Papers by Thomas Gorczyca
Physical review, Feb 21, 2023
arXiv (Cornell University), Nov 14, 2018
International audienceAstrophysics advances, in part, through laboratory astrophysics studies of ... more International audienceAstrophysics advances, in part, through laboratory astrophysics studies of the underlying processes controlling the observed properties of the Cosmos. These studies encompass both theoretical and experimental research. Robust support for laboratory astrophysics is critically needed to maximize the scientific return of astronomical observations
Physica Scripta, 2021
As a part of the investigation of the entire Si isonuclear sequence for x-ray spectral diagnostic... more As a part of the investigation of the entire Si isonuclear sequence for x-ray spectral diagnostics, we focus on the Li-like Si11+ ion, a stable component that features prominently in x-ray astrophysical spectra. We perform R-matrix calculations for the photoabsorption cross section of Si11+ including relativistic contributions via the use of a Breit-Pauli Hamiltonian. Relativistic effects—predominantly spin-orbit splitting of resonances and mass-velocity and one-body Darwin global shifts of energies —are shown to be tractable and of importance for accuracy in x-ray spectral modeling data banks.
Atoms, 2021
I met Oleg Zatsarinny in 2001, and he then worked with me at Western Michigan University for two ... more I met Oleg Zatsarinny in 2001, and he then worked with me at Western Michigan University for two years. From 2003 to 2013, we were coauthors of 15 papers on theoretical atomic physics, and maintained a friendly relationship over twenty years, meeting and socializing often at conferences. Further elaboration follows below.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2021
Endofullerene photoionization of open-shell N@C60 is investigated using a coupled-channel, correl... more Endofullerene photoionization of open-shell N@C60 is investigated using a coupled-channel, correlated R-matrix approach with additional modifications for a finite spherical-shell fullerene potential. Particular focus is on the initial-state dependence of the photoionization cross section. Comparisons show significant differences between the 1s 22s 22p 3(4S) initial state and the metastable 2D and 2P states, as well as strong confinement oscillations.
Journal of Physics: Conference Series, 2020
Synopsis The effect of inner-shell excited channels on outer-shell photodetachment is investigate... more Synopsis The effect of inner-shell excited channels on outer-shell photodetachment is investigated using a correlated and coupled-channel R-matrix method. The simplest multishell negative ion of Li− is treated near the 1s ionization threshold to determine strong”hole-state” continuum coupling with the direct photodetachment channels.
Journal of Low Temperature Physics, 2018
The neutrino mass can be extracted from a high statistics, high resolution calorimetric spectrum ... more The neutrino mass can be extracted from a high statistics, high resolution calorimetric spectrum of electron capture in 163 Ho. In order to better understand the shape of the calorimetric electron capture spectrum, a second isotope was measured with a close to ideal absorber-source configuration. 193 Pt was created by irradiating a 192 Pt-enriched platinum foil in a nuclear reactor. This Pt-in-Pt absorber was designed to have a nearly ideal absorber-source configuration. The measured 193 Pt calorimetric electron-capture spectrum provides an independent check on the corresponding theoretical calculations, which have thus far been compared only for 163 Ho. The first experimental and theoretically-calculated spectra from this 193 Pt-in-Pt absorber are presented and overlaid for preliminary comparison of theory with experiment.
The Astrophysical Journal Supplement Series, 2001
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Physica Scripta, 2021
We describe a joint experimental and theoretical investigation on oxygen double photoionization—t... more We describe a joint experimental and theoretical investigation on oxygen double photoionization—the emission of two electrons from atomic oxygen following single photon absorption. High-resolution experimental measurements were performed at the Advanced Light Source, revealing sharp resonance structure superimposed on the more familiar Wannier-like, nearly-linear background. These resonance features are attributed to ionization-plus-excitation Feshbach resonances embedded in the double ionization continuum, doubly-excited states that lie above the double-ionization threshold. Such features are absent in the double photoionization cross section of He, or other quasi-two-electron systems, for which the doubly-ionized atomic core remains inert. For a corresponding theoretical analysis, the R-matrix with pseudostates (RMPS) method was invoked by calculating final-state, two-electron resonances-plus-continua wavefunctions and corresponding single-photon absorption cross sections. Overall...
Submitted for the DAMOP17 Meeting of The American Physical Society Wavepacket dynamics in the sca... more Submitted for the DAMOP17 Meeting of The American Physical Society Wavepacket dynamics in the scattering of hydrogen anions off vicinally nano-stepped metal surfaces1 JOHN SHAW, HIMADRI CHAKRABORTY, Northwest Missouri State University, Maryville, MO, DAVID MONISMITH, Software Maintenance Group, Tinker AFB, Oklahoma, USA — We study the electron dynamics in monocrystalline Cu, Au and Pd surfaces [1] with stepped vicinal structures modeled in a Kronig-Penney scheme [2]. The unoccupied bands of the surface is resonantly excited via the charge transfer interaction of the surface with a moving hydrogen anion. The interaction dynamics are simulated in a quantum mechanical wavepacket propagation approach [3] that used parallel computations [4]. The survival probability of the interacting ion is calculated as well as the electron probability density at all times during the interaction. Animated videos are produced of the electron probability density which show that, when the electron is tran...
The ISMabs model considers the absorption effects of the ISM in observed spectra in the following... more The ISMabs model considers the absorption effects of the ISM in observed spectra in the following way I obs (E) = e-τ I source (E) where I obs (E) is the observed X-ray intensity, I source (E) is the X-ray emitted intensity by the X-ray source and e-τ is the absorption coefficient. The optical depth is defined as τ = Σ σ i (E)N i where σ i (E) and N i are the cross sections and the ionic column densities, respectively. The ionic column densities are the model free parameters. All the cross sections are loaded and cached to reduce computational overhead while data fitting. Redshiftis also included as a model parameter.
The Astrophysical Journal, 2015
We present an X-ray absorption model for the interstellar medium, to be referred to as ISMabs, th... more We present an X-ray absorption model for the interstellar medium, to be referred to as ISMabs, that takes into account both neutral and ionized species of cosmically abundant elements, and includes the most accurate atomic data available. Using high-resolution spectra from eight X-ray binaries obtained with the Chandra High Energy Transmission Grating Spectrometer, we proceed to benchmark the atomic data in the model particularly in the neon K-edge region. Compared with previous photoabsorption models, which solely rely on neutral species, the inclusion of ions leads to improved spectral fits. Fit parameters comprise the column densities of abundant contributors that allow direct estimates of the ionization states. ISMabs is provided in the appropriate format to be implemented in widely used X-ray spectral fitting packages such as XSPEC, ISIS and SHERPA.
The Astrophysical Journal Supplement Series, 2005
Extensive calculations of the atomic data required for the spectral modelling of the K-shell phot... more Extensive calculations of the atomic data required for the spectral modelling of the K-shell photoabsorption of oxygen ions have been carried out in a multicode approach. The present level energies and wavelengths for the highly ionized species (electron occupancies 2 ≤ N ≤ 4) are accurate to within 0.5 eV and 0.02 Å, respectively. For N > 4, lack of measurements, wide experimental scatter, and discrepancies among theoretical values are handicaps in reliable accuracy assessments. The radiative and Auger rates are expected to be accurate to 10% and 20%, respectively, except for transitions involving strongly mixed levels. Radiative and Auger dampings have been taken into account in the calculation of photoabsorption cross sections in the K-threshold region, leading to overlapping lorentzian shaped resonances of constant widths that cause edge smearing. The behavior of the improved opacities in this region has been studied with the xstar modelling code using simple constant density slab models, and is displayed for a range of ionization parameters.
AIP Conference Proceedings
The iron L-shell ions (Fe 17+ to Fe 23+) play an important role in determining the thermal and io... more The iron L-shell ions (Fe 17+ to Fe 23+) play an important role in determining the thermal and ionization structures and line emission from photoionized plasmas. Current uncertainties in the theoretical low temperature dielectronic recombination (DR) rate coefficients for these ions significantly affect our ability to model and interpret the line emission from observations of photoionized plasmas. To help resolve this issue, we have initiated a program of laboratory measurements to produce reliable low temperature DR rates for the L-shell iron. Here we present some of our recent results and discuss some of the astrophysical implications.
Journal of Physics: Conference Series
Synopsis Dielectronic recombination rate coefficients are computed for the Si-like isoelectronic ... more Synopsis Dielectronic recombination rate coefficients are computed for the Si-like isoelectronic sequence, focusing on the near-threshold resonances of S 2+ .
AIP Conference Proceedings, 2003
AIP Conference Proceedings, 1995
We review work on the electron-impact ionization of the transition-series metals Ti3+ and Sc2+. T... more We review work on the electron-impact ionization of the transition-series metals Ti3+ and Sc2+. The early experimental and theoretical work of Falk et al. (Phys. Rev. Letts. 47 494, 1981) demonstrated that the ionization cross section for Ti3+ in the threshold region is completely dominated by the inner-shell excitation 3p63d↠3p53d2 followed by autoionization. Much later, a joint theoretical and experimental analysis by Pindzola et al. (Phys. Rev. A 49 933, 1994) confirmed that indirect processes also dominate the ionization of Sc2+. For Ti3+, comparison of recent close-coupling calculations of inner-shell excitation to the three autoionizing terms of 3p53d2 with distorted-wave calculations and experiment indicate that continuum coupling effects are relatively small, while correlation within the initial target state is important. In the case of Sc2+, for which all 19 terms of 3p53d2 are autoionizing, continuum coupling to the singly excited states 3p6nl affects the contributions from resonant excitation followed by double autoionization.
AIP Conference Proceedings, 1993
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Papers by Thomas Gorczyca