Robert D. Cowan

Approximate relativistic corrections to atomic radial wave functions

The mass-velocity and Darwin terms of the one-electron-atom Pauli equation have been added to the Hartree-Fock differential equations by using the HX formula to calculate a local central field potential for use in these terms. Introduction of the quantum number j is avoided by omitting the spin-orbit term of the Pauli equation. The major relativistic effects, both direct and indirect, are thereby incorporated into the wave functions, while allowing retention of the commonly used nonrelativistic formulation of energy level calculations. The improvement afforded in calculated total binding energies, excitation energies, spin-orbit parameters, and expectation values of rm is comparable with that provided by fully relativistic Dirac-Hartree-Fock calculations.

Theoretical Calculation of Atomic Spectra Using Digital Computers

For an arbitrary electron configuration l1n1l2n2l3n3⋯, analytical expressions are derived for the energy-matrix coefficients of the electrostatic-interaction parameters Fk(li,lj) and Gk(li,lj) and of the spin–orbit parameters ζ(li). A computer program is described which calculates decimal values of these coefficients for any configuration with less than five open subshells, starting from only a table of the terms, parents, and coefficients of fractional parentage for each open subshell lini. Given also a set of values of the parameters, the program evaluates and diagonalizes the energy matrices to obtain the eigenvalues and eigenvectors of the states belonging to this configuration. If so specified, the program does the above for two configurations of opposite parity, differences eigenvalues to obtain wavelengths for dipole transitions, and from the eigenvectors computes line strengths and (given an absolute value for the reduced dipole matrix element) transition probabilities.

Calculation of the Detonation Properties of Solid Explosives with the Kistiakowsky‐Wilson Equation of State

The Kistiakowsky‐Wilson equation of state, pVg = RT(1+xeβx), where x = k/Vg(T+θ)α, for the gaseous detonation products of solid explosives has been re‐examined in the light of new experimental data on detonation pressure and on the variation of detonation velocity D with loading density ρ0 for several RDX/TNT mixtures. The value β = 0.30 used in the past is too high to match the observed slopes of the D—ρ0 curves. The old value α = 0.25 is too small to match the experimental Chapman‐Jouguet pressure of most of these explosives, but too large to match the pressure of pure TNT. A suitable compromise for the explosives considered is α = 0.5, β = 0.09, θ = 400°K.

Coupling Considerations in Two-Electron Spectra*

The energy level structure, relative line strengths, and Lande g factors of two-electron configurations are discussed for four important types of pure coupling: LS, LK(Ls), jK(jl), and jj. Transitions from one type of coupling to another are discussed in detail, the configuration pf being used as an example. The appropriateness of LS- and jj-coupling notation in two-electron spectra is quite limited for atoms of medium atomic weight, where nearly all excited configurations show a strong tendency toward pair (LK to jK) coupling. For other atoms, pair coupling occurs mainly for high values of orbital angular momentum of the excited electron: the coupling may then be near LK for small values of the principal quantum number of this electron, approaching pure jK as this quantum number increases. Either LK or jK notation can serve unambiguously to identify levels throughout the range of intermediate pair couplings, but neither will correctly designate the nature of the quantum states in all cases because of exchanges of the L (and of the j) compositions of certain states which occur as the coupling conditions change from pure LK to pure jK. Examples are discussed from the spectra of N, P, Ge, and the rare gases.

X‐ray spectra from a gas‐puff z‐pinch device

X‐ray emission was used to diagnose the plasma formation in a gas‐puff pulsed‐discharge device. X‐ray pinhole images were collected simultaneously with x‐ray spectra from Ar and Kr gases. X rays were emitted from z‐pinched regions (50–100 μm in diameter) along a collinear track formed by the plasma implosion of a hollow gas jet. Spectral analysis indicated Ar plasma formation with electron densities of ∼2×1021 cm−3. The Ar plasma temperature was ∼1 keV, based on a collisional‐radiative transport model. Li‐like satellite lines were classified in Ar XVI with atomic structure calculations. The Kr x‐ray spectrum (6–8‐A region) was dominated by Ne‐like Kr XXVII lines. New spectral transitions were classified in Na‐like Kr XXVI and F‐like Kr XXVIII. The wavelength calibrations in the Kr spectrum were obtained from exploded‐Al‐wire plasma generated in coincidence with the plasma implosion formed in the puff gas.

Theoretical Study of pm–pm −1 l Spectra*

Theoretical calculation of energy levels and spectra ab initio are described for transitions of the type pm–pm−1l, especially 3pm–3pm−13d transitions in the Ar i and Cl i isoelectronic sequences. Strong changes of wavefunction composition occur in going from neutral atoms to ions as a result of collapse of the 3d wavefunction; for m = 2 and 6 these take the form of coupling changes, and for m = 3–5 they take the form of changes of parentage composition. Abnormally low Ti v 3p6–3p54d intensities are explained as an interference effect in evaluation of the dipole radial integral.

Isoelectronic sequence fits to configuration-averaged photoionization cross sections and ionization energies

Abstract Hartree-Fock wave functions have been used to calculate configuration-averaged photonization cross sections and ionization energies for orbitals 1 s ⩽ nl ⩽ 5 g in He-like through Al-like isoelectronic sequences. The photoionization cross sections have been fitted as a function of the nuclear charge, Z , and photon energy, X , in threshold units, with average error of less than 10%. The ionization energies have been fitted as a function of Z with errors of less than 0.5%.

Fluorine isoelectronic sequence

Energy levels and wavelengths of lines of the fluorine isoelectronic sequence are given for the ions K xi through Co xix. The energy levels are derived from spectra obtained by use of a grazing-incidence 3-m spectrograph with a low-inductance vacuum spark as a source. The experimental results are compared with theoretical values obtained by Hartree–Fock-type computations.

Spectra of solar flares from 8.5 Å to 16 Å

X-ray spectra of solar flares in the spectral range from 8.5 Å to ∼ 16 Å have been obtained from a Naval Research Laboratory crystal spectrometer flown on the sixth Orbiting Solar Observatory (OSO-6). A list of emission features is presented and tentative identifications of some of the features are suggested. The time-behavior of the emission lines during flares is discussed, and the possibility of determining electron densities in flare plasmas using density sensitive lines of highly ionized iron is considered. Approximate calculations are performed for a density sensitive line of Fexxii.

High resolution X-ray spectra of solar flares. V - Interpretation of inner-shell transitions in Fe XX-Fe XXIII

We discuss high-resolution solar flare iron line spectra recorded between 1.82 and 1.97 A by a spectrometer flown by the Naval Research Laboratory on an Air Force spacecraft launched on 1979 February 24. The emission line spectrum is due to inner-shell transitions in the ions Fe XX-Fe XXV. Using theoretical spectra and calculations of line intensities obtained by methods discussed by Merts, Cowan, and Magee, we derive electron temperatures as a function for time of two large class X flares. These temperatures are deduced from intensities of lines of Fe XXIII, Fe XXII, and Fe XXIV. Previous measurements by us have involved only lines of Fe XXIV and Fe XXV. We discuss the determination of the differential emission measure between about 12 x 10/sup 6/ K and 20 x 10/sup 6/ K using these temperatures. The possibility of determining electron densities in flare and tokamak plasmas using the inner-shell spectra of Fe XXI and Fe XX is discussed. We also discuss recent theoretical work by Mewe and Schrijver based on atomic data of Grineva, Safronova, and Urnov.