Total Elastic Cross Sections Research Articles

First Study of Antihyperon-Nucleon Scattering Λ[over ¯]p→Λ[over ¯]p and Measurement of Λp→Λp Cross Section.

Using (10.087±0.044)×10^{9} J/ψ events collected with the BESIII detector at the BEPCII storage ring, the processes Λp→Λp and Λ[over ¯]p→Λ[over ¯]p are studied, where the Λ/Λ[over ¯] baryons are produced in the process J/ψ→ΛΛ[over ¯] and the protons are the hydrogen nuclei in the cooling oil of the beam pipe. Clear signals are observed for the two reactions. The cross sections in -0.9≤cosθ_{Λ/Λ[over ¯]}≤0.9 are measured to be σ(Λp→Λp)=(12.2±1.6_{stat}±1.1_{syst}) and σ(Λ[over ¯]p→Λ[over ¯]p)=(17.5±2.1_{stat}±1.6_{syst}) mb at the Λ/Λ[over ¯] momentum of 1.074 GeV/c within a range of ±0.017 GeV/c, where the θ_{Λ/Λ[over ¯]} are the scattering angles of the Λ/Λ[over ¯] in the Λp/Λ[over ¯]p rest frames. Furthermore, the differential cross sections of the two reactions are also measured, where there is a slight tendency of forward scattering for Λp→Λp, and a strong forward peak for Λ[over ¯]p→Λ[over ¯]p. We present an approach to extract the total elastic cross sections by extrapolation. The study of Λ[over ¯]p→Λ[over ¯]p represents the first study of antihyperon-nucleon scattering, and these new measurements will serve as important inputs for the theoretical understanding of the (anti)hyperon-nucleon interaction.

Electron Collisions with Multielectron Atoms and Fullerene Molecules: Strong Polarisation Effects

Regge pole-calculated low-energy electron elastic total cross sections for multielectron atoms/fullerenes are characterised by ground, metastable and excited negative-ion formation, shape resonances and Ramsauer-Townsend minima. In this article, we demonstrate through the total cross sections for Eu, Au and At atoms and C60 fullerene the sensitivity of stable negative-ion formation to the crucial core-polarisation potential. The energy positions of the dramatically sharp resonances corresponding to the binding energies of the formed anions during the collisions agree excellently with the measured electron affinities of the atoms and C60. The sensitivity of Ramsauer-Townsend minima and shape resonances to the electronic structure and dynamics of Bk and Cf permits their first ever use as novel validation of the experimental observation that Cf is indeed a transitional element in the actinide series. Their electron affinities are also calculated.

Study of Electron Collisions with Isoprene, 1,2-Butadiene, and Their Isomers.

Isoprene, 1,2-butadiene, and their isomers play an important role in aerosols in the atmosphere, interstellar media, and extraterrestrial life. Since electrons are everywhere, studying how electrons interact with these molecules is an important part of studying such environments. To date, however, little investigation has been conducted in this area. Bearing this in mind, we conducted a thorough investigation to report the various electron scattering cross sections of isoprene, 1,2-butadiene, and their isomers. The methods used for this purpose are reliable within the limits of adopted model potentials. The optical potential method was used to get the total elastic and inelastic cross sections, while the complex scattering potential ionization contribution method was used to get the total ionization cross section from the inelastic contribution. The results from these approximations are pretty close to the results from earlier experiments and theories. Furthermore, most of these isomers are being explored for the first time. Besides, their isomeric effect is also discussed. A correlation between the cross sections of molecules is demonstrated, which can be used to predict cross sections of those molecules where previous data are not available.

Benchmarking of the NCrystal SANS Plugin for Nanodiamonds

Nanodiamonds have attracted attention in recent years for their exceptional albedo of slow neutrons. Several theoretical models have been proposed to compute the total elastic cross section. However, these models neglect the relatively complex internal structure and chemical composition of the diamond nanoparticles, relying often on the monodisperse structureless spheres approximation. In this work, we explore the possibility of adding the small-angle neutron scattering (SANS) process for nanodiamonds to NCrystal, a library that enables calculations for Monte Carlo simulations of neutrons in polycrystalline materials and powders. This approach aims to describe the scattering process also at neutron wavelengths below the diamond Bragg cutoff where simple models usually struggle. The extension relies on modeling the SANS process through the fitting of experimental data as well as theoretical inputs. The code can then be coupled with an existing simulation framework, such as McStas, and benchmarked in different setups. We tested the plugin for two properties of diamond powder nanoparticles: the backward reflection of very cold neutrons and the quasispecular reflections of cold neutrons. The validation of this simulation tool is intended to pave the way for the design of the beam extraction system for a future high-intensity cold neutron moderator at the European Spallation Source.

Convergent close-coupling calculations of positron scattering from atomic carbon

We report on the extension of the single-center convergent close-coupling method to positron scattering on multielectron atoms, along with the development of a technique for separating the direct ionization and positronium-formation channels in single-center calculations. We have performed calculations of positron scattering on carbon and present total elastic, momentum transfer, excitation, direct ionization, total ionization, total inelastic, positronium-formation, stopping power, and total cross sections from threshold to 5000 eV. We also present oscillator strengths, the scattering length, the hidden Ramsauer-Townsend minimum, the energy of the positron-carbon virtual state, and the mean excitation energy. Agreement with electron-scattering experiment and positron-scattering theory for several cross sections has been demonstrated for high energies. However, discrepancies exist between different theoretical methods at lower energies and for the ionization and positronium-formation processes.

Rigorous Negative Ion Binding Energies in Low-Energy Electron Elastic Collisions with Heavy Multi-Electron Atoms and Fullerene Molecules: Validation of Electron Affinities

Dramatically sharp resonances manifesting stable negative ion formation characterize Regge pole-calculated low-energy electron elastic total cross sections (TCSs) of heavy multi-electron systems. The novelty of the Regge pole analysis is in the extraction of rigorous and unambiguous negative ion binding energies (BEs), corresponding to the measured electron affinities (EAs) of the investigated multi-electron systems. The measured EAs have engendered the crucial question: is the EA of multi-electron atoms and fullerene molecules identified with the BE of the attached electron in the ground, metastable or excited state of the formed negative ion during a collision? Inconsistencies in the meaning of the measured EAs are elucidated and new EA values for Bk, Cf, Fm, and Lr are presented.

Electron interactions with analogous of DNA/RNA nucleobases: 3-hydroxytetrahydroFuran and α-Tetrahydrofurfuryl alcohol

We report quantitative results for electron induced molecular processes for DNA/RNA nucleobase analogous bio-molecules, 3-hydroxytetrahydrofuran (C4H8O2, 3hTHF) and α-tetrahydrofurfuryl alcohol (C5H10O2, THFA), which are similar in structure and functional group to backbone of DNA and RNA. We have employed spherical complex optical potential (SCOP) formalism to compute total elastic (Qel) and inelastic (Qinel) cross sections and used Complex Scattering Potential-ionization contribution (CSP-ic) method to obtain total ionization (Qion) and summed total excitation (∑Qexc) cross sections. These results obtained for a wide energy range (10 eV - 5 keV) may serve as the input parameters in predicting damage in biomolecular systems induced by secondary electrons caused by primary ionization radiation. We have observed a correlation between maximum Qion and molecular polarizability volume (α), ionisation energy (IE) and number of valence electrons (Nv). This work includes an attempt to estimate ∑Qexc for these molecules in normal state.

Elastic and inelastic low-energy electron scattering from pyridine.

A comprehensive investigation of elastic and inelastic electron scattering from molecular pyridine is reported using the ab initio R-matrix method with the static exchange plus polarization and close-coupling approximations for incident energies up to 10eV. The two well-known low-lying 1 2B1 and 1 2A2 shape resonances as well as a 2 2B1 mixed-character resonance compare well with the theoretical and experimental results. We also detect five core-excited resonances (1 2A1, 1 2B2, 3 2B1, 2 2A2, and 4 2B1), which lie above the first electronic excitation threshold. The total elastic cross sections and momentum transfer cross sections agree reasonably with previous reference data. Comparisons of the differential elastic cross sections of pyridine with those measured for benzene, pyrazine, and pyrimidine show remarkable agreement at scattering angles above 40° but behave differently for forward scattering below 40° below 6eV, due to the dominant effect of the permanent dipole moment on the differential cross section in the low energy region with narrow scattering angles. Inelastic electronic excitation cross sections are presented, showing the influence of core-excited resonances below the ionization threshold for the first time.

Low-Energy Electron Elastic Total Cross Sections for the Large Actinide Atoms Cf, Fm and Md

The rigorous Regge pole method has been used to investigate negative-ion formation in the large actinide atoms Cf, Fm and Md through the elastic total cross sections (TCSs) calculation in the electron impact energy range 0.0 ≤ E ≤ 10.0eV. Ground, metastable and excited negative-ion formation as well as shape resonances (SRs) and Ramsauer-Townsend (R-T) minima are found to characterize generally the TCSs which also exhibit fullerene molecular behavior near threshold through the TCSs of the highest excited states, while maintaining atomic character through the ground state TCSs. Additionally, a polarization-induced metastable TCS with a pronounced SR appears for the first time very close to threshold in the Cf TCSs, having flipped over from a deep R-T minimum near threshold in the Bk TCSs. This behavior manifests the impact of the size effect and the 6d-orbital collapse as well as demonstrates the sensitivity of the R-T minima and the SRs to the electronic structure of these atoms, thereby permitting their first ever use as novel confirmation of Cf as a transitional element in the actinide series. Rigorous and unambiguous ground, metastable and excited anionic states BEs extracted from the TCSs are compared with the existing electron affinities.

Structural, spectroscopic and electron collisional studies of isoxazole (C3H3NO)

• Comprehensive structural, spectroscopic and electron collision data of Isoxazole. • DFT calculations of ground state geometry and vibrational frequencies. • Comparison with earlier data; confirmation/revision of vibronic assignments. • Vertical excitation energies for singlet and triplet states using TDDFT. • Low energy electron scattering data for Isoxazole from 0.1-20 eV. The structural, spectroscopic, and electron collision data of Isoxazole (C 3 H 3 NO) were subjected to extensive computational studies. Spectroscopic calculations were performed on ground and excited states using the density functional theory (DFT) and the time dependent density functional theory (TDDFT) respectively. Ground state geometry and vibrational frequencies agree well with earlier works and lead to re-assignment of a few vibrational bands. Theoretically predicted singlet and triplet excitation energies are in good agreement with earlier experimental data, while predicted oscillator strengths of singlet states correlate well with the observed relative spectral intensities. The electron collision data for isoxazole molecule were calculated using Quantemol-N, which employs the UK Molecular R-matrix codes. These calculations were performed for the total elastic cross-sections along with their symmetrical components, differential and momentum transfer cross-sections, inelastic scattering cross-sections comprising of discrete electronic excitation, ionization and dissociative electron attachment processes. We employed the two most popular theoretical approaches to calculate the electron impact ionization cross-sections viz. Complex scattering potential-ionization contribution (CSP-ic) and the Binary encounter Bethe (BEB) model. The rate coefficients for elastic and inelastic processes were estimated over a wide electron temperature range. In addition to scattering calculations, the other motivation was to obtain resonances which are signatures of many significant low energy phenomena. The first two peak correspond to π* shape resonances which are observed at 2.1 eV and 4.69 eV and are in accordance with the earlier reported data. The third peak is observed at 10.96 eV which may be attributed to the σ* shape resonance.

Low-Energy Electron Elastic Collisions with Actinide Atoms Am, Cm, Bk, Es, No and Lr: Negative-Ion Formation

The rigorous Regge-pole method is used to investigate negative-ion formation in actinide atoms through electron elastic total cross sections (TCSs) calculation. The TCSs are found to be characterized generally by negative-ion formations, shape resonances and Ramsauer-Townsend(R-T) minima, and they exhibit both atomic and fullerene molecular behavior near the threshold. Additionally, a polarization-induced metastable cross section with a deep R-T minimum is identified near the threshold in the Am, Cm and Bk TCSs, which flips over to a shape resonance appearing very close to the threshold in the TCSs for Es, No and Lr. We attribute these new manifestations to size effects and orbital collapse significantly impacting the polarization interaction. From the TCSs unambiguous and reliable ground, metastable and excited states negative-ion binding energies (BEs) for Am−, Cm−, Bk−, Es−, No− and Lr− anions formed during the collisions are extracted and compared with existing electron affinities (EAs) of the atoms. The novelty of the Regge-pole approach is in the extraction of the negative-ion BEs from the TCSs. We conclude that the existing theoretical EAs of the actinide atoms and the recently measured EA of Th correspond to excited anionic BEs.

A novel method to obtain integral parameters of the orientation distribution function of textured polycrystals from wavelength-resolved neutron transmission spectra

A novel method to estimate integral parameters of the orientation distribution function (ODF) in textured polycrystals from the wavelength-resolved neutron transmission is presented. It is based on the expression of the total coherent elastic cross section as a function of the Fourier coefficients of the ODF. This method is broken down in detail for obtaining Kearns factors in hexagonal crystals, and other material properties that depend on the average of second- and fourth-rank tensors. The robustness of the method against three situations was analyzed: effects of sample misalignment, of cutoff value l max of the series expansion and of experimental standard deviation. While sample misalignment is shown not to be critical for the determination of Kearns factors and second-order-rank properties, it can be critical for fourth-rank and higher-order tensor properties. The effect of the cutoff value on the method robustness is correlated to the standard deviation of the experimental data. In order to achieve a good estimation of the Fourier coefficients, it is recommended that the experimental standard deviation be around 3–5% of the total scattering cross section of the material for the method to be stable. The method was applied for the determination of Kearns factors from transmission measurements performed at the instrument ENGIN-X (ISIS) on a Zr–2.5 Nb pressure tube along two sample directions and was shown to be able to estimate Kearns factors with an error below 5%.

Feshbach resonances of nonzero partial waves at different collision energies

Taking the ultracold 85Rb–87Rb collision system as an example, we investigated the Feshbach resonances of nonzero partial waves above the threshold. The self-energy at the threshold, which represents the coupling strength between open and closed channels, is considered a critical parameter to quantitatively describe the properties of Feshbach resonances. The total elastic and inelastic cross sections are calculated as functions of the magnetic field B and collision energy E col, ranging from 0.1 to 600 μK. For a large absolute value of the self-energy at the threshold, the resonance decays rapidly with increasing collision energy, and narrow resonances of nonzero partial waves can be clearly resolved in the contour plot of the inelastic cross section versus the collision energy and magnetic field. It was found that the resonance tail appeared at the given magnetic field when the cross section decreased from the maximal value of the resonance peak to the minimum value, where a long resonance tail indicates an appreciable resonance in a relatively large region of collision energy. This relationship between the self-energy and the properties of Feshbach resonances still exists in the thermally averaged inelastic rate coefficient. The bound-state energies for nonzero partial waves split owing to the spin–spin interaction, which results in multiple nearly-overlapping resonances. Both the spin–spin and second-order spin–orbit effects are included. However, multiple nearly-overlapping resonances for nonzero partial waves are difficult to resolve in thermally averaged rate coefficients.

Determination of the asymmetry term strength in the n–A elastic scattering process using a nonlocal optical model

In previous works, the imaginary surface and (or) the imaginary volume depths of the optical potential were parametrized as linear functions of the projectile’s incident energy and neutron-proton asymmetry (N – Z)/A of the target nucleus. However, the obtained asymmetry strength parameters were not robust nor unique. In this work, we determine values for the strength parameters by simultaneously fitting 38 angular distribution data sets corresponding to neutron elastic scattering off chains of isotopes. For each isotopic chain, we considered the data sets that are measured at the same energy. This minimises the effect of the known energy dependence of the optical model and projects the dependence on the asymmetry term, which in turn leads to more reliable values of the strength parameters. To demonstrate the significance of the obtained strength values, we use the model to predict elastic angular distributions for neutron scattering off nuclei not considered in the χ2 analysis. Our theoretical angular distributions are in good agreement with the measured data and are also comparable to the predictions of local global models. In addition, our predicted total elastic and total reaction cross sections are in fair overall agreement with experiment. An additional result of this work is the determination of a global set of nonlocal parameters that describe neutron elastic scattering off nuclei that fall in the mass range 24 ≤ A ≤ 208 corresponding to incident neutron energies between ≈10–30 MeV.

Low-Energy Electron Elastic Total Cross Sections for Ho, Er, Tm, Yb, Lu, and Hf Atoms

The robust Regge-pole methodology wherein is fully embedded the essential electron-electron correlation effects and the vital core polarization interaction has been used to explore negative ion formation in the large lanthanide Ho, Er, Tm, Yb, Lu, and Hf atoms through the electron elastic total cross sections (TCSs) calculations. These TCSs are characterized generally by dramatically sharp resonances manifesting ground, metastable, and excited negative ion formation during the collisions, Ramsauer-Townsend minima, and shape resonances. The novelty and generality of the Regge-pole approach is in the extraction of the negative ion binding energies (BEs) of complex heavy systems from the calculated electron TCSs. The extracted anionic BEs from the ground state TCSs for Ho, Er, Tm, Yb, Lu, and Hf atoms are 3.51 eV, 3.53 eV, 3.36 eV, 3.49 eV, 4.09 eV and 1.68 eV, respectively. The TCSs are presented and the extracted from the ground; metastable and excited anionic states BEs are compared with the available measured and/or calculated electron affinities. We conclude with a remark on the existing inconsistencies in the meaning of the electron affinity among the various measurements and/or calculations in the investigated atoms and make a recommendation to resolve the ambiguity.

Electron elastic collisions with Pu, Am and Lr actinide atoms

SynopsisThe robust Regge-pole methodology which embeds the crucial electron correlations and the vital core-polarization interaction is used to explore negative-ion formation in the actinide atoms Pu, Am and Lr through the electron elastic total cross sections (TCSs) calculation. The TCSs are found to be characterized by ground, metastable and excited anionic formation, whence we extract the anionic binding energies and compare them with existing electron affinities. The TCSs exhibit both atomic and molecular behavior in addition to polarization-induced metastable TCSs.

Negative ion formation in fullerene molecules C44, C74, C100, C124 and C136: determination of their electron affinities

SynopsisHere we investigate through the electron elastic total cross sections (TCSs) calculations the variation of the electron affinity (EA) with the fullerene size from C44 to C136 and contrast their EAs with that of C60. The TCSs are found to be characterized generally by ground, metastable and excited anionic formation during the collisions. The extracted ground state anionic binding energies for C44, C74, C100, C124 and C136 are 3.25eV, 4.03eV, 3.67eV, 3.06 eV and 3.75eV, respectively. These corresponding to the fullerenes EAs demonstrate their wide variation.

Electron elastic scattering from Ho, Er, Tm, Yb, Lu and Hf atoms

SynopsisWe carefully investigate negative ion formation in the large lanthanide atoms Ho, Er, Tm, Yb and Lu as well as in atomic Hf through the electron elastic total cross sections (TCSs) calculation using the robust Regge-pole methodology. The TCSs are found to be characterized generally by ground, metastable and excited states negative ion formation. The extracted from the TCSs anionic binding energies (BEs), with those for the ground states corresponding to the definitive and unambiguous electron affinities (EAs), are contrasted with the measured and/or calculated EAs.

Identification of characteristic features in scattering cross sections for the electrons colliding with silver, platinum, and gold atoms

A semi-relativistic approach is employed to calculate elastic differential, integral, and momentum transfer cross sections as well as total (elastic plus inelastic) cross sections for the scattering of electrons from silver, platinum, and gold atoms in the energy range 0.1–100 eV. The projectile-target interaction is composed of real (i.e. the sum of static, exchange, and polarization) and imaginary (i.e. absorption) potential. The total optical potential is then used in the solution of the Dirac equation for the scattered electrons. The characteristic features [Ramsauer-Townsend (RT) minimum and shape resonance] which are required for the fundamental understanding of the dynamic processes at the atomic level, are identified in the low energy region. The value of the RT minimum has been correlated with the scattering length to the dipole polarizability of the target atom. The calculated cross sections are compared with available theoretical calculations and experimental measurements in this energy region.

Angle-Resolved Electron Scattering from H2O near 0°

An electron beam, characterized by a high-angular discrimination (≃0.7°), has been used to measure the total (elastic plus inelastic) cross section of H_{2}O in the energy range 3-100eV. Broad coincidence is found with recent experiments, including a pronounced shoulder in the 6-12eV region. However, at energies ≲6 eV, the present cross sections are ≃30% higher. Furthermore, forward scattering has been probed in the angular range 0°-3.5° and measures of the average (rotationally and vibrationally summed) differential elastic cross sections for incident energies ≤12 eV are obtained at a scattering angle ≃1^{∘}. The measurements, which provide the first test of theoretical predictions in an angular region experimentally unexplored until now, are found to be within 1 standard deviation of corresponding abinitio R-matrix calculations.