Low-energy Scattering Cross Sections Research Articles

Effects of Hydrogen Bonding on Nuclear Data Development of Liquid Anhydrous HF

Anhydrous Hydrogen Fluoride (HF) at high temperatures and pressures is used to process and manufacture nuclear fuel. As HF is often used directly with uranium, correct neutron thermal scattering cross sections are crucial to criticality safety applications. Classical molecular dynamics (CMD) simulation of the flexible HF system was used to create the thermal scattering law (TSL) and cross sections. The initial 2-site model is used in LAMMPS, and it can not capture the H-bond. To correctly represent the H-bond effects, a second, 3-site model was constructed in GROMACS. The 3-site model handled H-bonds by connecting a massless charge to the molecule. Key model parameters were compared to experimental data to verify the approach and models. To get the normalized VACF, the model was compared using hydrogen and fluorine bond length, density, potential energy, and diffusion coefficient. The phonon DOSs for both models were derived from the normalized VACF. DOSs were used to estimate the TSL (S(α,β)) and neutron thermal scattering cross sections for hydrogen in HF. The TSLs were evaluated using the FLASSH code with the Schofield diffusion model. It was observed that the representation of the hydrogen bonding changes the TSL's diffusional contributions. This is represented in the low energy scattering cross section, where intermolecular binding effects shift the cross section.

Very low-energy nucleon-O16coupled-channel scattering: Results with a phenomenological vibrational model

We employ a collective vibration coupled-channel model to describe the nucleon-16O cluster systems, obtaining low-excitation spectra for 17O and 17F. Bound and resonance states of the compound systems have been deduced, showing good agreement with experimental spectra. Low energy scattering cross sections of neutrons and protons from 16O also have been calculated and the results compare well with available experimental data.

Low energy scattering cross sections forn+Li6,7reactions using the continuum-discretized coupled-channels method

Low energy scattering cross sections for<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>n</mml:mi><mml:mo>+</mml:mo><mml:mmultiscripts><mml:mi>Li</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>6</mml:mn><mml:mo>,</mml:mo><mml:mn>7</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math>reactions using the continuum-discretized coupled-channels method

Experimental search for long-range forces in neutron scattering via a gravitational spectrometer

In this work we introduce a method of measuring low-energy scattering cross section with a gravitational spectrometer. In this method we add atoms (i.e., He) to the gravitational spectrometer filled with a target gas of ultracold neutrons (UCN). We search for long-range forces between atoms and UCN by measuring transfer of a small recoil energy $\ensuremath{\sim}{10}^{\ensuremath{-}7}$ eV using the gravitational spectrometer. As a result of this search we set new constraints on the strength of long-range forces within the range of the effective radius of interaction of ${10}^{\ensuremath{-}7}$--${10}^{\ensuremath{-}4}$ cm.

Spectral singularities and zero energy bound states

Single particle scattering around zero energy is re-analysed in view of recent experiments with ultra-cold atoms, nano-structures and nuclei far from the stability valley. For non-zero orbital angular momentum the low energy scattering cross section exhibits dramatic changes depending on the occurrence of either a near resonance or a bound state or the situation in between, that is a bound state at zero energy. Such state is singular in that it has an infinite scattering length, behaves for the eigenvalues but not for the eigenfunctions as an exceptional point and has no pole in the scattering function. These results should be observable whenever the interaction or scattering length can be controlled.

Theoretical calculation of the low-energy scattering cross sections for He-Li2 system

In this paper, the Fuchs potential model and the Close-coupling method are used to calculate the low-energy cross sections for a He-Li2 scattering system. The dependences of total cross section on energies, differential section on angles, and partial wave cross section on quantum number of total angular momentum are discussed . The quantum effect on energy obtained.

Low-energy electron scattering ofNO:Ab initioanalysis of theΣ−3,Δ1, andΣ+1shape resonances in the local complex potential model

We present an ab initio study of elastic scattering and vibrational excitation of $\mathrm{NO}$ by low-energy $(0--2.0\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ electron impact. The low-energy scattering cross sections are dominated by shape resonance contributions associated with the $^{3}\ensuremath{\Sigma}^{\ensuremath{-}}$, $^{1}\ensuremath{\Delta}$, and $^{1}\ensuremath{\Sigma}^{+}$ states of ${\mathrm{NO}}^{\ensuremath{-}}$. Resonance parameters for the three anion states were extracted from an analysis of fixed-nuclei variational (complex Kohn) calculations that employed elaborate trial wave functions. Independent estimates of the resonance parameters were obtained by analytically continuing the results of large-scale coupled-cluster calculations into the plane of complex momentum. The local complex potential model was used to calculate vibrational excitation cross sections, as well as the resonant portion of the vibrationally elastic cross sections. These results were combined with background contributions from the fixed-nuclei calculations to compute elastic and grand total cross sections. Our results capture the essential features of recent measurements of the cross sections, but suggest the need at lower energies for a more sophisticated, nonlocal treatment of nuclear dynamics.

Very low energy electron scattering in C6H5F, C6H5Cl, C6H5Br and C6H5I

Integral and backward scattering cross sections are reported for the scattering of electrons from C6H5F, C6H5Cl, C6H5Br and C6H5I over the energy range between 10 and 20 meV to 10 eV. The measurements were made in transmission experiments using a synchrotron radiation photoionization apparatus with an energy resolution in the incident electron beam of ~3.5 meV (FWHM). The absolute accuracy of the cross sections is limited by experimental difficulties with respect to strong rotationally inelastic forward scattering, due to the dipolar nature of the target molecules. Integral scattering cross sections are found to rise to more than 1500 Å2 at the lowest energies in C6H5F, C6H5Cl and C6H5Br and to more than 2000 Å2 in C6H5I due to an additional contribution from electron attachment. At low energy, both integral and backward scattering cross sections are very similar in C6H5F, C6H5Cl and C6H5Br. Data are interpreted in terms of rotationally inelastic scattering, with values of cross sections essentially dictated by the correspondingly similar dipole moments (1.6-1.7 D) of these three species. The Born model for rotationally inelastic scattering consistently underestimates the experimental cross sections and overestimates the degree of forward scattering. Our data illustrate the limitations of the Born model for the estimation of low-energy scattering cross sections for plasma modelling.

Pion electroproduction from the nucleon near threshold

We investigate the dependence on production amplitude of the low energy scattering cross section for positive pion electroproduction from the nucleon. Calculations based on the threshold approximation to the full amplitudes of Dombey and Read are illustrated and compared to results for the full amplitudes. Inclusion of the momentum-dependent terms yields differential cross sections in the near-threshold region differing from those given by the threshold approximation by no more than 15% at any angle.

Review of the Low Energy Scattering Cross Sections of Deuterium

Review of the Low Energy Scattering Cross Sections of Deuterium

Total Electron Scattering Cross Sections inO2and Ne

A modified Ramsauer technique has been used to measure the total low-energy scattering cross sections of electrons in ${\mathrm{O}}_{2}$ over an energy range from 2.35 to 21 eV, and in Ne over a range from 0.37 to 20 eV. A broad clearly defined bump is observed in the $e\ensuremath{-}{\mathrm{O}}_{2}$ cross section with the maximum occurring between 11 and 12 eV. Both the ${\mathrm{O}}_{2}$ and Ne cross-section data are in good agreement with Br\uche's measurements at energies above 2 eV. Extrapolation of the low-energy Ne data to zero energy, using modified effective-range theory, yields a zero-energy scattering length of $(0.30\ifmmode\pm\else\textpm\fi{}0.03){a}_{0}$, where ${a}_{0}$ is the Bohr radius.

Measurement of Low Energy Scattering Cross Sections for the He–N2 System

Total elastic scattering cross sections for the He–N2 system were measured for relative velocities from 1.68× 104 to 1× 105 cm/sec utilizing the crossed beam technique. An orbiting resonance below the j=0 to 2 transition was observed. Two collimated, aerodynamically intensified molecular beams intersecting at 10° were used. Each beam had a speed distribution comparable to that obtained from mechanical velocity selectors. The scattering center density was determined from a calibration of the detector utilizing a thermal beam source, carefully considering the geometry of the system. Attenuation of the scattering signal due to the background gas was determined without recourse to pressure-gauge readings. One beam was modulated and integrating techniques were used to recover the signal. The time-of-flight technique was used to determine the initial conditions in each beam. The measurements were compared with quantum mechanical calculations performed at the University of Bonn using a LJ (12,6) potential. Generally, the measurements were larger than these calculations, but one resonance was partially resolved.

Total Electron Scattering Cross Sections inO2and Ne

A modified Ramsauer technique has been used to measure the total low-energy scattering cross sections of electrons in ${\mathrm{O}}_{2}$ over an energy range from 2.35 to 21 eV, and in Ne over a range from 0.37 to 20 eV. A broad clearly defined "bump" is observed in the $e\ensuremath{-}{\mathrm{O}}_{2}$ cross section with the maximum occurring between 11 and 12 eV. Both the ${\mathrm{O}}_{2}$ and Ne cross-section data are in good agreement with Br\"uche's measurements at energies above 2 eV. Extrapolation of the low-energy Ne data to zero energy, using modified effective-range theory, yields a zero-energy scattering length of $(0.30\ifmmode\pm\else\textpm\fi{}0.03){a}_{0}$, where ${a}_{0}$ is the Bohr radius.

The low energy scattering cross section of 10B

Measurements of the scattering cross section of 10B relative to that of carbon have been made in the energy range 1–120 keV using 6Li glass neutron detectors on a 50 m flight path of the Harwell electron linac time of flight spectrometer. The measurements carried out at angles of 39°, 65°, 120° and 144° to the incident neutron beam showed no significant differences between the differential scattering cross section measured at the four angles. The total scattering cross section of 10B decreases from a value of 2·97 b at 127 keV to 2·23 at 10 keV, below which it remains constant at an average value of 2·23 ± 0·06 b. This value, when compared with the constant term of 1·95 ± 0·1 b obtained from the total cross section measurements of DiMENT indicates a deviation from the 1/v law for the absorption cross section of (−0·28 ± 0·12) b.

Elastic Scattering of Slow Electrons from Alkali Atoms

The elastic scattering cross sections for slow electrons incident on sodium and potassium are calculated using a model for the polarization potential which was earlier used for cesium. In all the alkalis studied, the low-energy scattering cross sections show an extreme sensitivity to the exact shape of the polarization potential in the region where $r$ is comparable to the atomic radius of the target atom, indicating the necessity of having an accurate description of the polarization term in the total scattering interaction potential. Results are compared with available experimental data. In its application to the alkali atoms, this model yields results which are in good agreement with current experimental results.