Steven T. Manson

Bio: Steven T. Manson is an academic researcher from Georgia State University. The author has contributed to research in topics: Photoionization & Ionization. The author has an hindex of 36, co-authored 302 publications receiving 6173 citations. Previous affiliations of Steven T. Manson include Indian Institutes of Technology & National Institute of Standards and Technology.

Photo-Ionization in the Soft x-Ray Range: 1 Z Dependence in a Central-Potential Model

Abstract: Using a one-electron model with a Herman-Skillman central potential, photo-ionization calculations have been performed which emphasize the soft x-ray spectral range (\ensuremath{\sim}100 eV to \ensuremath{\sim}2 keV). The ${M}_{\mathrm{II},\mathrm{III}}(3p)$ subshell was studied in Ar, Cu, and Ge, as well as the ${M}_{\mathrm{IV},\mathrm{V}}(3d)$ and ${M}_{\mathrm{II},\mathrm{III}}$ in Kr, Rh, Xe, Eu, Au, and Fm in an effort to explain the combined $Z$ and energy dependence of the photo-ionization cross sections for these subshells. In addition, calculations have been performed for $3s$, $4s$, $5s$, $4p$, $5p$, $4d$, $5d$, and $4f$ subshells in certain elements. The results, which are considerably different from the predictions of the hydrogenlike model, show certain regularities which are explained in terms of the potentials. Comparisons with experiment show that the model correctly predicts the gross spectral shape of photo-ionization cross sections, but the results are somewhat inaccurate in the vicinity of large absorption peaks. This calculation is considered to be a first approximation which can be improved by taking exchange into account more exactly and by including electron-electron correlation.

The early Universe

Abstract: In the past few years one of the most exciting areas of research in physics has been the interdisciplinary field of cosmology and particle physics. The NSF's Institute for Theoretical Physics in Santa Barbara devoted a 6-month program and an intensive 1-week workshop to the subject. A brief review is given of both the workshop and this field which is attracting attention, in part, because the early Universe seems to be the only laboratory in which to study grand unification.

CLOUDY 90: Numerical Simulation of Plasmas and Their Spectra

Abstract: CLOUDY is a large‐scale spectral synthesis code designed to simulate fully physical conditions within an astronomical plasma and then predict the emitted spectrum. Here we describe version 90 (C90) of the code, paying particular attention to changes in the atomic database and numerical methods that have affected predictions since the last publicly available version, C84. The computational methods and uncertainties are outlined together with the direction future development will take. The code is freely available and is widely used in the analysis and interpretation of emission‐line spectra. Web access to the Fortran source for CLOUDY, its documentation Hazy, and an independent electronic form of the atomic database is also described.

Empirical atomic sensitivity factors for quantitative analysis by electron spectroscopy for chemical analysis

Abstract: Quantitative information from electron spectroscopy for chemical analysis requires the use of suitable atomic sensitivity factors. An empirical set has been developed, based upon data from 135 compounds of 62 elements. Data upon which the factors are based are intensity ratios of spectral lines with F1s as a primary standard, value unity, and K2p3/2 as a secondary standard. The data were obtained on two instruments, the Physical Electronics 550 and the Varian IEE-15, two instruments that use electron retardation for scanning, with constant pass energy. The agreement in data from the two instruments on the same compounds is good. How closely the data can apply to instruments with input lens systems is not known. Calculated cross-section data plotted against binding energy on a log-log plot provide curves composed of simple linear segments for the strong lines: 1s, 2p3/2, 3d5/2 and 4f7/2. Similarly, the plots for the secondary lines, 2s, 3p3/2, 4d5/2 and 5d5/2, are shown to be composed of linear segments. Theoretical sensitivity factors relative to F1s should fall on similar curves, with minor correction for the combined energy dependence of instrumental transmission and mean free path. Experimental intensity ratios relative to F1s were plotted similarly, and best fit curves were calculated using the shapes of the theoretical curves as a guide. The intercepts of these best fit curves with appropriate binding energies provide sensitivity factors for the strong lines and the secondary lines for all of the elements except the rare earths and the first series of transition metals. For these elements the sensitivity factors are lower than expected, and variable, because of multi-electron processes that vary with chemical state. From the data it can be shown that many of the commonly-accepted calculated cross-section data must be significantly in error—as much as 40% in some cases for the strong lines, and far more than that for some of the secondary lines.

PENELOPE-2006: A Code System for Monte Carlo Simulation of Electron and Photon Transport

Abstract: The computer code system PENELOPE (version 2008) performs Monte Carlo simulation of coupled electron-photon transport in arbitrary materials for a wide energy range, from a few hundred eV to about 1 GeV. Photon transport is simulated by means of the standard, detailed simulation scheme. Electron and positron histories are generated on the basis of a mixed procedure, which combines detailed simulation of hard events with condensed simulation of soft interactions. A geometry package called PENGEOM permits the generation of random electron-photon showers in material systems consisting of homogeneous bodies limited by quadric surfaces, i.e., planes, spheres, cylinders, etc. This report is intended not only to serve as a manual of the PENELOPE code system, but also to provide the user with the necessary information to understand the details of the Monte Carlo algorithm.