X-ray spectra induced by slow highly charged Arq+ ions in collision with Nb surface

The X-ray spectra of Nb surface induced by Arq+ (q = 16,17) ions with the energy range from 10 to 20 keV/q were studied by the optical spectrum technology. The experimental results indicate that the multi-electron excitation occurred as a highly charged Ar16+ ion was neutralized below the metal surface. The K shell electron of Ar16+ was excited and then de-excited cascadly to emit K X-ray. The intensity of the X-ray emitted from K shell of the hollow Ar atom decreased with the increase of projectile kinetic energy. The intensity of the X-ray emitted from L shell of the target atom Nb increased with the increase of projectile kinetic energy. The X-ray yield of Ar17+ is three magnitude orders larger than that of Ar16+.

X-ray spectra produced by interaction of Ar16+ and Ar17+ with Zr

The 10-20 qkeV Ar16+ and Ar17+ ions produced by SECRAL enter on metallic surface of Zr. In this interaction, the multi-electron excitation possibly occurred in the neutralization of the highly charged Ar16+ ions, which produced vacancy in the K shell. Electron of the high n state de-excited to K vacancy gives off X-ray. The experimental results show that X-ray intensities for the Ar hollow atom decrease with increase of incidence energy, and L beta X-ray intensities of target atom Zr increase with increasing incidence energy. K alpha X-ray yield per ion for Ar17+ was five orders of magnitude greater than that for Ar16+

X-ray spectra induced by Xe-129(q+) impacting the metal surface

Using the slow highly charged ions Xe-129(q+) (q = 25, 26, 27; initial kinetic T-0 <= 4.65 keV/a.u.) to impact Au surface, the Au atomic M alpha characteristic X-ray spectrum is induced. The result shows that as long as the charge state of projectile is high enough, the heavy atomic characteristic X-ray can be effectively excited even though the incident beam is very weak (nA magnitude), and the X-ray yield per ion is in the order of 10(-8) and increases with the kinetic energy and potential energy of projectile. By measuring the Au M alpha-X-ray spectra, Au atomic N-level lifetime is estimated at about 1.33x10(-18) s based on Heisenberg uncertainty relation.

X-ray spectra induced in highly charged Ar-40(q+) interacting with Au surface

By use of optical spectrum technology, the spectra of X-ray induced by highly charged Ar-40(q+) ions interacting with Au surface have been studied. The results show that the argon K alpha X-ray were emitted from the hollow atoms formed below the surface. There is a process of multi-electron exciting in neutralization of the Ar16+ ion, with electronic configuration 1s(2) in its ground state below the solid surface. The yield of the projectile K alpha X-ray is related to its initial electronic configuration, and the yield of the target X-ray is related to the projectile kinetic energy.

Line intensity enhancements in stellar coronal X-ray spectra due to opacity effects

Context. The I(15.01 Å)/I(16.78 Å) emission line intensity ratio in Fe xvii has been reported to deviate from its theoretical value
in solar and stellar X-ray spectra. This is attributed to opacity in the 15.01 Å line, leading to a reduction in its intensity, and was
interpreted in terms of a geometry in which the emitters and absorbers are spatially distinct.
Aims. We study the I(15.01 Å)/I(16.78 Å) intensity ratio for the active cool dwarf EV Lac, in both flare and quiescent spectra.
Methods. The observations were obtained with the Reflection Grating Spectrometer on the XMM-Newton satellite. The emission
measure distribution versus temperature reconstruction technique is used for our analysis.
Results. We find that the 15.01 Å line exhibits a significant enhancement in intensity over the optically thin value. To our knowledge,
this is the first time that such an enhancement has been detected on such a sound statistical basis. We interpret this enhancement
in terms of a geometry in which the emitters and absorbers are not spatially distinct, and where the geometry is such that resonant
pumping of the upper level has a greater effect on the observed line intensity than resonant absorption in the line-of-sight.

An investigation of Fe XVI emission lines in solar and stellar extreme-ultraviolet and soft X-ray spectra

New fully relativistic calculations of radiative rates and electron impact excitation cross-sections for Fe XVI are used to determine theoretical emission-line ratios applicable to the 251-361 and 32-77 angstrom portions of the extreme-ultraviolet (EUV) and soft X-ray spectral regions, respectively. A comparison of the EUV results with observations from the Solar Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS) reveals excellent agreement between theory and experiment. However, for emission lines in the 32-49 angstrom portion of the soft X-ray spectral region, there are large discrepancies between theory and measurement for both a solar flare spectrum obtained with the X-Ray Spectrometer/Spectrograph Telescope (XSST) and for observations of Capella from the Low- Energy Transmission Grating Spectrometer (LETGS) on the Chandra X-ray Observatory. These are probably due to blending in the solar flare and Capella data from both first-order lines and from shorter wavelength transitions detected in second and third order. By contrast, there is very good agreement between our theoretical results and the XSST and LETGS observations in the 50-77 angstrom wavelength range, contrary to previous results. In particular, there is no evidence that the Fe XVI emission from the XSST flare arises from plasma at a much higher temperature than that expected for Fe XVI in ionization equilibrium, as suggested by earlier work.

Multidimensional modelling of X-ray spectra for AGN accretion disc outflows - III. Application to a hydrodynamical simulation

We perform multidimensional radiative transfer simulations to compute spectra for a hydrodynamical simulation of a line-driven accretion disc wind from an active galactic nucleus. The synthetic spectra confirm expectations from parametrized models that a disc wind can imprint a wide variety of spectroscopic signatures including narrow absorption lines, broad emission lines and a Compton hump. The formation of these features is complex with contributions originating from many of the different structures present in the hydrodynamical simulation. In particular, spectral features are shaped both by gas in a successfully launched outflow and in complex flows where material is lifted out of the disc plane but ultimately falls back. We also confirm that the strong Fe Ka line can develop a weak, red-skewed line wing as a result of Compton scattering in the outflow. In addition, we demonstrate that X-ray radiation scattered and reprocessed in the flow has a pivotal part in both the spectrum formation and determining the ionization conditions in the wind. We find that scattered radiation is rather effective in ionizing gas which is shielded from direct irradiation from the central source. This effect likely makes the successful launching of a massive disc wind somewhat more challenging and should be considered in future wind simulations. © 2010 The Authors. Journal compilation © 2010 RAS.

Multidimensional modelling of X-ray spectra for AGN accretion disc outflows

We use a multidimensional Monte Carlo code to compute X-ray spectra for a variety of active galactic nucleus (AGN) disc-wind outflow geometries. We focus on the formation of blueshifted absorption features in the Fe K band and show that line features similar to those which have been reported in observations are often produced for lines of sight through disc-wind geometries. We also discuss the formation of other spectral features in highly ionized outflows. In particular, we show that, for sufficiently high wind densities, moderately strong Fe K emission lines can form and that electron scattering in the flow may cause these lines to develop extended red wings. We illustrate the potential relevance of such models to the interpretation of real X-ray data by comparison with observations of a well-known AGN, Mrk 766. Journal compilation © 2008 RAS.

Modelling the X-ray spectra of high-velocity outflows from quasars

High-velocity outflows from supermassive black holes have been invoked to explain the recent identification of strong absorption features in the hard X-ray spectra of several quasars. Here, Monte Carlo radiative transfer calculations are performed to synthesize X-ray spectra from models of such flows. It is found that simple, parametric biconical outflow models with plausible choices for the wind parameters predict spectra that are in good qualitative agreement with observations in the 2-10 keV band. The influence on the spectrum of both the mass-loss rate and opening angle of the flow are considered: the latter is important since photon leakage plays a significant role in establishing an ionization gradient within the flow, a useful discriminant between spherical and conical outflow for this and other applications. Particular attention is given to the bright quasar PG 1211+143 for which constraints on the outflow geometry and mass-loss rate are discussed subject to the limitations of the currently available observational data.

Synthetic X-ray spectra for simulations of the dynamics of an accretion flow irradiated by a quasar

Ultraviolet and X-ray observations show evidence of outflowing gas around many active galactic nuclei. It has been proposed that some of these outflows are driven off gas infalling towards the central supermassive black hole. We perform radiative transfer calculations to compute the gas ionization state and the emergent X-ray spectra for both two- and three-dimensional (3D) hydrodynamical simulations of this outflow-from-inflow scenario. By comparison with observations, our results can be used to test the theoretical models and guide future numerical simulations. We predict both absorption and emission features, most of which are formed in a polar funnel of relatively dense (10 -10 g cm ) outflowing gas. This outflow causes strong absorption for observer orientation angles of ?35°. Particularly in 3D, the strength of this absorption varies significantly for different lines of sight owing to the fragmentary structure of the gas flow. Although infalling material occupies a large fraction of the simulation volume, we do not find that it imprints strong absorption features in the X-ray spectra since the ionization state is predicted to be very high. Thus, an absence of observed inflow absorption features does not exclude the models. The main spectroscopic consequence of the infalling gas is a Compton-scattered continuum component that partially re-fills the absorption features caused by the outflowing polar funnel. Fluorescence and scattering in the outflow are predicted to give rise to several emission features including a multicomponent Fe Ka emission complex for all observer orientations. For the hydrodynamical simulations considered, we predict both ionization states and column densities for the outflowing gas that are too high to be quantitatively consistent with well-observed X-ray absorption systems. Nevertheless, our results are qualitatively encouraging and further exploration of the model parameter space is warranted. Higher resolution hydrodynamic simulations are needed to determine whether the outflows fragment on scales unresolved in our current study, which may yield the denser lower ionization material that could reconcile the models and the observations. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Multidimensional modelling of X-ray spectra for AGN accretion disc outflows - II

Highly ionized fast accretion disc winds have been suggested as an explanation for a variety of observed absorption and emission features in the X-ray spectra of active galactic nuclei. Simple estimates have suggested that these flows may be massive enough to carry away a significant fraction of the accretion energy and could be involved in creating the link between supermassive black holes and their host galaxies. However, testing these hypotheses, and quantifying the outflow signatures, requires high-quality theoretical spectra for comparison with observations. Here, we describe extensions of our Monte Carlo radiative transfer code that allow us to generate realistic theoretical spectra for a much wider variety of disc wind models than that was possible in our previous work. In particular, we have expanded the range of atomic physics simulated by the code so that L- and M-shell ions can now be included. We have also substantially improved our treatment of both ionization and radiative heating such that we are now able to compute spectra for outflows containing far more diverse plasma conditions. We present example calculations that illustrate the variety of spectral features predicted by parametrized outflow models and demonstrate their applicability to the interpretation of data by comparison with observations of the bright quasar PG1211+143. We find that the major features in the observed 2-10 keV spectrum of this object can be well reproduced by our spectra, confirming that it likely hosts a massive outflow. © 2010 The Authors. Journal compilation © 2010 RAS.

X-Ray spectra of superheavy and quasi-superheavy elements

We discuss the possibility of identifying superheavy elements from the observation of their M-shell x-ray spectra, which might occur during the collision of a superheavy element with a heavy target. The same question is discussed for the possible observation of the x-rays from the quasimolecule (quasi-superheavy element) which is formed during such a heavy-ion collision. It is shown that it is very difficult, if not impossible, to determine any information about the interesting quantum electrodynamical effects from the M-shell x-ray spectra of these quasimolecules.

Performance of GEANT4 in dosimetry applications: Calculation of X-ray spectra and kerma-to-dose equivalent conversion coefficients

In order to validate the Geant4 toolkit for dosimetry applications, simulations were performed to calculate conversion coefficients h(10, alpha) from air kerma free-in-air to personal dose equivalent Hp(10, a). The simulations consisted of two parts: the production of X-rays with radiation qualities of narrow and wide spectra, and the interaction of radiation with ICRU tissue-equivalent and ISO water slab phantoms. The half-value layers of the X-ray spectra obtained by simulation were compared with experimental results. Mean energy, spectral resolution, half-value layers and conversion coefficients were compared with ISO reference values. The good agreement between results from simulation and reference data shows that the Geant4 is suitable for dosimetry applications which involve photons with energies in the range of ten to a few hundreds of keV. (C) 2008 Elsevier Ltd. All rights reserved.

Optimization of x-ray spectra in digital mammography through Monte Carlo simulations

In this work, a Monte Carlo code was used to investigate the performance of different x-ray spectra in digital mammography, through a figure of merit (FOM), defined as FOM = CNR2/(D) over bar (g), with CNR being the contrast-to-noise ratio in image and (D) over bar (g) being the average glandular dose. The FOM was studied for breasts with different thicknesses t (2 cm <= t <= 8 cm) and glandular contents (25%, 50% and 75% glandularity). The anode/filter combinations evaluated were those traditionally employed in mammography (Mo/Mo, Mo/Rh, Rh/Rh), and a W anode combined with Al or K-edge filters (Zr, Mo, Rh, Pd, Ag, Cd, Sn), for tube potentials between 22 and 34 kVp. Results show that the W anode combined with K-edge filters provides higher values of FOM for all breast thicknesses investigated. Nevertheless, the most suitable filter and tube potential depend on the breast thickness, and for t >= 6 cm, they also depend on breast glandularity. Particularly for thick and dense breasts, a W anode combined with K-edge filters can greatly improve the digital technique, with the values of FOM up to 200% greater than that obtained with the anode/filter combinations and tube potentials traditionally employed in mammography. For breasts with t < 4 cm, a general good performance was obtained with the W anode combined with 60 mu m of the Mo filter at 24-25 kVp, while 60 mu m of the Pd filter provided a general good performance at 24-26 kVp for t = 4 cm, and at 28-30 and 29-31 kVp for t = 6 and 8 cm, respectively.