been used to estimate the photolysis lifetime of HCOOH in the upper stratosphere (30–50 km), showing that solar photolysis is an important sink at altitudes above 30 km but not in the troposphere. Potential energy curves for the lowest-lying electronic excited states, as a function of the C=O coordinate, are obtained employing time dependent density functional theory (TD-DFT). These calculations have shown the relevance of internal conversion from Rydberg to valence character governing the nuclear dynamics, yielding clear evidence of the rather complex multidimensional nature of the potential energy surfaces involved.

Absolute Double-Differential Cross Sections of Ultrasoft Isochromatic X-ray Radiation in Electron Scattering on Atoms

We calculate double-differential cross sections of ultrasoft X-ray bremsstrahlung in electron scattering by Ar, Kr, and Xe atoms in the soft-photon approximation. The calculations are done for the isochromatic spectra (i.e., dependence on the electron energy at a fixed photon energy of 165 and 177 eV). The results are consistent with the absolute values of the differential cross sections measured by Gnatchenko et al. (Phys. Rev. A 80, 022707 (2009)) for the above-mentioned photon energies. For low electron energies, our theoretical isochromatic spectra are in quantitative agreement with the experimental data for Ar. For Kr, the agreement is qualitative while agreement with the Xe data is poor.

Bremsstrahlung at the Nonresonant Inelastic Scattering of a Photon by an Atomic Ion

The analytical structure, absolute value, and angular anisotropy of the double differential cross section for bremsstrahlung at the nonresonant inelastic scattering of an X-ray photon by a multicharged helium-like atomic ion have been theoretically predicted.

Low-lying electronic states of ethanol investigated by theoretical and synchrotron radiation methods

We investigate the ethanol absorption spectrum in the range 5.64–10.78 eV (220–115 nm), by combining ab initio theoretical and experimental methods in order to provide the most accurate and up-to-date information about the electronic state spectroscopy of ethanol. In particular, absolute cross-section values are reported from high-resolution vacuum ultraviolet (VUV) photoabsorption measurements. The present VUV spectrum reveals several new features not previously reported in the literature, with particular reference to the Rydberg (ndσ, ndσ′ ← (3a′′/13a)), n ≥ 3 members of the Rydberg (ndπ′(a′) ← (3a′′/13a)) and n = 3 members of the Rydberg (npσ′ ← (10a′/12a)) transitions. The experimental absolute photoabsorption cross sections have subsequently been used to calculate the photolysis lifetime of ethanol in the Earth's atmosphere (0–50 km), showing that solar photolysis is expected to be a weak sink at altitudes lower than 40 km to ●OH radical reactions. Potential energy curves for the lowest-lying excited electronic states, as a function of the O–H and the C–OH coordinates, are also obtained employing the equation of motion coupled cluster single and doubles (EOM-CCSD) and time dependant density functional theory (TD-DFT) methods. These show clear dissociation character at inter-nuclear distances greater than 2.0 Å for the RO–H and 2.2 Å for the RC–OH bond lengths, indicating the rather complex multidimensional character of the potential energy surfaces involved.

Hard exclusive meson production in muon scattering at COMPASS

We report on measurements of hard exclusive muoproduction of ρ0, ω and π0 mesons on the proton at COMPASS using 160 GeV/c polarized μ+ and μ− beams scattering off a liquid hydrogen target. The extracted Spin Density Matrix Elements for vector mesons indicate a violation of s-channel helicity conservation for transitions of transversely polarized virtual photons to longitudinally polarized vector mesons, γT → VL, where V denotes ρ0 or ω meson. Additionally, for ρ0 production we observe a dominant contribution of natural-parity-exchange transitions and a small contribution of unnaturalparity-exchange transitions. On the contrary, the contribution of unnaturalparity-exchange for ω production is significant and it decreases with increasing W, being still non-negligible at the largest W values accessible at COMPASS. Further, we present also the absolute value of the differential cross section for exclusive π0 production and its dependence on squared four-momentum transfer t and azimuthal angle ø between the scattering plane and π0 production plane. The results provide an important input for modeling Generalized Parton Distribution (GPDs), and in particular to constrain chiral-odd (transversity) GPDs.

Elastic and absorption electron collisions with acetaldehyde

We report a theoretical–experimental investigation on elastic electron scattering by acetaldehyde (CH $$_3$$ CHO) in the 0.5–800 eV energy range. Theoretically, the Pade approximation and the single-center partial-wave expansion method were applied to solve the Lippmann–Schwinger scattering equation, whereas a molecular complex optical potential was used to describe the electron–molecule interaction. Calculations in the independent-atom framework were also performed. Angular distributions of the elastically scattered electrons were measured in the 10 $$^{\circ }$$ –130 $$^{\circ }$$ and 30–800 eV ranges using a crossed beams geometry. Absolute values of differential cross sections were derived by the relative flow technique. In addition, integral and momentum transfer cross sections were obtained from the experimental and theoretical differential cross sections via a numerical integration procedure. Comparison between our results and previous experimental and theoretical calculations is made.

A new approach to determine the absolute photodissociation cross section of molecules in a cell

AbstractWe demonstrate a method to determine the absolute value of the photodissociation cross section of a molecule of interest in a cell without knowing its absolute concentration. The target molecule can be either stable or unstable species. Proof‐of‐principle experiments have been demonstrated for the UV cross sections of CH2I2 and NO2. The relative concentrations of the target molecule were measured by monitoring its time‐resolved UV–visible absorption spectra with a high‐speed CMOS‐camera spectrometer before and after its photodissociation by a pulsed 248‐ or 352‐nm excimer laser beam. The absolute value of the photodissociation cross section can be deduced from the used laser fluence. The inhomogeneity of the photolysis laser beam has been found to be the major source of systematic error. However, this effect can be corrected by performing a calibration experiment on a molecule of which the photodissociation cross section is known. In some cases, post‐photolysis reactions may affect the measurements. If the kinetics of the post‐photolysis reactions is known, it is feasible to estimate their effect and retrieve the correct value of the photodissociation cross section. To our best knowledge, this is the first demonstration of such a method.

Setting Bounds on Entangled Two-Photon Absorption Cross Sections in Common Fluorophores

Excitation with entangled photon pairs may lead to an increase in the efficiency of two-photon absorption at low photon flux. The corresponding process, entangled two-photon absorption (E2PA), has been investigated in numerous theoretical and experimental studies. However, significant ambiguity and inconsistency remain in the literature about the absolute values of E2PA cross-sections. Here, we use a fluorescence-based registration scheme to experimentally determine upper bounds on the cross-sections for six fluorophores. These bounds are up to four orders of magnitude lower than the smallest published cross-section. For two samples that have been studied by others, Rhodamine 6G and 9R-S, we measure upper bounds four and five orders of magnitude lower than the previously reported cross-sections.

Elastic Electron Scattering from Methane Molecule in the Energy Range from 50-300 eV.

Electron interaction with methane molecule and accurate determination of its elastic cross-section is a demanding task for both experimental and theoretical standpoints and relevant for our better understanding of the processes in Earth’s and Solar outer planet atmospheres, the greenhouse effect or in plasma physics applications like vapor deposition, complex plasma-wall interactions and edge plasma regions of Tokamak. Methane can serve as a test molecule for advancing novel electron-molecule collision theories. We present a combined experimental and theoretical study of the elastic electron differential cross-section from methane molecule, as well as integral and momentum transfer cross-sections in the intermediate energy range (50–300 eV). The experimental setup, based on a crossed beam technique, comprising of an electron gun, a single capillary gas needle and detection system with a channeltron is used in the measurements. The absolute values for cross-sections are obtained by relative-flow method, using argon as a reference. Theoretical results are acquired using two approximations: simple sum of individual atomic cross-sections and the other with molecular effect taken into the account.

Perfluoro effect on the electronic excited states of para-benzoquinone revealed by experiment and theory

We report a comprehensive study on the electronic excited states of tetrafluoro-1,4-benzoquinone, through high-resolution vacuum ultraviolet photoabsorption spectroscopy and time-dependent density functional theory calculations performed within the nuclear ensemble approach. Absolute cross section values were experimentally determined in the 3.8-10.8 eV energy range. The present experimental results represent the highest resolution data yet reported for this molecule and reveal previously unresolved spectral structures. The interpretation of the results was made in close comparison with the available data for para-benzoquinone [Jones et al., J. Chem. Phys., 2017, 146, 184303]. While the dominant absorption features for both molecules arise from analogous π* ← π transitions, some remarkable differences have been identified. The perfluoro effect manifests in different ways: shifts in band positions and cross sections, appearance of features associated with excitations to σCF* orbitals, and spectrum broadening by quenching of either vibrational or Rydberg progressions. The level of agreement between experiment and theory is very satisfactory, yet that required the inclusion of nuclear quantum effects in the calculations. We have also discussed the role of temperature on the absorption spectrum, as well as the involvement of core-excited resonances in promoting dissociative electron attachment reactions in the 3-5 eV range.

Theoretical Calculations of Electron Excitation of the Lowest Autoionization States of the Rb Atom

Purpose. The value of the autoionization cross section and its energy dependence are determined to a great extent by excitation and subsequent electron decay of the lowest energy states. Recently, experimental data on the excitation cross sections of the rubidium atom lowest doublet (4p55s2)2P3/2,1/2 and quartet (4p54d5s)4P1/2,3/2,5/2 autoionizing states were obtained which promoted their theoretical investigations. Methods. Theoretical calculations were performed using the Flexible Atomic Code universal program package which takes account of the relativistic nature of the complex atoms excitation by the use of the Dirac-Coulomb Hamiltonian. The radial orbitals for basic relativistic wavefunctions were obtained by solving the Dirac-Fock-Slater equation. Results. Comparison of the experimental excitation cross sections for the doublet (4p55s2)2P3/2,1/2 and quartet (4p54d5s)4P1/2,3/2,5/2 autoionizing states with available theoretical data and our relativistic calculations is presented. The results of the study of the parameter R0 for the intensity ratio for the 2P3/2 and 2P1/2 states of the 4p55s2 configuration are presented. Our calculations in the distorted waves approximation is shown to well describe the experimental data in the energy region above 70 eV. At low collision energies our calculations qualitatively predict the presence of the threshold resonant excitation; however in the energy region 20-50 eV only the R-matrix method qualitatively describes the complex nature of excitation and decay of the lowest quartet autoionizing states of the rubidium atom. Conclusions. Electron excitation of the doublet (4p55s2)2P3/2,1/2 and quartet (4p54d5s)4P1/2,3/2,5/2 autoionizing states of the rubidium atom in the collision energy range from the excitation thresholds up to 700 eV was studied in the terms of the distorted waves relativistic approximation. A comprehensive analysis of the obtained results using the available experimental and theoretical data showed that the relativistic distorted waves approximation taking into account the configurational mixing is a suitable tool for describing the autoionizing states of the rubidium atom in a wide range of collision energies and allowed one to obtain the absolute values of the experimental excitation cross sections of the (4p55s2)2P3/2,1/2 and (4p54d5s)4P1/2,3/2,5/2 states.

Study of the Mechanism of the 27Al(α, p)30Si Reaction at Eα = 30.3 MeV

The results from measuring the angular dependence of the 27Al(α, p)30Si reaction differential cross sections at 30.3 MeV α-particle energy with the formation of the final nucleus in the ground (0+) and first excited (2+; 2.235 MeV) states are presented. The experimental results are compared to calculated ones obtained by assuming there is both a mechanism of triton cluster stripping in a collective model and one of compound nucleus formation. The amplitudes of spectroscopic factors for the virtual decay of 30Si → 27Al + t are obtained using a shell model with wave functions of the 1d–2s shell nuclei in the Nilsson model, allowing for nuclear deformation and the spin–orbit interaction of nucleons. Comparison of the results from calculations and experiments shows that mechanism of triton stripping used in the FRESCO code with the obtained spectroscopic amplitudes mainly describes both the shape of angular distributions and the absolute values of the differential cross sections. The contribution from the mechanism of compound nucleus formation is notable only at large angles of proton emission.

Irradiation Test of 65-nm Bulk SRAMs With DC Muon Beam at RCNP-MuSIC Facility

Negative and positive muon irradiation tests of static random access memories (SRAMs) were performed at Muon Science Innovation Channel (MuSIC) of Research Center for Nuclear Physics (RCNP), Osaka University. The muon-induced single event upset (SEU) cross sections for 65-nm bulk SRAMs were measured. The SRAM device was irradiated by the muon beams with average momenta ranging from 37.8 to 41.0 MeV/c at the beam exit. The incident muon fluence was measured using a one-by-one muon detection system with a plastic scintillator by taking advantage of the direct current (dc) muon beam and reliable absolute values of SEU cross sections were obtained. In addition to the measurement of the SEU cross sections, we measured muonic X-rays from the irradiated device to investigate the relation between the measured SEU cross section and the emission rate of muonic X-rays associated with the stopping position of the muons as a function of incident muon momentum. The result suggested that negative muons have a significant effect on SEUs by the emission of secondary light ions via negative muon capture reaction when negative muons stop near sensitive volumes (SVs) in SRAMs.

What kind of optical model potentials should be used for deuteron stripping reactions?

This paper presents the results of a study that compares CTOM, a microscopic optical model potential (OMP), which is an optical model co-created by the China Nuclear Data Center & Tuebingen University, to CH89, which is a typical phenomenological OMP. The respective OMPs were tested by applying them to the modelling of nucleon elastic scattering and (d, p) transfer reactions involving 14C, 36S, and 58Ni targets at both low and relatively high energies. The results demonstrated that although both potentials successfully accounted for the angular distributions of both the elastic scattering and transfer cross sections, the absolute values of the transfer cross sections calculated using CTOM were approximately 25% larger than those calculated using CH89. This increased transfer cross sections allowed CTOM to produce single particle strength reduction factors for the three reactions that were consistent with those extracted from (e, e′ p) reactions as well as with more recent (p, 2p) and (p, pn) reactions. Notch tests suggested that nucleon elastic scattering and transfer reactions are sensitive to different regions of the OMP; accordingly, phenomenological OMPs, which are constrained only by elastic scattering cross sections, may not be sufficient for nucleon transfer reactions. Therefore, we suggest that microscopic OMPs, which reflect more theoretical considerations, should be preferred over phenomenological ones in calculations of direct nuclear reactions.

Possibility to produce Og293,295,296 in the reactions Ca48+Cf249,250,251

The influence of polarization effects and temperature effects on the deformations of projectilelike and targetlike densities are taken into account consistently on the potential-energy surface. The evaporation residue cross sections for hot-fusion reactions are investigated within the dinuclear system model. The calculated results have reproduced well the experimental trend and absolute value of the maximum cross sections for $3n$ and $4n$ channels. The new isotopes of $^{293,295,296}\mathrm{Og}$ were found to be as large as about 0.1--0.2 pb.

Absolute cross sections of ultra-soft x-ray radiation in electron scattering upon atoms and the soft-photons approximation

We calculated the cross sections of ultra-soft x-ray bremsstrahlung in electron scattering upon Ar, Kr and Xe. The results are consistent with the absolute values of the differential cross sections measured by Gnatchenko et al. (2009) [17] for scattering electrons with an energy of 600 eV on these atoms.