Basic Atomic Physics Research Articles

Parity violation in resonant inelastic soft x-ray scattering at entangled core holes.

Resonant inelastic x-ray scattering (RIXS) is a major method for investigation of electronic structure and dynamics, with applications ranging from basic atomic physics to materials science. In RIXS applied to inversion-symmetric systems, it has generally been accepted that strict parity selectivity applies in the sub-kilo-electron volt region. In contrast, we show that the parity selection rule is violated in the RIXS spectra of the free homonuclear diatomic O2 molecule. By analyzing the spectral dependence on scattering angle, we demonstrate that the violation is due to the phase difference in coherent scattering at the two atomic sites, in analogy with Young's double-slit experiment. The result also implies that the interpretation of x-ray absorption spectra for inversion symmetric molecules in this energy range must be revised.

Reproducible Spectrum and Hyperspectrum Data Analysis Using NeXL.

NeXL is a collection of Julia language packages (libraries) for X-ray microanalysis data processing. NeXLCore provides basic atomic and X-ray physics data and models including support for microanalysis-related data types for materials and k-ratios. NeXLMatrixCorrection provides algorithms for matrix correction and iteration. NeXLSpectrum provides utilities and tools for energy-dispersive X-ray spectrum and hyperspectrum analysis including display, manipulation, and fitting. NeXL is integrated with the Julia language infrastructure. NeXL builds on the Gadfly plotting library and the DataFrames tabular data library. When combined with the DrWatson package, NeXL can provide a highly reproducible environment in which to process microanalysis data. Data availability and reproducible data analysis are two keys to scientific reproducibility. Not only should readers of journal articles have access to the data, they should also be able to reproduce the analysis steps that take the data to final results. This paper will both discuss the NeXL framework and provide examples of how it can used for reproducible data analysis.

APAPES - Atomic Physics with Accelerators: Projectile Electron Spectroscopy

The only existing heavy-ion accelerator in Greece, the 5.5 MV TANDEM at the National Research Center “Demokritos” in Athens has been used to date primarily for investigations centering around nuclear physics. Here, we propose to establish the new (for Greece) discipline of Atomic Physics with Accelerators, a strong field in the EU with important contributions to fusion, hot plasmas, astrophysics, accelerator technology and basic atomic physics of ion-atom collision dynamics, structure and technology. This will be accomplished by combining the existing interdisciplinary atomic collisions expertise from three Greek universities, the strong support of distinguished foreign researchers and the high technical ion-beam know-how of the TANDEM group into a cohesive initiative.Using the technique of Zero-degree Auger Projectile Spectroscopy (ZAPS), we shall complete a much needed systematic isoelectronic investigation of K-Auger spectra emitted from collisions of pre-excited ions with gas targets using novel techniques. Our results are expected to lead to a deeper understanding of the neglected importance of cascade feeding of metastable states [1] in collisions of ions with gas targets and further elucidate their role in the non-statistical production of excited three-electron states by electron capture, recently a field of conflicting interpretations awaiting further resolution.

Atomic Physics at the 5 MV Tandem at Demokritos: the UoC APAPES project

University of Crete (UoC) has initiated the research initiative APAPES funded by THALES‡ that has already set up a new experimental station with a beam line dedicated solely on basic atomic physics research. This new experiment utilizing Zero-degree Auger Projectile Spectroscopy (ΖΑPS) is located at the 5 MV TANDEM accelerator of the National Center for Scientific Research (NCSR) “Demokritos” in Athens, and has been put together to perform high resolution studies of electrons emitted during ion-atom collisions. The apparatus consists of a Hemispherical Deflector Analyzer (HDA) combined with a 2-dimensional Position Sensitive Detector (PSD) and a doubly-differentially pumped gas cell containing the gas-target. The goal is to perform a systematic isoelectronic investigation of K-Auger spectra emitted from pre-excited and ground state He-like ions in collisions with gas targets using novel techniques. So far, various Auger electron spectra produced through collisions of mixed state (1s2, 1s2s3S) C4+ ion beam with various gas targets have been recorded. In addition, detailed simulations using SIMION have also explored the optimal lens voltages and the solid angle correction factors for long-lived metastable states. A terminal gas stripper system is scheduled to be installed in the accelerator, extending its range of available charge states and enabling the production of pure ground state as well as mixed state beams with different metastable fractions, a measurement vital to APAPES. Here, we report on the progress made up to date on the APAPES project, the description of the apparatus, updated results and plans for the near future.

Ac Stark shift measurements of the clock transition in cold Cs atoms: Scalar and tensor light shifts of theD2transition

The ac Stark shift, or light shift, is a physical phenomenon that plays a fundamental role in many applications ranging from basic atomic physics to applied quantum electronics. Here, we discuss experiments testing light-shift theory in a cold-atom cesium fountain clock for the Cs ${D}_{2}$ transition (i.e., $6\phantom{\rule{0.28em}{0ex}}{}^{2}{S}_{1/2}\ensuremath{\rightarrow}6\phantom{\rule{0.28em}{0ex}}{}^{2}{P}_{3/2}$ at 852 nm). Cold-atom fountains represent a nearly ideal system for the study of light shifts: (1) The atoms can be perturbed by a field of arbitrary character (e.g., coherent field or nonclassical field); (2) there are no trapping fields to complicate data interpretation; (3) the probed atoms are essentially motionless in their center-of-mass reference frame, $T$ \ensuremath{\sim} 1 \ensuremath{\mu}K; and (4) the atoms are in an essentially collisionless environment. Moreover, in the present work the resolution of the Cs excited-state hyperfine splittings implies that the ${D}_{2}$ ac Stark shift contains a nonzero tensor polarizability contribution, which does not appear in vapor phase experiments due to Doppler broadening. Here, we test the linearity of the ac Stark shift with field intensity, and measure the light shift as a function of field frequency, generating a ``light-shift curve.'' We have improved on the previous best test of theory by a factor of 2, and after subtracting the theoretical scalar light shift from the experimental light-shift curves, we have isolated and tested the tensor light shift for an alkali ${D}_{2}$ transition.

The geocoronal H α cascade component determined from geocoronal H β intensity measurements

AbstractGeocoronal H α and H β intensity measurements using the Wisconsin H α Mapper Fabry‐Perot are used to determine the intensity of the H α cascade component. From basic atomic physics and the work of Meier (), we show that the total cascade in geocoronal H α emission is 0.52 ± 0.03 times the geocoronal H β intensity, I(H β), for solar Lyman series excitation of geocoronal hydrogen. The results are consistent with the H α cascade measurements of Mierkiewicz et al. (), which were determined directly from the analysis of H α line profile measurements, and significantly narrow the range of uncertainty in the cascade measurement. Accounting for cascade is essential in determining exospheric effective temperatures and dynamics from the shape of the geocoronal H α line.

New effective recombination coefficients for nebular N ii lines(Corrigendum)

Errors in the computed effective recombination coefficients for nebular N ii lines in an earlier publication (Fang et al. 2011) have been discovered and are here corrected. Those errors were not due to the basic atomic physics (i.e. creation of the N2+ target and the target wave functions, and calculations of bound-state energies, oscillator strengths and photoionization cross-sections for the N ii states) but due to mislabeling of five N ii bound-state energy levels. The 2p3p P1 level was originally labeled as 2p3p S1, the 2p3p S1 level was labeled as 2p3p P1, and the 2p3p P1 level was labeled as 2p3p P1; labels of the 2p3d D2 and 2p3d D2 levels were swapped. As a consequence, the effective recombination coefficients for the N ii lines that are directly related to the above five states were incorrect. We have corrected the labeling of the N ii energy levels and re-calculated the effective recombination coefficients for the N ii lines at the same electron temperature and density ranges as in Fang et al. (2011). The newly calculated effective recombination coefficients are given in Tables 3–6.

Effect of optical pumping in saturated absorption spectroscopy: an analytic study for two-level atoms

We present the analytic solutions of the saturated absorption spectrum for an atomic medium composed of two-level atoms and describe the effects of saturation and optical pumping on the spectrum. The background-subtracted Doppler-free spectrum is Lorentzian-shaped with an amplitude and width given by 1 − {1 + s0[1 + (γ2t/2)]}−1/2 and γt[1 + {1 + s0[1 + (γ2t/2)]}1/2], respectively, where γt is the transverse decay rate, γ2 is the decay rate to energy levels other than the ground state, s0 is the saturation parameter and t is the interaction time of the atoms with laser beams. Analytic results are compared with numerical results and show good agreement with one another. This paper is intended for graduate students who have started to study basic atomic physics.

Spectroscopy with trapped highly charged ions

We give an overview of atomic spectroscopy performed on electron beam ion traps at various locations throughout the world. Spectroscopy at these facilities contributes to various areas of science and engineering, including but not limited to basic atomic physics, astrophysics, extreme ultraviolet lithography, and the development of density and temperature diagnostics of fusion plasmas. These contributions are accomplished by generating, for example, spectral surveys, making precise radiative lifetime measurements, accounting for radiative power emitted in a given wavelength band, illucidating isotopic effects, and testing collisional–radiative models. While spectroscopy with electron beam ion traps had originally focused on the x-ray emission from highly charged ions interacting with the electron beam, the operating modes of such devices have expanded to study radiation in almost all wavelength bands from the visible to the hard x-ray region; and at several facilities the ions can be studied even in the absence of an electron beam. Photon emission after charge exchange or laser excitation has been observed; and the work is no longer restricted to highly charged ions. Much of the experimental capabilities are unique to electron beam ion traps, and the work performed with these devices cannot be undertaken elsewhere. However, in other areas the work on electron beam ion traps rivals the spectroscopy performed with conventional ion traps or heavy-ion storage rings. The examples we present highlight many of the capabilities of the existing electron beam ion traps and their contributions to physics.

Highly Charged Ion Research at the Livermore Electron Beam Ion Traps

Spectroscopy performed with the three Livermore electron beam ion traps is reviewed, which is continuing and complementing the innumerable contributions to atomic physics provided over the years by heavy-ion accelerators. Numerous spectrometers were developed that cover the spectral bands from the visible to the hard x-ray region. These enabled exhaustive line surveys useful for x-ray astrophysics and for systematic studies along iso-electronic sequences, such as the 4s–4p, 3s–3p, and 2s–2p transitions in ions of the Cu-I, Na-I, and Li-I sequences useful for studying QED and correlation effects as well as for precise determinations of atomic-nuclear interactions. They also enabled measurements of radiative transition probabilities of very long-lived (milli- and microseconds) and very short-live (femtosecond) levels. Because line excitation processes can be controlled by choice of the electron beam energy, the observed line intensities are used to infer cross sections for electron-impact excitation, dielectronic recombination, resonance excitation, and innershell ionization. These capabilities have recently been expanded to simulate x-ray emission from comets by charge exchange. Specific contributions to basic atomic physics, nuclear physics, and high-temperature diagnostics are illustrated.

X-ray spectral diagnostics of neon photoionization experiments on the Z-machine

We report on an initial spectroscopic study of low-density, x-ray photoionized neon with x-ray spectroscopy. These experiments, carried out on the Z-machine at Sandia, are optimized to produce a gradient-free, collisionless plasma, and to explore issues related to the rapid x-ray photoionization of relatively cold, low-density plasmas. The initial experiments used time-integrated absorption spectroscopy, backlit by the pinch radiation, to determine the ionization balance in the gas cell. Future experiments will use time-resolved spectroscopy in both absorption and emission. The emission spectra are expected to be similar to those seen from photoionized astrophysical sources, such as x-ray binaries. Indeed, in addition to addressing basic plasma and atomic physics issues, these experiments are designed to help the astrophysical community better understand the new, high-resolution spectra being produced by the Chandra and XMM-Newton telescopes, and to benchmark spectral synthesis codes.

Probing the Dark Secrets of PNe with ORLs

There are two long-standing problems in nebular astrophysics: a) The dichotomy of abundance determinations whereby heavy element abundances relative to hydrogen from collisionally excited lines (CELs) are systematically lower than those from (much fainter) optical recombination lines (ORLs), a discrepancy that can be traced back to Wyse (1942) and Aller & Menzel (1945) who pioneered the ORL method; and b) The dichotomy of temperature determinations whereby Te derived from the collisionally excited [O III] forbidden line ratio is systematically higher than that derived from Balmer jump of the H I recombination spectrum, a discrepancy first discovered by Peimbert (1971) and attributed to temperature fluctuations in the nebula (Peimbert 1967). Thanks to the rapid progress in detector technology and recombination theory for multi-electron systems, significant progress has been made in recent years in our understanding of these two fundamental problems, which could potentially affect the derivation of abundances for a wide range of photoionized nebulae, both galactic and extragalactic. Both types of dichotomy are found to be real and are most likely caused by astrophysical effects rather than uncertainties in observations or in the basic atomic physics. The two problems are shown to be related and can be explained by assuming that PNe contain a small mass of extremely cold (Te ~ 103 K) inclusions, highly enriched in helium and heavy elements, embedded in diffuse material of “normal” abundances (~ solar) and temperature (Te ~ 104 K). The existence and nature of such H-deficient inclusions in PNe remains a mystery. A recent review on this subject is given by Liu (2002).

Atomic Structure Studies Using Fusion Plasmas

Atomic spectroscopy plays an important role in fusion research and extensive knowledge of atomic parameters is needed for plasma diagnostics. However, a magnetically confined hot plasma can be considered as a spectroscopic light source which has some unique properties, including high temperature and low density. Fusion devices can therefore be used to tackle problems in basic atomic physics. This paper reviews the contributions to the structure of atomic ions, which have been obtained by the spectroscopy of fusion plasmas. Studies of highly charged ions, forbidden transitions, QED effects and connections between solar physics and fusion plasma physics will be discussed.

Ugo Fano

With the passing of Ugo Fano on 13 February 2001, the Radiation Research Society lost an influential founding member. A broader community dearly misses a great theoretical physicist. Ugo Fano was born a son of Rosa Cassin and Gino Fano (1871-1952), professor of mathematics at Turin, Italy, specializing in differential geometry. Having studied mathematics first at the University of Turin, the younger Fano turned to physics under the influence of his cousin, Giulio Racah (1909-1965), a physicist known for the powerful theory of angular momentum. Then Fano was fortunate to receive postdoctoral training from two giants in modern physics: Enrico Fermi at Rome in 1934-1936 and Werner Heisenberg at Leipzig in 1936-1937. Fano's American career began with pioneering work in 1940-1944 in what was later to be called radiation biology with M. Demerec and others at the Department of Genetics of the Carnegie Institution at Cold Spring Harbor. It is noteworthy that, after a seminar in Rome by P. Jordan on the effects of X rays on genetic material, Fermi had suggested to Fano that the biological action of radiation would be an important and suitable topic for study. Fano's papers in this period concerned chromosomal rearrangements, mutations, lethal effects,more » and genetic effects of X rays and neutrons on Drosophila melanogaster, as well as theoretical analysis of genetic data. His work also included the discovery of bacteriophage-resistant mutants in Escherichia coli, following up earlier studies by Salvador E. Luria. After a wartime effort at the U.S. Army Ballistic Research Laboratory in 1944-1945, Fano joined the staff of the National Bureau of Standards in 1946. Fano's two decades at NBS saw prolific and outstanding contributions to two major areas of research: radiation physics and the basic physics of atoms, molecules and condensed matter. Many of Fano's contributions to radiation physics are seminal to later developments. In 1946, he put forth the first general theory of the yield of ionization in a gas. In 1947, he pointed out the statistical fluctuations of ionization and characterized them by what is now known as the Fano factor. In 1951-1959, he led L. V. Spencer, M. J. Berger and others in developing methods for treating the transport of photons and charged particles in matter. The invention in 1953-1954 of the degradation spectrum for characterizing electrons and other charged particles in matter was especially influential. In 1954, Fano also demonstrated the cavity principle of radiation equilibrium under general conditions. In later years at Chicago, he maintained a keen interest in radiation physics and studied topics such as the behavior of slow electrons in condensed matter, which are produced abundantly by any ionizing radiation. Fano's work after the mid-1950s focused increasingly on basic and microscopic aspects of radiation interactions with matter, including condensed-phase effects on radiation absorption (studied in 1956-1960) and stopping powers of materials (comprehensively reviewed in 1963). He continued for many years to campaign for the use of synchrotron radiation, for which numerous facilities have now been developed worldwide. The numerous, wide-ranging influences of Fano in basic physics and chemistry grew mostly from his years since 1966 at the University of Chicago. Not only did he train approximately 30 Ph.D. students and many postdoctoral fellows, but he communicated regularly with scientists around the world in meetings or by telephone calls, letters and electronic mail, liberally sharing his ideas and incisive insights into scientific matters. This style of 'doing physics' (in Fano's frequently used words) stems from Fermi, who strove to see the essence of knowledge in experimental facts and to tell it to others in simple and unpretentious words. We shall continue to learn much from his five monographs and over 250 papers.« less

Spectroscopic Features in the EUV Emission of a M8 Flare Observed by SUMER

A flare of size M8 occurred while SUMER was recording a spectral scan above the active region NOAA 8537 at the west limb. We recorded spectra during the pre-flare phase, at flare onset, and during the decay phase of this main flare in a series of events. More than 60 flare lines were identified during this observation, which include Fe XVIII - Fe XXIII lines that provide evidence of 107 K plasmas. We also recorded lines from He-like ions, such as Ne IX, Na x, Mg XI, and Si XIII. Accurate wavelength measurements of such lines are of interest in basic atomic physics studies. Using plasma diagnostic techniques, we investigated the temporal evolution of the electron densities and temperatures during the event.

Content Analysis of Taiwanese 14 year olds’ Information Processing Operations shown in Cognitive Structures Following Physics Instruction, with Relations to Science Attainment and Scientific Epistemological Beliefs

This study examined 48 Taiwanese 14 year olds' cognitive structures derived from the instruction of basic atomic physics. Content analyses of these students' information processing operations displayed in cognitive structures revealed that even academically above‐average students, in general, used relatively lower‐level modes of knowledge construction, focusing on reciting or describing specific factual knowledge in physics. Students spent more retrieval time when phrasing an idea in a higher‐order cognitive operation, such as in the mode of generalization or conditional inference. Moreover, higher achievers tended to have a richer store of knowledge frameworks, as well as to employ a more inclusive way and a variety of cognitive reasoning manners in structuring their ideas. Students holding scientific epistemological beliefs more orientated to constructivist views of science tended to use more conditional inferential reasoning than those having empiricist‐aligned views of science.

Energy systematics of the KαLi satellite transitions

The presence of X-ray satellites is common in X-ray spectra. The last compilation of satellite lines, frequently cited in the open literature, is the X-ray energy collection of Cauchois and Senemaud, Wavelengths of X-ray Emission Lines and Absorption Edges, Pergamon, Oxford, 1978 [1], which is restricted to electron and photon excitations. In the last decades, many ion-induced satellite measurements have been performed, the range covered in Ref. [1] have been extended for ∼40<Z<92, spectator vacancy number from 2 to 7, and energy-shifts from ∼200 to 1200 eV. In analytical work and in basic atomic physics research one needs the best data available on the satellite lines. We are working on a new and comprehensive compilation of experimental values for the K-satellite, and K-hypersatellite energy shifts. Some problems encountered during this work are discussed. A new semi-empirical formula for the description of the KαLi satellite energy shifts is given.

On the polarization of Hα scattered by neutral hydrogen in active galactic nuclei

Raman scattering by atomic hydrogen converts the UV continuum around Ly$\beta$ into optical continuum around H$\alpha$, and the basic atomic physics has been discussed in several works on symbiotic stars. We propose that the same process may operate in active galactic nuclei (AGN) and calculate the linear polarization of the broad emission lines Raman-scattered by a high column neutral hydrogen compnent. The conversion efficiency of the Raman scattering process is discussed and the expected scattered flux is computed using the spectral energy distribution of an AGN given by a typical power law. The high column H {\sc i} component in AGN is suggested by many observations encompassing radio through UV and X-ray ranges. When the neutral hydrogen component with a column density $\sim 10^{22} cm^{-2}$ is present around the active nucleus, it is found that the scattered H$\alpha$ is characterized by a very broad width $\sim 20,000 km/s$ and that the strength of the polarized flux is comparable to that of the electron-scattered flux expected from a conventional unified model of narrow line AGN. The width of the scattered flux is mainly determined by the column density of the neutral scatterers where the total scattering optical depth becomes of order unity. The asymmetry in the Raman scattering cross section around Ly$\beta$ introduces red asymmetric polarized profiles around H$\alpha$. The effects of the blended Ly$\beta$ and O {\sc vi} 1034 doublet are also investigated. We briefly discuss the spectropolarimetric observations performed on the Seyfert galaxy IRAS 110548-1131 and the narrow line radio galaxy Cyg A.

A comparison of the -emission properties of pasty, liquid and glassy -eucryptite ion sources

The emission properties of the -eucryptite compound in the pasty, liquid and glassy forms were investigated. It was found that the liquid -eucryptite emits ten times more lithium than does its pasty counterpart whereas the glassy one not only keeps this high emission property but is also a very convenient ion source due to its being much easier to handle, making it a valuable candidate for a -ion source for low-energy fast neutral lithium beam diagnostics (<10 keV). Our results suggest that it should be possible to measure the plasma-density fluctuations besides the densities with such diagnostics. The lifetime of the lithium emitter in high-current-extraction mode is much increased when glassy sources are used. Furthermore, using the same transformation method for all other aluminosilicates used for extraction of alkali-metal and thallium ions may improve their output, making new possibilities available in the area of basic atomic physics and in the field of heavy-ion-beam probe plasma diagnostics.

Equilibrium Ionization and Non-Equilibrium Ionization Plasma Models

AbstractThis paper provides a brief review on ionization and radiation models of an optically thin, hot plasma and their application to the interpretation of observations of the Local Bubble. The basic structure and atomic physics ingredients of the models are outlined. Some general characteristic results of ionization equilibrium and non-equilibrium calculations are shown. Recent progress in plasma model codes is reviewed. The interpretation of the observations of absorption lines and emission spectra from the Local Bubble is discussed in the framework of ionization equilibrium and non-equilibrium ionization models with particular reference to the fast adiabatic cooling model of Breitschwerdt and Schmutzler.