Walter F. Huebner

Fits to new calculations of photoionization cross sections for low-Z elements

Abstract Analytical approximations to results of new calculations of partial (i.e. by subshell) photoionization cross sections of elements (2

Solar neutrinos. IV. Effect of radiative opacities on calculated neutrino fluxes

The effect of radiativc opacities on the predicted capture rate for the / sup 37/Cl solar neutrino experiment is investigated with the aid of new opacities obtained from an improved Los Alamos code. (auth)

Is the metal contribution to the astrophysical opacity incorrect

Numerical tests by Simon have indicated that an arbitrary increase in the metal (atomic number Z>2) contribution to the opacity by a factor of 2 to 3 leads to Cepheid models that, in some aspects, are in better agreement with observations than models using the standard opacity. We show that such a large increase in opacity is incompatible with atomic physics.

Electron-electron interaction in energy level determination☆

Abstract Electron-electron Coulomb interaction energies are expressed in terms of relativistic one-electron orbitals. The average electron-electron interaction energy, τ, is obtained and tabulated for Z = 1 and 30, for electron configurations in j-j coupling, from relativistic, hydrogenic F(0) and nonrelativistic, hydrogenic G(k) Slater integrals, with k ≤ 56. Coefficients T(nljm, n′l′m′) for the angular integrals in j-j coupling for f-electro ns are calculated. A relationship to obtain these coefficients directly from the corresponding coefficients in L-S coupling is given. A perturbation method is described to obtain quickly approximate binding energies for the electrons in ions in their ground state, and for the electrons in ions and neutral atoms in excited states, from known binding energy data of neutral atoms corrected for the electron-electron interaction energy.

Group mean emissivities and opacities of high temperature SiO2

Abstract Absorption and extinction coefficients of SiO 2 have been calculated using a mean ion model but with the most important singly and multiply excited states of the dominant ionic species considered explicitly. Free-free, bound-free, bound-bound, and scattering are taken into account. Densities range from 10 -6 to 10 3 g cm -3 and temperatures range from 30 to 10 keV. Emissivities are obtained from detailed balance. Group means are given for some representative cases.

On the calculation of scattering cross sections from absorption cross sections

Abstract A dispersion-type relation between photon scattering and absorption cross sections is derived. It is shown that the relation gives the correct scattering cross section in the low and high frequency limits, and is consistent with the Kramers-Heisenberg formula in the vicinity of a resonance. The practical application of the relation is illustrated by calculations of the scattering cross section and refractive index of He and Ne at STP and dry air at 1200°K from known absorption cross section data. The method is useful for obtaining scattering cross sections, polarizabilities, and refractive indices at elevated temperatures.

SOME ESTIMATES OF THE RADIATIVE ROSSELAND MEAN OPACITY.

Abstract The effect of atomic number Z on the Rosseland mean opacity is presented in graphic form for a large range of temperatures and densities. This permits a rapid determination of the dominant process and, in many cases, greatly simplifies the calculation of a good approximation of the Rosseland mean opacity.

Photoelectric cross sections for ions scaled from their neutral atoms

Abstract Removal of outer electrons from an atom does not significantly change the potential and wave functions over the region where the wave function of the remaining bound electrons is large. This explains why the partial cross sections of an ion are similar to those of its neutral atom but truncated at the ions threshold. Scaling by the wave-function-effective-Z can significantly improve the accuracy of the ion partial cross sections.

Discrepancy in the CNO opacity bump resolved. [Application to stellar problems]

The discrepancy between the Los Alamos and the Carson opacities for mixtures containing metals at low densities around a temperature of 10/sup 6/ K (the CNO bump) has been investigated and resolved. The bump in the Carson opacities arises from a misapplied correction to the atomic level occupancies. Results from a modified Carson opacity program now show much closer agreement with the Los Alamos opacities. There is no evidence for a CNO bump. 14 references, 2 tables.

Review and summary of opacity calculations

Abstract An outline is presented of relevant methods and theories emphasizing the main contributions to Rosseland mean opacities in widely differing temperature and compression ranges for widely different elements and mixtures.