Inclusion of a Coulomb interaction potential in a variational model for positronium–helium scattering

2013 ◽  
Vol 91 (2) ◽  
pp. 188-190 ◽  
Author(s):  
Joseph DiRienzi ◽  
Richard J. Drachman
Keyword(s):  
Wave Function ◽  
Short Range ◽  
Scattering Length ◽  
Variational Model ◽  
Coulomb Interactions ◽  
Zero Energy ◽  
Close Coupling ◽  
Helium Atoms ◽  
Coupling Approximation ◽  
Variational Wave

While carrying out investigations on Ps–He scattering it was discovered that it would be possible to improve the results of a previous work on zero-energy scattering of ortho-positronium by helium atoms. The previous work used a model to account for exchange and also attempted to include the effect of short-range Coulomb interactions in the close-coupling approximation. The three terms that were then included did not produce a well-converged result but served to give some justification to the model. Now we improve the calculation by using a simple variational wave function, and derive a much better value of the scattering length. The new result is compared with other computed values, and when an approximate correction due to the van der Waals potential is included the total is consistent with an earlier conjecture.

Dispersion relations and the elastic scattering of electrons by helium atoms

1966 ◽  
Vol 294 (1437) ◽  
pp. 149-159 ◽  
Keyword(s):  
Dispersion Relation ◽  
Elastic Scattering ◽  
Cross Sections ◽  
Scattering Length ◽  
Excitation Threshold ◽  
Zero Energy ◽  
Total Cross Sections ◽  
Scattering Angle ◽  
Helium Atoms ◽  
Microwave Probe

The elastic scattering of electrons by helium is analysed in terms of a dispersion relation for the forward scattering intensity. The zero energy scattering length obtained from this relation agrees well with that derived from application of effective range formulae to observed data on total cross sections and to drift velocity and microwave probe data. It also agrees well with results of exchange-adiabatic calculations. At energies below the excitation threshold these calculations give total and differential cross sections which agree well with observed results except at small scattering angles at energies of 10 eV and below. The dispersion relation gives results agreeing with the calculated at zero scattering angle suggesting that the observed distributions are in error. At energies above the excitation threshold the dispersion relation shows that Born’s first approximation is still considerably in error (by a factor of 2) at zero scattering angle at energies of 300 eV. Experimental data between 100 and 300 eV are consistent with extrapolation to the values given by the dispersion relation for the forward scattered intensity.

scholarly journals Elementary Particle Scattering Lengths and Resonances

1974 ◽  
Vol 27 (1) ◽  
pp. 13
Author(s):  
DC Peaslee
Keyword(s):  
Optical Potential ◽  
Scattering Length ◽  
Compound System ◽  
Zero Energy ◽  
S Wave ◽  
Nucleon System ◽  
Level Shifts ◽  
Wave States ◽  
Scattering Lengths

An investigation is made of the relation between scattering lengths and resonances in a two-nucleon system. For resonances Eo near zero energy the usual determination of an effective optical potential in mesonic atoms is limited, and it is shown here that the scattering length can only be represented usefully as a sum over resonances of the compound system if the condition IEolDI ~ (PDo)! Is satisfied, where D is the average spacing of s-wave states, p the density of target nucleons and Do the Compton volume of the reduced system. This condition is seen to be valid for mr:, nK and KK interactions and these systems are considered in some detail. It is shown that knowledge of the level shifts of each of these examples can help resolve present uncertainties in associated boson structure.

R-matrix calculations of photoionization cross section of Ne-like tungsten

2015 ◽  
Vol 93 (11) ◽  
pp. 1221-1226 ◽  
Author(s):  
Indu Khatri ◽  
Arun Goyal ◽  
Sunny Aggarwal ◽  
A.K. Singh ◽  
Man Mohan
Keyword(s):  
Cross Section ◽  
Energy Levels ◽  
Resonance Energy ◽  
Photoionization Cross Section ◽  
Distorted Wave ◽  
Rydberg Series ◽  
Close Coupling ◽  
R Matrix ◽  
Coupling Approximation ◽  
Wave Methods

The photoionization cross section calculation for the ground state 1s22s22p6 1S (J = 0) of Ne-like W64+ has been performed in the close-coupling approximation using the Dirac–Coulomb R-matrix method. The resonance structures are analysed and described by finding the resonance energy positions of prominent Rydberg series 2s2p6(2S)np 1P0 for W LXV ion. To calculate fine structure energy levels, multi-configuration Dirac–Fock and relativistic distorted-wave methods have been employed. Wherever possible we have compared our work with the available data. The present results will be useful for diagnostics and modeling of plasma in ITER and other fusion devices.

Excitation of Ne VIII by electron impact

1976 ◽  
Vol 54 (20) ◽  
pp. 2019-2023 ◽  
Author(s):  
W. L. van Wyngaarden ◽  
Ronald J. W. Henry
Keyword(s):  
Electron Impact ◽  
Born Approximation ◽  
Experimental Error ◽  
Rate Coefficient ◽  
Impact Excitation ◽  
Rate Coefficients ◽  
Electron Impact Excitation ◽  
Close Coupling ◽  
Coupling Approximation ◽  
Made In

Collision strengths for electron impact excitation of Ne VIII are calculated at 14, 18, and 30 Ry in a 5-state close coupling expansion and the unitarized Coulomb–Born approximation. To assess the importance of exchange and coupling beyond the 5 states, additional calculations are made at 18 Ry in 5-state and 8-state close coupling expansions without exchange. For the 2s–2p excitation, calculations below the 3s threshold at 10.0 Ry are made in a 2-state close coupling expansion at 1.6, 3.2, and 8.0 Ry. In most instances the close coupling method gives results which differ by 15% or less from those of the unitarized Coulomb–Born approximation and by 20–70% from the CBI (Coulomb–Born) results of Bely. Rate coefficients which are calculated from the results obtained in the close coupling approximation agree within experimental error with the experimental results of Kunze and Johnston and Haddad and McWhirter with the exception of the rate coefficient for the 2p → 3d excitation.

scholarly journals Electron-ion recombination in the close-coupling approximation

1992 ◽  
Vol 68 (10) ◽  
pp. 1488-1491 ◽  
Author(s):  
Sultana N. Nahar ◽  
Anil K. Pradhan
Keyword(s):  
Close Coupling ◽  
Coupling Approximation ◽  
Ion Recombination
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