Atomic Radiative Research Articles

Survival of Terrestrial N2–O2 Atmospheres in Violent XUV Environments through Efficient Atomic Line Radiative Cooling

Atmospheres play a crucial role in planetary habitability. Around M dwarfs and young Sun-like stars, planets receiving the same insolation as the present-day Earth are exposed to intense stellar X-rays and extreme-ultraviolet (XUV) radiation. This study explores the fundamental question of whether the atmosphere of present-day Earth could survive in such harsh XUV environments. Previous theoretical studies suggest that stellar XUV irradiation is sufficiently intense to remove such atmospheres completely on short timescales. In this study, we develop a new upper-atmospheric model and re-examine the thermal and hydrodynamic responses of the thermospheric structure of an Earth-like N2–O2 atmosphere, on an Earth-mass planet, to an increase in the XUV irradiation. Our model includes the effects of radiative cooling via electronic transitions of atoms and ions, known as atomic line cooling, in addition to the processes accounted for by previous models. We demonstrate that atomic line cooling dominates over the hydrodynamic effect at XUV irradiation levels greater than several times the present level of the Earth. Consequentially, the atmosphere’s structure is kept almost hydrostatic, and its escape remains sluggish even at XUV irradiation levels up to a thousand times that of the Earth at present. Our estimates for the Jeans escape rates of N2–O2 atmospheres suggest that these 1 bar atmospheres survive in early active phases of Sun-like stars. Even around active late M dwarfs, N2–O2 atmospheres could escape significant thermal loss on timescales of gigayears. These results give new insights into the habitability of terrestrial exoplanets and the Earth’s climate history.

Experimental determination of the oxygen K-shell fluorescence yield using thin SiO2 and Al2O3 foils

In this work, the K-shell fluorescence yield for oxygen ωO,K−shell is determined experimentally, employing the radiometrically calibrated X-ray fluorescence instrumentation of the Physikalisch-Technische Bundesanstalt (PTB), Germany's National Metrology Institute. Four free-standing thin foils with two different thicknesses of both SiO2 and Al2O3 were used in order to derive an experimental value for this atomic fundamental parameter. Multiple excitation photon energies were applied to record fluorescence spectra of all four samples. The resulting value (ωO,K−shell=0.00688±0.00036) is almost 20 % higher than the commonly used value from the Krause tables [M. Krause, Atomic Radiative and Radiationless Yields for K and L shells, J. Phys. Chem. Ref. Data 8(2), 307–327 (1979)]. In addition, the achieved total uncertainty budget for the new experimental value is reduced significantly in comparison to available literature data. For validation purposes, thin SiO2 layers on Si samples were used. Here, the layer thicknesses derived from X-ray reflectometry are well in line with our X-ray fluorescence quantification results based on the new experimental value for the O K-shell fluorescence yield.

Liouville-space R-matrix-Floquet description of atomic radiative processes involving autoionizing states in the presence of intense electromagnetic fields

A reduced-density-operator description is developed for coherent optical phenomena in many-electron atomic systems, utilizing a Liouville-space, multiple-mode Floquet–Fourier representation. The Liouville-space formulation provides a natural generalization of the ordinary Hilbert-space (Hamiltonian) R-matrix-Floquet method, which has been developed for multi-photon transitions and laser-assisted electron–atom collision processes. In these applications, the R-matrix-Floquet method has been demonstrated to be capable of providing an accurate representation of the complex, multi-level structure of many-electron atomic systems in bound, continuum, and autoionizing states. The ordinary Hilbert-space (Hamiltonian) formulation of the R-matrix-Floquet method has been implemented in highly developed computer programs, which can provide a non-perturbative treatment of the interaction of a classical, multiple-mode electromagnetic field with a quantum system. This quantum system may correspond to a many-electron, bound atomic system and a single continuum electron. However, including pseudo-states in the expansion of the many-electron atomic wave function can provide a representation of multiple continuum electrons. The ‘dressed’ many-electron atomic states thereby obtained can be used in a realistic non-perturbative evaluation of the transition probabilities for an extensive class of atomic collision and radiation processes in the presence of intense electromagnetic fields. In order to incorporate environmental relaxation and decoherence phenomena, we propose to utilize the ordinary Hilbert-space (Hamiltonian) R-matrix-Floquet method as a starting-point for a Liouville-space (reduced-density-operator) formulation. To illustrate how the Liouville-space R-matrix-Floquet formulation can be implemented for coherent atomic radiative processes, we discuss applications to electromagnetically induced transparency, as well as to related pump–probe optical phenomena, and also to the unified description of radiative and dielectronic recombination in electron–ion beam interactions and high-temperature plasmas.

Testing Parity with Atomic Radiative Capture ofμ−

The next generation of "intensity frontier" facilities will bring a significant increase in the intensity of subrelativistic beams of μ(-). We show that the use of these beams in combination with thin targets of Z~30 elements opens up the possibility of testing parity-violating interactions of muons with nuclei via direct radiative capture of muons into atomic 2S orbitals. Since atomic capture preserves longitudinal muon polarization, the measurements of the gamma ray angular asymmetry in the single photon 2S(1/2)-1S(1/2) transition will offer a direct test of parity. We calculate the probability of atomic radiative capture taking into account the finite size of the nucleus to show that this process can dominate over the usual muonic atom cascade and that the as-yet unobserved single photon 2S(1/2)-1S(1/2) transition in muonic atoms can be detected in this way using current muon facilities.

Atomic Structures and Radiative Properties of He-like Ions in Debye Plasmas

A detailed investigation of plasma screening effects on atomic structure and transition properties are presented for He-like ions embedded in dense plasma environment. Multi-configuration Dirac-Fock calculations were carried out for these ions by considering a Debye-Hückel potential. A large-scale relativistic configuration-interaction method is adopted to calculate transition energies and transition probabilities and to allow for a systematic improvement of the calculations. Comparison of the presently calculated results with others, when available, is made.

Atomic Diffusion and Radiative Accelerations in Stars

Atomic diffusion can have detectable effects in many kinds of stars, each time that mixing processes are not efficient enough to prevent the build up of abundance stratifications. In this talk, after presentation of some general aspects about diffusion processes in stars, I will discuss the role of radiative acceleration which is one of the important quantities determining diffusion velocities. I will also discuss some aspects specific to stellar atmospheres, in particular for stars exhibiting strong magnetic fields.

Suppression of Atomic Radiative Collisions by Tuning the Ground State Scattering Length

We investigate the radiative collision rate in an ultracold, optically trapped cesium gas near a magnetically tunable Feshbach resonance. The radiative trap loss is suppressed by a factor of up to 15 when the node of the ground state pair correlation function is tuned to the Condon point. This constitutes a direct measurement of both the sign and the magnitude of the $s$-wave scattering length. In addition, we observe several narrow, superimposed loss resonances. Their widths are determined by the gas temperature, and their positions are independent of external parameters to within 5 mG.

Atomic Radiative Processes

Peter R Fontana 1982 New York: Academic xv + 270 pp price $32.50 ISBN 012 262 0208 The interaction of atoms with the electromagnetic fields in which they are immersed has long been a central topic of modern physics. Thus the classical work of Lorentz led naturally to the early quantum studies of Einstein, Dirac and Heitler, and this in its turn to the modern quantum field theory investigations of Janossy, Loudon, Glauber etc.

Atomic Spectra and Radiative Transitions

Atomic Spectra and Radiative Transitions

Atomic L-Shell Coster-Kronig, Auger, and Radiative Rates and Flourescence Yields for Na-Th

Calculated Auger, Coster-Kronig, super Coster-Kronig, and radiative transition rates are used to compute atomic $M$-shell Auger, Coster-Kronig, and fluorescence yields. Comparison is made with five fluorescence-field measurements, with full width at half-maximum measurements of $L\ensuremath{-}M$ x rays, and with Bhalla's relativistic radiative-yield calculations.