Cross Sections For Na Research Articles

Basic features of Ne*-HX (X = Cl, Br) chemi-ionization reactions.

Total and partial ionization cross sections for Ne*(3P2,0)–HX (X = Cl, Br) are presented in a comparative way as a function of the collision energy between 0.02–0.5 eV. New mass spectrometric data on Ne*–HBr chemi-ionization are discussed and analyzed with already published data on Ne*–HCl, highlighting similarities and differences of the collisional stereodynamics of the two systems. Basic features of the interaction potentials, driving reactive collisions, suggest that reaction channels, leading to the formation of parent HX+ ions in the ground and excited electronic state and to the formation of associated NeHX+ ions as well as of NeH+ proton transfer species, are selectively opened within angular cones exhibiting different orientation and acceptance.

Effects of in-medium NN cross section and density distribution on the reaction cross sections of Ne, Mg, and O isotopes with C12 at 1 GeV

The nucleus-nucleus reaction cross sections of $^{18--34}\text{Ne},^{20--36}\text{Mg},^{16--24}\text{O}+^{12}\mathrm{C}$ at one GeV/u are calculated in the Glauber theory using different models of the nucleon-nucleon ($NN$) cross sections and nuclear densities. For in-medium effects, we consider the phenomenological (Ph), geometrical Pauli (GP), and modified combined (MC) models for the $NN$ reaction cross section. For the density distributions, we used the Sao Paulo (SP), Skyrme-Hartree-Fock (SHF), and the angle-averaged deformed Fermi (DF) densities. The results are compared with experiments as well as other theoretical calculations. It is found that the data can, generally, be described by using the Ph and GP models for in-medium effects with the SP density, which, on the other hand, predicted smaller radii. A satisfactory explanation of the experimental data is obtained by using more realistic densities such as SHF and DF with realistic radii, and the MC model for medium modifications, which involve the combined effect of the phase variation, higher momentum transfer components, and Pauli blocking of the $NN$ amplitude. The in-medium Ph and GP models when used with realistic densities, cannot describe the data at 1 GeV.

Inelastic processes inNa+-Ne,Na+-Ar,Ne+-Na, andAr+-Na collisions in the energy range 0.5–14 keV

Absolute cross sections for charge-exchange, ionization and excitation in Na$% ^{+}-$Ne and Na$^{+}-$Ar collisions were measured in the ion energy range $% 0.5-10$ keV using a refined version of a capacitor method, and collision and optical spectroscopy methods simultaneously in the same experimental set-up. Ionization cross sections for Ne$^{+}-$Na and Ar$^{+}-$Na collisions are measured at the energies of $2-14$ keV using a crossed-beam spectroscopy method. The experimental data and the schematic correlation diagrams are used to analyze and determine the mechanisms for these processes. For the charge-exchange process in Na$^{+}$ $-$Ar collisions two nonadiabatic regions are revealed and mechanisms responsible for these regions are explained. Structural peculiarity on the excitation function for the resonance lines of argon atoms in Na$^{+}$ $-$Ar collisions are observed and the possible mechanisms of this phenomenon are explored. The measured ionization cross sections for Na$^{+}-$Ne and Ne$^{+}-$Na collisions in conjunction with the Landau-Zener formula are used to determine the coupling matrix element and transition probability in a region of pseudo-crossing of the potential curves.

Positron and electron-impact multiple-ionization

We present positron-impact multiple (single to quintuple) and total ionization cross sections of Ne, Ar, Kr, and Xe, covering an extended energy range from 50 eV to 7 keV. We improve on previous calculations of the ionization thresholds by adding the mean kinetic energy transferred to the target electrons. In this way the thresholds compare rather well with the experimental appearance energies for the different k-fold ionization cross sections. Present results include not only the novel energy threshold at low energies but also the post-collisional contribution at high energies. We performed a quite complete particle–antiparticle comparison by including our positron-impact results, new calculations for electron-impact ionization including the threshold correction, and a detailed compilation of experimental data. Present positron-impact multiple ionization cross sections are the first ones in such an extended energy region.

Configuration-interaction relativistic-many-body-perturbation-theory calculations of photoionization cross sections from quasicontinuum oscillator strengths

Many applications are in need of accurate photoionization cross sections, especially in the case of complex atoms. Configuration-interaction relativistic-many-body-perturbation theory (CI-RMBPT) has been successful in predicting atomic energies, matrix elements between discrete states, and other properties, which is quite promising, but it has not been applied to photoionization problems owing to extra complications arising from continuum states. In this paper a method that will allow the conversion of discrete CI-(R)MPBT oscillator strengths (OS) to photoionization cross sections with minimal modifications of the codes is introduced and CI-RMBPT cross sections of Ne, Ar, Kr, and Xe are calculated. A consistent agreement with experiment is found. RMBPT corrections are particularly significant for Ar, Kr, and Xe and improve agreement with experimental results compared to the particle-hole CI method. The demonstrated conversion method can be applied to CI-RMBPT photoionization calculations for a large number of multivalence atoms and ions.

Analysis of reaction cross sections of Ne and Mg isotopes at 240 MeV/u in the Dirac-Brueckner approach and Glauber model

Within a relativistic effective complex nucleon-nucleon interaction derived by solving the Dirac-Brueckner-Bethe-Goldstone equation, locally, starting from the one-boson-exchange potential (OBEP) as a bare NN interaction, the optical potentials and reaction cross sections of the 20-36Ne , 24-38Mg + 12C reactions, recently observed at 240MeV/u , are calculated. The proton and neutron density distributions of target and projectile are derived from Skyrme-Hartree-Fock calculations, employing SKRA and SKM* interactions. A comparison between the experimental data as well as recent theoretical calculations of Horiuchi et al. (Phys. Rev. C 86, 024614 (2012)) and Panda et al. (Mod. Phys. Lett. A 29, 1450013 (2014)) show that the data are well reproduced by the present relativistic calculations.

Comparison of the electron impact experimental and theoretical fourfold differential cross sections for Ne and CH4

New measurements of the electron impact (e,3-1e) fourfold differential cross section for double ionization of isoelectronic atomic and molecular targets, namely Ne and CH4, are reported. The measurements are performed at intermediate incident energy and a different energy range for the pair of ejected electrons. We compare the experimental results with the predictions of a recently developed kinematical model (Lahmam-Bennani et al 2010 J. Phys. B: At. Mol. Opt. Phys. 43 105201), which can explain the appearance of the structures related to the second-order mechanism (such as TS2). Some of the data are compared with the predictions of the first and second Born models, showing mixed agreement. Moreover, the targets are isoelectronic hence the difference between the behaviour of the cross sections is qualitatively discussed in terms of the molecular structure influence over the ionization process.

Study of the $^{15}$O$(2p,\gamma )^{17}$Ne Cross Section by Coulomb Dissociation of $^{17}$Ne for the $rp$ Process of Nucleosynthesis

The O-15(2p, gamma)Ne-17 cross section has been studied by the inverse reaction, the Coulomb dissociation of Ne-17. The experiment has been performed at the GSI. The Ne-17 excitation energy prior to decay has been reconstructed by using the invariant-mass method. The preliminary differential and integral Coulomb dissociation cross sections (sigma(Coul)) have been extracted, which provide a photoabsorption (sigma(photo)) and a radiative capture cross section (sigma(cap)). Additionally, important information about the Ne-17 nuclear structure will be obtained. The analysis is in progress.

Calculation of Deexcitation Probability of Ne(3P2) by Ar for the Case E>>D

The deexcitaion probability calculation of the total Penning ionization cross section for Ne(3P2) by Ar has been made at collisional energy 38.1 meV. The comparison of deexcitationcross sections, polarizability, α/β , deexcitation probability, {IP(M)/IP(Ne*)}1/2 and the welldepth of interaction potentials for Ne(3P2) by Ar for the case E >> D has been made.DOI: http://dx.doi.org/10.3126/jncs.v30i0.9335Journal of Nepal Chemical Society Vol. 30, 2012 Page: 52-55 Uploaded date: 12/16/2013

Measurement of the reaction18O(α,n)21Ne

Background: The reaction ${}^{18}$O${(\ensuremath{\alpha},n)}^{21}$Ne is a part of the reaction chains leading to the production of ${}^{19}$F and ${}^{22}$Ne during He burning in low-mass and massive AGB stars, respectively. Additionally, it has been observed as a strong background source in the measurement of other $(\ensuremath{\alpha},n)$ reactions.Purpose: Previously low-energy ${}^{18}$O${(\ensuremath{\alpha},n)}^{21}$Ne cross section data have only been available in a non-peer-reviewed form. An improved measurement of this reaction has been done to both clarify its astrophysical influence as well as to provide background yield data for future $(\ensuremath{\alpha},n)$ experiments.Method: The ${}^{18}$O$(\ensuremath{\alpha},{n}_{(0+1)})$ reaction has been measured with a moderating neutron detector. In addition the $(\ensuremath{\alpha},{n}_{1}\ensuremath{\gamma})$ channel has been measured independently by observation of the characteristic 350.7 keV $\ensuremath{\gamma}$ transition in ${}^{21}$Ne. The reaction cross section at energies above ${E}_{\ensuremath{\alpha}}=1100$ keV was determined by a simultaneous $R$-matrix fit to both channels. The strengths of the two lowest-energy resonances at ${E}_{\ensuremath{\alpha}}=959$ keV and ${E}_{\ensuremath{\alpha}}=1066$ keV were analyzed separately using individual Breit-Wigner fits.Results: The cross section of both reaction channels, ${}^{18}$O${(\ensuremath{\alpha},{n}_{0})}^{21}$Ne and ${}^{18}$O${(\ensuremath{\alpha},{n}_{1}\ensuremath{\gamma})}^{21}$Ne, was determined from the threshold energies at 851 keV and 1280 keV, respectively, to 2300 keV. A new reaction rate has been deduced for the temperature range of 0.1 GK to 10 GK. A previously reported resonance at ${E}_{\ensuremath{\alpha}}=888$ keV is explained as background from the contaminant reaction ${}^{17}$O${(\ensuremath{\alpha},n)}^{20}$Ne.Conclusions: In general, our reaction rate is slightly lower than the reaction rates in recent compilations. At temperatures below 0.2 GK the present rate is significantly lower because it could be shown that the lowest reported resonance is background from the reaction ${}^{17}$O${(\ensuremath{\alpha},n)}^{20}$Ne that has been wrongly assigned to ${}^{18}$O${(\ensuremath{\alpha},n)}^{21}$Ne.

Positron scattering from noble gases

We have extended the nonrelativistic convergent close-coupling (CCC) method to the calculation of positron scattering from noble gases within the single-centre approximation. Good agreement is found with the available measurements of total cross sections and elastic differential cross sections for Ne, Ar, Kr and Xe.

Glauber-model analysis of total reaction cross sections for Ne, Mg, Si, and S isotopes with Skyrme-Hartree-Fock densities

A systematic analysis is made on the total reaction cross sections for Ne, Mg, Si, and S isotopes. The high-energy nucleus-nucleus collision is described based on the Glauber model. Using the Skyrme-Hartree-Fock method in the three-dimensional grid-space representation, we determine the nuclear density distribution for a wide range of nuclei self-consistently without assuming any spatial symmetry. The calculated total reaction cross sections consistently agree with the recent cross section data on Ne$+^{12}$C collision at 240$A$\,MeV, which makes it possible to discuss the radius and deformation of the isotopes. The total reaction cross sections for Mg$+^{12}$C, Si$+^{12}$C and S$+^{12}$C cases are predicted for future measurements. We also find that the high-energy cross section data for O, Ne, and Mg isotopes on a $^{12}$C target at around 1000\,$A$MeV can not be reproduced consistently with the corresponding data at 240\,$A$MeV.

Effectiveness of projectile screening in single and multiple ionization of Ne by B2+

Pure multiple ionization cross sections of Ne by B${}^{2+}$ projectiles have been measured in the energy range of 0.75 to 4.0 MeV and calculated using the continuum distorted wave-eikonal initial state approximation. The experiment and calculations show that the ionization cross sections by B${}^{2+}$, principally for the production of highly charged recoils, is strongly enhanced when compared to the bare projectile with the same charge state, He${}^{2+}$, at the same velocities.

CDW-EIS calculations for multiple ionization of Ne, Ar, Kr and Xe by the impact of H+ and He+, including post-collisional electron emission

We present theoretical single to quintuple ionization cross sections for Ne, Ar, Kr and Xe bombarded by H+ and He+. Post-collisional contributions due to Auger-like processes are taken into account using recent photoionization data. The present continuum distorted wave-eikonal initial state (CDW-EIS) and first Born approximation results are compared with the experimental data available in the energy range of 50–10 000 keV amu−1 for H+ on Ne and Ar, and 50–1000 keV amu−1 for the other cases. In general, the combination of the CDW-EIS with the post-collisional branching ratios describes well the multiple ionization data above 300 keV amu−1, showing a clear tendency to coalesce with the first Born approximation at high energies. The surprising result of this work is the good performance of the first Born approximation which describes rather well the experimental data of double and triple ionization, even in the intermediate energy range (50–300 keV amu−1), where direct ionization is the dominant contribution.

Calculations of total ionization cross sections of Ne, Ar, Kr, and Xe atoms in the born approximation allowing for electron perturbations in the continuous spectrum

Electron impact ionization cross sections of Ne, Ar, Kr, and Xe atoms are numerically calculated. The electron perturbation in the continuous spectrum in the target field is taken into account. The matrix elements are calculated in many-electron, nonrelativistic approximation with allowance for the superposition of configurations and relaxation effect. The radial part of the electron wave function in the continuum is calculated by solving the single-configuration Hartree-Fock equation. The wave functions of electrons in the continuum are orthogonalized with respect to the core orbital functions. The calculated cross sections are compared to the experimental data and calculations made using the plane-wave Born approximation and that involving generalized oscillator strengths.

Tilting oil-water contact in the chalk of Tyra Field as interpreted from capillary pressure data

Abstract The Tyra Field in the central North Sea is located in Palaeogene and Upper Cretaceous chalk. It contains a natural gas zone underlain by an oil leg. Based on analysis of logs and core data from ten wells drilled prior to the field being put into production, normalized water saturation depth-trends from logs were compared with normalized water saturation depth-trends predicted from capillary pressure core data. The ten wells lie close to a SW–NE cross section of the field. For the gas–oil contact, a free contact measured in one well corresponds to a practically horizontal contact interpreted from logging data in the remaining wells. A westerly dipping oil–water contact was found from logging data. Comparison of the depth-wise trends in normalized water saturation among the different wells indicates a regional pattern: in the western side of the field, the trends correspond to a situation of imbibition, where the free water level overlies an interval of residual oil, whereas in the eastern part of the field, the depth-wise trends in normalized water saturation correspond to a situation of drainage. The free water level apparently dips to the east due either to hydrodynamic action or to pressure inequilibrium in the aquifer following tectonic tilting.

Nonperturbative calculations of double photoionization of Ne: AnRmatrix with pseudostate-convergence study

The $R$ matrix with pseudostate (RMPS) method has been employed to perform nonperturbative calculations of the total cross sections for single-photon double photoionization of ground-state Ne. A series of calculations was performed in which the number of pseudostates included in the close-coupling expansion was varied. Within the constraints of currently available massively parallel computers, we were able to achieve reasonably good convergence of the double photoionization cross section for Ne. The final RMPS results in both the length and the velocity gauges are compared to double photoionization cross sections determined from many-body perturbation-theory calculations and synchrotron measurements.

Ionization in fast atom-atom collisions: The influence and scaling behavior of electron-electron and electron-nucleus interactions

We report cross sections for ionization of He coincident with electron loss from He, Li, C, O, and Ne pro jectiles. For He, Li, C, and O pro jectiles, the cross sections were measured directly, while the Ne cross sections were obtained by transforming results for He pro jectiles colliding with Ne. We find that, at energies of about 100-500 keV/u, neutral pro jectiles can ionize a He target almost as effectively as a charged pro jectile. The contribution to ionization due to electron-electron interactions is found to scale with the number of available pro jectile electrons. Comparing ionization by the bound electrons on projectiles to ionization by free electrons, we find the cross sections for ionization by bound electrons are systematically smaller than those for free electrons.

High-resolution absolute photoabsorption cross sections for Ne in the 1s2s and 1s2p resonant double excitation

The high-resolution absolute photoabsorption cross sections with an absolute photon energy scale for Ne 1s2p/1s2s double excitation in the energy region of 900–940 eV have been measured using a multi-electrode ionization chamber and monochromatized synchrotron radiation. The Ne [1s2p](3,1P)nln′l′ doubly excited states observed in the energy range of 900–920 eV are analysed with the aid of theoretical calculations based on the multiconfiguration Dirac–Fock method. The second strongest peak in this energy region is assigned to be [1s2p](3P)3p4p.

Ionization rates for He, Ne, and Ar subjected to laser light with wavelengths between 248.6 and390nm

Using the $R$-matrix Floquet approach, we have investigated multiphoton single ionization of helium, neon, and argon subjected to laser light with a wavelength between 248.6 and $390\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. For a wavelength of $390\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, we have investigated ionization rates for Ne and Ar at intensities up to $2.5\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$. In this intensity regime, the ionization rates no longer follow the multiphoton ${I}^{N}$ power law. At an intensity of $2\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$, a tunneling model approximates the Ar ionization rates within a factor 3, but the differences are much larger for Ne. The ionization rates at $390\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ are affected by intermediate resonances, with these resonances both enhancing and inhibiting ionization. Multiphoton ionization cross sections for Ne and Ar at $248.6\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ have also been determined.