scholarly journals Positron?Lithium Inelastic Scattering with Polarisation Potentials

1991 ◽  
Vol 44 (6) ◽  
pp. 677 ◽  
Author(s):  
M EI-Shabshiry ◽  
SY EI Bakry ◽  
AH Moussa ◽  
MA Abdel-Raouf
Keyword(s):  
Inelastic Scattering ◽  
Cross Section ◽  
Cross Sections ◽  
Excitation Cross Section ◽  
Positronium Formation ◽  
Elastic Channel ◽  
Formation Cross Section ◽  
Positron Energy ◽  
Maximum Value

Positron-lithium inelastic scattering is studied at positron energies ranging from 0�005 to 20 eV using the coupled static model. Two channels are open namely the elastic and positronium formation. The polarisation potentials of the Li atom in the first channel and that of the positronium atom in the second channel are taken into consideration in calculating the corresponding cross sections. The partial cross sections in each channel are calculated for eight values of the total angular momentum (0 ~.e ~ 7). In the elastic channel the total cross section Ull has its maximum value at the lowest energy, and decreases with an increase in positron energy Ki. The total positronium formation cross section has a small dip at 0�1 eV, and maximum value at Ki = 1 �4 eV, and then decreases smoothly with e+ energy. We compare our results with those of Ward et al. (1989) where positronium formation is ignored. The agreement in elastic cross sections improves with e+ energy, while the total collisional cross sections have the closest agreement at 1�0 eV. From this comparison, we find that positronium formation is important in the very low energy region, and the role of the excitation cross section increases steadily with e+ energy.

scholarly journals Monoenergetic Neutrons for Stellar Applications

2009 ◽  
Vol 26 (3) ◽  
pp. 232-236
Author(s):  
M. Mosconi ◽  
M. Heil ◽  
F. Käppeler ◽  
R. Plag ◽  
A. Mengoni ◽  
...  
Keyword(s):  
Inelastic Scattering ◽  
Cross Section ◽  
Cross Sections ◽  
Theoretical Calculations ◽  
Excited Level ◽  
Scattering Cross Section ◽  
Elastic Channel ◽  
Monoenergetic Neutron ◽  
Scattering Cross ◽  
Neutron Beams

AbstractWith modern techniques, neutron-capture cross sections can be determined with uncertainties of a few percent. However, Maxwellian averaged cross sections calculated from such data require a correction (because low-lying excited states are thermally populated in the hot stellar photon bath) which has to be determined by theoretical calculations. These calculations can be improved with information from indirect measurements, in particular by the inelastic scattering cross section. For low-lying levels, the inelastically scattered neutrons are difficult to separate from the dominant elastic channel. This problem is best solved by means of pulsed, monoenergetic neutron beams. For this reason, a pulsed beam of 30 keV neutrons with an energy spread of 7 to 9 keV FWHM and a width from 10 to 15 ns has been produced at Forschungszentrum Karlsruhe using the 7Li(p, n)7Be reaction directly at the reaction threshold. With this neutron beam the inelastic scattering cross section of the first excited level at 9.75 keV in 187Os was determined with a relative uncertainty of 6%. The use of monoenergetic neutron beams has been further pursued at the Physikalisch-Technische Bundesanstalt in Braunschweig, including the 3H(p, n)3He reaction for producing neutrons with an energy of 64 keV.

scholarly journals On the role of longitudinal momenta in high energy hadron-hadron scattering

Open Physics ◽  
2012 ◽  
Vol 10 (4) ◽  
Author(s):  
Igor Sharf ◽  
Andrii Tykhonov ◽  
Grygorii Sokhrannyi ◽  
Maksym Deliyergiyev ◽  
Natalia Podolyan ◽  
...  
Keyword(s):  
Inelastic Scattering ◽  
Cross Section ◽  
Cross Sections ◽  
High Energy ◽  
Momentum Conservation ◽  
Scattering Cross ◽  
Energy Hadron ◽  
Scattering Cross Sections ◽  
Energy Momentum Conservation

AbstractWe demonstrate a new method to calculate inelastic scattering cross-sections, which in contrary to the Regge-based methods takes into account the energy momentum conservation law. It is shown that the main contribution to integral expressing inelastic scattering cross-sections does not come from the multi-Regge domain. In particular, accounting for the longitudinal momenta contribution to virtualities is sufficient and results in the new mechanism of cross-section growth. The reasons for taking into account the sufficiently high number of interference contributions are shown and the approximate method for this purpose is developed. By fitting single free parameter of the model achieved a qualitative agreement of the total and inelastic cross sections with experimental data.

Positronium formation in low-energy positron–helium scattering

1996 ◽  
Vol 74 (7-8) ◽  
pp. 335-342 ◽  
Author(s):  
J. W. Humberston ◽  
P. Van Reeth
Keyword(s):  
Elastic Scattering ◽  
Cross Section ◽  
Cross Sections ◽  
Wave Functions ◽  
Positronium Formation ◽  
Recent Analysis ◽  
S Wave ◽  
Small Magnitude ◽  
Formation Cross Section ◽  
Positron Collisions

Detailed investigations were made of positron collisions with helium atoms in the Ore gap using a two-channel version of the Kohn variational method with very flexible trial wave functions and accurate correlated helium-target wave functions. Accurate values of the s-wave elastic scattering and positronium-formation cross sections are presented, together with preliminary values of the cross sections for s-wave scattering. The s-wave positronium-formation cross section in helium displays a remarkable similarity in both magnitude and energy dependence to the corresponding cross section in positron–hydrogen scattering, with a rapid rise from the positronium-formation threshold and a more gradual rise thereafter. Its small magnitude is consistent with the findings of a recent analysis of experimental measurements of the positronium-formation cross section. Calculations of the s-wave elastic-scattering cross section above and below the positronium-formation threshold reveal a Wigner "rounded step" at the threshold itself.

Role of central depression in the estimation of Coulomb excitation cross-section and absorption effects

2021 ◽  
pp. 2150170
Author(s):  
Monika Goyal ◽  
Rajiv Kumar ◽  
Pardeep Singh ◽  
Raj Kumar Seth ◽  
Rajesh Kharab
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Survival Probability ◽  
Excitation Cross Section ◽  
Coulomb Excitation ◽  
Central Depression ◽  
Excitation Cross Sections

We have investigated the role of central depression parameter on the estimation of survival probability, the Coulomb excitation cross-sections and absorption effects of [Formula: see text] system. The variation in central depression is found to be affecting all the above-mentioned quantities significantly. The survival probability and the Coulomb excitation cross-section are found to be decreasing with increase in [Formula: see text] while the absorption effects are found to be increasing.

Differential ionization in e+–Ar scattering

1996 ◽  
Vol 74 (7-8) ◽  
pp. 468-473 ◽  
Author(s):  
M. Weber ◽  
T. Falke ◽  
W. Raith ◽  
U. Wesskamp
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Time Correlation ◽  
Positron Scattering ◽  
Formation Cross Section ◽  
Positron Energy ◽  
Doubly Charged Ions ◽  
Transfer Ionization ◽  
Low Energies ◽  
Doubly Charged

Differential cross sections of positron scattering from argon atoms leading to singly and doubly charged ions were measured in the angular region from 0° to 120°. These reactions include single and double ionization, transfer, as Ps formation is referred to here, and transfer ionization. The latter is the process of simultaneously ejecting an electron and forming a positronium atom with another electron. The measurement of the time correlation between the detected ion and the scattered particle distinguishes among the reactions, resulting in Ar+ and Ar++, respectively. Measurements were carried out at 30 eV, and, mostly, at 75 eV with an estimated resolution of 2 eV FWHM. The angular acceptance ranged from ±4° to ±2°. Cross sections for single ionization are strongly forward peaked and Ps formation has the most narrow FWHM of ±12° (75 eV incident positron energy) of all. A maximum in the Ps-formation cross section away from 0°, predicted for low energies, was not observed. A very intriguing structure was observed in the transfer-ionization cross section at 45°.

Positronium formation in s-wave positron–hydrogen scattering

1982 ◽  
Vol 60 (4) ◽  
pp. 591-596 ◽  
Author(s):  
J. W. Humberston
Keyword(s):  
Cross Section ◽  
Atomic Hydrogen ◽  
Positronium Formation ◽  
Excitation Threshold ◽  
Matrix Elements ◽  
S Wave ◽  
Formation Cross Section ◽  
Positron Energy ◽  
R Matrix ◽  
A Value

A two channel version of the Kohn variational method is used with trial functions containing up to 120 linear variational parameters to calculate the R-matrix elements and the positronium formation cross section for the scattering of s-wave positrons by atomic hydrogen. Results are obtained in the energy range between the positronium formation threshold and the lowest excitation threshold of the atom. The positronium formation cross section rises very steeply to a value of [Formula: see text] just above the positronium formation threshold and then rises approximately linearly with positron energy to a value of [Formula: see text] just below the excitation threshold. Owing to the weakness of the coupling between the positron and positronium channels, the elastic scattering cross section for the positron continues smoothly across the positronium formation threshold.

Oxygen K near edge structures studied with multiple scattering calculations

1988 ◽  
Vol 46 ◽  
pp. 504-505
Author(s):  
Xudong Weng ◽  
Peter Rez
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Partial Cross Section ◽  
Energy Window ◽  
Edge Structure ◽  
Fine Structures ◽  
Hydrogenic Model ◽  
Electron Energy Loss ◽  
Quantitative Chemical

In electron energy loss spectroscopy, quantitative chemical microanalysis is performed by comparison of the intensity under a specific inner shell edge with the corresponding partial cross section. There are two commonly used models for calculations of atomic partial cross sections, the hydrogenic model and the Hartree-Slater model. Partial cross sections could also be measured from standards of known compositions. These partial cross sections are complicated by variations in the edge shapes, such as the near edge structure (ELNES) and extended fine structures (ELEXFS). The role of these solid state effects in the partial cross sections, and the transferability of the partial cross sections from material to material, has yet to be fully explored. In this work, we consider the oxygen K edge in several oxides as oxygen is present in many materials. Since the energy window of interest is in the range of 20-100 eV, we limit ourselves to the near edge structures.

scholarly journals Saturation effects in SIDIS at very forward rapidities

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
E. Iancu ◽  
A. H. Mueller ◽  
D. N. Triantafyllopoulos ◽  
S. Y. Wei
Keyword(s):  
Inelastic Scattering ◽  
Cross Section ◽  
Cross Sections ◽  
Virtual Photon ◽  
Large Fraction ◽  
Quark Distribution ◽  
High Energy ◽  
Longitudinal Momentum ◽  
Black Disk ◽  
Gluon Saturation

Abstract Using the dipole picture for electron-nucleus deep inelastic scattering at small Bjorken x, we study the effects of gluon saturation in the nuclear target on the cross-section for SIDIS (single inclusive hadron, or jet, production). We argue that the sensitivity of this process to gluon saturation can be enhanced by tagging on a hadron (or jet) which carries a large fraction z ≃ 1 of the longitudinal momentum of the virtual photon. This opens the possibility to study gluon saturation in relatively hard processes, where the virtuality Q2 is (much) larger than the target saturation momentum $$ {Q}_s^2 $$ Q s 2 , but such that z(1 − z)Q2 ≲ $$ {Q}_s^2 $$ Q s 2 . Working in the limit z(1 − z)Q2 ≪ $$ {Q}_s^2 $$ Q s 2 , we predict new phenomena which would signal saturation in the SIDIS cross-section. For sufficiently low transverse momenta k⊥ ≪ Qs of the produced particle, the dominant contribution comes from elastic scattering in the black disk limit, which exposes the unintegrated quark distribution in the virtual photon. For larger momenta k⊥ ≳ Qs, inelastic collisions take the leading role. They explore gluon saturation via multiple scattering, leading to a Gaussian distribution in k⊥ centred around Qs. When z(1 − z)Q2 ≪ Q2, this results in a Cronin peak in the nuclear modification factor (the RpA ratio) at moderate values of x. With decreasing x, this peak is washed out by the high-energy evolution and replaced by nuclear suppression (RpA< 1) up to large momenta k⊥ ≫ Qs. Still for z(1 − z)Q2 ≪ $$ {Q}_s^2 $$ Q s 2 , we also compute SIDIS cross-sections integrated over k⊥. We find that both elastic and inelastic scattering are controlled by the black disk limit, so they yield similar contributions, of zeroth order in the QCD coupling.

Differential cross-section measurements in positron–argon collisions

1996 ◽  
Vol 74 (7-8) ◽  
pp. 505-508 ◽  
Author(s):  
R. M. Finch ◽  
Á. Kövér ◽  
M. Charlton ◽  
G. Laricchia
Keyword(s):  
Elastic Scattering ◽  
Differential Cross Section ◽  
Inelastic Scattering ◽  
Energy Range ◽  
Cross Section ◽  
Cross Sections ◽  
Differential Cross ◽  
Coupling Effect ◽  
Channel Coupling ◽  
Scattering Cross

Differential cross sections for elastic scattering and ionization in positron–argon collisions as a function of energy (40–150 eV) are reported at 60°. Of particular interest is the energy range 55–60 eV, where earlier measurements by the Detroit group found a drop in the elastic-scattering cross section of a factor of 2. This structure has been tentatively attributed to a cross channel-coupling effect with an open inelastic-scattering channel, most likely ionization. Our results indicate that ionization remains an important channel over the same energy range and only begins to decrease at an energy above 60 eV.

Evaporation and Viscous Flow in Triangular Grooves in Micro Heat Pipes

2005 ◽  
Author(s):  
Mulugeta Markos ◽  
Vladimir S. Ajaev ◽  
G. M. Homsy
Keyword(s):  
Cross Section ◽  
Flow Rate ◽  
Cross Sections ◽  
Wedge Angle ◽  
Heat Pipes ◽  
Type Model ◽  
Pressure Gradients ◽  
Maximum Value ◽  
Dry Out ◽  
Micro Heat Pipes

We develop a lubrication type model of a liquid flow in a wedge in the limit of small capillary numbers and negligible gravity. The model incorporates the effects of capillary pressure gradients and evaporation. Steady vapor-liquid interface shapes are found for a range of parameters. In the limit of weak evaporation the flow is the same in all cross-sections and can be controlled by changing the wedge angle. We find the wedge angle that results in the maximum value of the flow rate for a given contact angle. For high evaporation rates, both the flow rate and the amount of liquid in each cross-section along the wedge decrease until the point of dry-out is reached. The location of the dry-out point is studied as a function of evaporation. Practical suggestions about optimization of micro heat pipes are given.

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