Soft X-rays

We review recent studies using resonant inelastic X-ray scattering (RIXS) or also here denoted X-ray emission spectroscopy (XES) on liquid water and the assignment of the two sharp peaks in the lone-pair region. Using the excitation energy dependence we connect the two peaks to specific features in the X-ray absorption (XAS) spectrum which have independently been assigned to molecules in tetrahedral or distorted configurations. The polarization dependence shows that both peaks are of 1b1 origin supporting an interpretation in terms of two structural species, tetrahedral or disordered, which is furthermore consistent with the temperature-dependence of the two peaks. We discuss effects of life-time vibrational interference and how this affects the two components differently and also leads to differences in the relative peak heights for H2O and D2O. We show furthermore that the inherent structure in molecular dynamics simulations contain the structural bimodality suggested by XES, but this is smeared out in the real structure when temperature is included. We present a discussion around alternative interpretations suggesting that the origin of the two peaks is related to ultrafast dissociation and show evidence that such a model is inconsistent with several experimental observations and theoretical concepts. We conclude that the peaks reflect a temperature-dependent balance in fluctuations between tetrahedral and disordered structures in the liquid. This is well-aligned with theories of water under supercooled conditions and higher pressures where water might exist as high- or low-density liquid with different possibilities for a transition between them. With the present work we provide a link between established models for supercooled water, where water's anomalies become extreme, and ambient water, where the anomalous contributions are weaker but still important.

The responses of three types of thermoluminescence dosimeters (TLDs), namely the TLD-100, TLD-200 and Ge-doped optical fiber to soft X-ray with photon energy of 8.05 keY were measured. The X-ray source used is the vacuum spark plasma which is capable of producing intense copper K" line radiation at energy of 8.05 keY. The output dosage of the vacuum spark X-ray source is measured by a calibrated ion chamber and it is found to increase with operating voltage. The TL sensitivities of TLD-l 00, TLD-200 and Ge-doped optical fiber are determined and results are normalized to their responses to 60CO gamma rays. The TL sensitivities are found to be 1.2 for TLD-100, 29.0 for TLD-200 and 13.8 for Ge-doped Optical Fiber.

I have been assigned to get vital information out to the world and so I pray that my work is pleased by God and only God, but the good news has to be shared with my country and it seems to me that things are getting worse in 2016, in my country and I am so proud of the great United States, but so sad that people are not taking better care of their own health and believe anything the media shows them, believes what man tells you about your own body, etc.
So, let’s begin to reverse our country’s sickness and live for living for our children in the United States and have faith in God’s healing food, and let’s begin to use our common sense which God gave to each and everyone of us to use not only for ourselves, but to help and share with others.  I truly do believe this is where and when we get our blessings of the world!

A large-volume non-conventional XeCl excimer laser (Hercules) emitting long pulses (from 10 ns up to 120 ns at a wavelength of 308 nm) has been used to drive a soft X-ray plasma source. The X-rays pulse duration and the energy conversion efficiency in different spectral regions have been measured; X-rays emission lasting up to 100 ns has been obtained in the 70 eV region. The dependence of X-ray pulse duration on the size of the laser spot is  discussed. The X-ray source can be operated both in vacuum and in helium at atmospheric pressure. This allows irradiating over a large area both for contact microscopy of living specimens (up to 1 mm^2 windows) and for radiobiology (up to few cm^2 windows). The experimental results obtained for these two applications as well as for radiographic images of living insects are discussed.

An extremely high resolution flat field type slit less soft x-ray emission spectrometer has been designed and constructed for the long undulator beamline BL07LSU in SPring-8. By optimizing the ruling parameters of two cylindrical gratings, a high energy resolution ΔE < 100 meV and/or an E/ΔE ∼ 10 000 are expected for the energy range of 350 eV – 750 eV taking into account the broadening by the spatial resolution (25 μm) of a CCD detector. A coma-free operation mode proposed by Strocov et al., is also applied to eliminate both defocus and coma aberrations. The spectrometer demonstrated experimentally that E/ΔE = 10 050 and 8046 for N 1s (402.1 eV) and Mn 2p (641.8 eV) edges, respectively.

The polarization dependence of the split two peaks in the lone-pair region in the x-ray emission spectra has been determined at several different excitation energies for both D2O and H2O water. In contrast to predictions based on a narrow range of local water structures where the two peaks would be of different molecular orbital symmetry and arise from, respectively, intact and dissociated molecules, we show that the two peaks in the lone-pair region are both of lone-pair 1b1 orbital symmetry. The results support the interpretation that the two peaks appear due to fluctuations between two distinct different main structural environments.

O 1s X-ray emission and X-ray absorption spectroscopy is applied to probe hydrogen bonding of water (D2O) in 3-methylpyridine. Owing to element selectivity of X-ray spectroscopies the electronic structure of water in the binary mixture was observed selectively. Based on the observed spectral changes associated with hydrogen bonding in O 1s X-ray emission and X-ray absorption spectra, we have investigated the hydrogen bond of the mixture sample over a wide range of D2O concentrations (XD2O = 0.02–1.0) at room temperature under atmospheric pressure.

We evaluate proposed interpretations of previous X-ray emission spectroscopy (XES) data on liquid water. The split peak in the lone-pair orbital region has been interpreted in terms of either two different structural motifs, tetrahedral and distorted, or as due to core-hole-induced dissociative dynamics; here we add new data on a 1:1 H2O/D2O isotopic mixture and additional spectrum simulations including the core-hole-induced dynamics. The XES spectrum of HDO is quite nicely reproduced as the sum of spectra of H2O and D2O, which we interpret as that core-hole-induced dynamics contribute only to the peak shape and do not affect the intensity ratio between tetrahedrally coordinated and distorted. We find the simulation-based interpretation of the two lone-pair peaks as being of completely different symmetries, molecular 1b1 and dissociated 3a1, difficult to reconcile with the experimental intensities in the 1b2 and 3a1 spectral regions. We report extensive theoretical simulations of spectra probing both the distance and velocity quantum distributions of the internal OH stretch; sharp features not associated with the lone-pair, that are seen when the OH stretch is treated as a classical oscillator, become smeared out when the zero-point Franck–Condon profile and momentum distribution in the v = 0 level of the OH stretch are taken into account. This demonstrates that neglecting zero-point motion in simulating XES spectra of water generates artificially sharp structures. XES spectra of 1 M and 4 M hydrochloric acid (HCl) and sodium hydroxide (NaOH) are reported. These spectra indicate that dissociated species most likely can be excluded as the origin of the double 1b1 peak structure. We thus argue that the experimental observation of two distinct peaks in the lone-pair region is less likely to be explained by an unstructured continuum model of the liquid, but is easily explained within a two-component fluctuating model.

We have measured X-ray absorption spectra for acetic acid molecules in an organic solvent in order to study the effect of hydrogen-bonding formation. The spectral shapes distorted by saturation effect were compensated by using a new correction procedure for X-ray absorption based on the changes in the concentration of the samples. A resonance peak shift was observed when the acetic acid molecules formed a cyclic dimer in hexane solution, which is similar to the behavior of cluster molecules in vacuum. This is the first report on the XAS spectral changes due to cyclic dimer formation in a solution.

The electronic structure of a material is important in many fields of science, because valence electrons play important roles in the properties of many systems including molecules in liquids and solutions. Recent studies have applied direct methods to observe the electronic state of solutions. For example, unoccupied valence states were observed for glycine using X-ray absorption spectroscopy (XAS). 1 Core-level observations of occupied valence states were reported using photoemission spectroscopy with a liquid jet technique. 2 X-Ray ...

The medicinal plants are a source of biologically important elements which are necessary both for animals and plants. Present study investigates the concentration of elemental constituents of seven selected medicinally important plants of Bangladesh, namely Terminalia bellirica, Centella asiatica, Pleurotus ostreatus, Curcuma longa, Bombax ceiba and Trigonella foenum-graecum. Appropriately desiccated samples (pellets) of these medicinal plants were bombarded with accelerated proton beam with the help of 3 MV Van de Graff accelerator at accelerator Facilities Division, Atomic Energy Center, Dhaka. Eleven different elements-P, S, K, Ca, Sc, Ti, V, Mn, Fe, Cd and I were detected by collecting the harvested X-rays with [Si(Li)] detector. Data collection and analysis were performed using Maestro-32 and GUPIX software.

A new type of collector optics was developed for grazing incident x-ray emission spectrometer. The collector optics used two cylindrical mirrors to add two extra light paths while keeping the center light path that directly illuminates the grating. The design and properties of the spectrometer using the triple-path collector optics were evaluated using ray-tracing simulations, and validity of this design in terms of throughput and energy resolution was confirmed by the experimentally obtained spectra.

Impressive images from the Hubble Space Telescope not only help scientists understand our universe, but also enhance public interest in science, becoming a gateway for the youngest generation to enter Science, Technology, Engineering, and Mathematics (STEM) fields. Heliophysics observatories can also provide dramatic images of our space environment. The Solar and Heliospheric Observatory (SOHO; Domingo et al., 1995) images the dynamic activities of our Sun and its solar corona. Solar Terrestrial Relation Observatory (STEREO; Kaiser et al., 2008) monitors solar wind features propagating through interplanetary space. Imager for Magnetopause-to-Aurora Global Exploration (IMAGE; Burch, 2000) and Two Wide-Angle Imaging Neutral-Atom Spectrometers (TWINS; Goldstein & McComas, 2018) display the activities of the Earth's inner-magnetosphere in response to varying solar wind conditions. Time History of Events and Macroscale Interactions during Substorms (THEMIS) All Sky Imagers (ASI) distributed over the northern portions of North America (Mende et al., 2008) image aurora precipitation resulting from magnetospheric activities. The one missing image is the dayside magnetosphere, the starting point for the solar wind-magnetosphere interaction.

Soft X-ray imagers can be used to study the mesoscale and macroscale density structures that occur whenever and wherever the solar wind encounters neutral atoms at comets, the Moon, and both magnetized and unmagnetized planets. Charge exchange between high charge state solar wind ions and exospheric neutrals results in the isotropic emission of soft X-ray photons with energies from 0.1 to 2.0 keV. At Earth, this process occurs primarily within the magnetosheath and cusps. Through providing a global view, wide field-of-view imaging can determine the significance of the various proposed solar wind-magnetosphere interaction mechanisms by evaluating their global extent and occurrence patterns. A summary of wide field-of-view (several to tens of degrees) soft X-ray imaging is provided including slumped micropore microchannel reflectors, simulated images, and recent flight results.

A study of the excitation energy dependence of resonant X-ray emission spectra across the O1s absorption edge in combination with X-ray absorption spectroscopy and density functional theory reveals the site-specific valence electronic structure of liquid acetic acid under ambient conditions.

A new type of collector optics was developed for grazing incident x-ray emission spectrometer. The collector optics used two cylindrical mirrors to add two extra light paths while keeping the center light path that directly illuminates the grating. The design and properties of the spectrometer using the triple-path collector optics were evaluated using ray-tracing simulations, and validity of this design in terms of throughput and energy resolution was confirmed by the experimentally obtained spectra.

We use resonant X-ray emission spectroscopy and model calculations to quantify the ligand: heme-Fe energy structure of aqueous myoglobins. For reduced (Fe 2+) and oxidized (Fe 3+) states, the removal or addition of an electron primarily involves charge changes on the ligand-site, and not the Fe-site. The results indicate a finite positive/negative charge-transfer energy Delta between the heme-Fe 3d and ligand valence electronic states for Fe 2+/Fe 3+. Thus, the energy difference between the ligand and Fe 3d states (+ Delta ...

In this paper we present in a first part the latest results of our group which are in relation with the
study of DNA damages inflicted by low energy electrons (0-20 eV) in ultra-high vacuum as well as in
air under atmospheric conditions. A short description of the drop-casting technique we developed to
produce thin and nanometre-scaled DNA layers onto graphite sheets is given. We provide the
absolute cross-section for loss of supercoiled topology of plasmid DNA complexed with 1,3-
diaminopropane (Dap) in the vacuum under 10 eV electron impact and suggest a specific pathway for
the dissociation of the transient negative ion formed by resonant capture of such a low energy
electron (LEE) by the DNA’s phosphate group when complexed to Dap. Well-gauged DNA-Dap layers
with various nanometre-scaled thicknesses are used to evaluate the effective attenuation length of
secondary photo-LEEs in the energy range (0-20 eV). The values of 11-16 nm for DNA kept under
atmospheric conditions are in good agreement with the rare literature data available and which are
stemming from computer simulations. In a second part, we describe the method we have developed
in order to expose liquid samples of plasmid DNA to ultra-soft X-rays (Al Kalpha line at 1.5 keV) under
hydroxyl radical scavenging conditions. We provide an experimentally determined percentage of
indirect effects in aqueous medium kept under standard conditions of 94.7 ± 2.1 % indirect effects; in
satisfactory agreement with the data published by others (i.e. 97.7%) relative to gamma irradiation
of frozen solutions (Tomita et al., 1995).

Homogeneous plasma columns with ionization levels typical of megaampere discharges are created by rapidly heating gas-filled 520−μm-diameter channels with nanosecond rise time current pulses of 40 kA. Current densities of up to 0.3  GA cm−2 greatly increase Joule heating with respect to conventional capillary discharge Z pinches, reaching unprecedented degrees of ionization for a high-Z plasma column heated by a current pulse of remarkably low amplitude. Dense xenon plasmas are ionized to Xe28+, while xenon impurities in hydrogen discharges reach Xe30+. The unique characteristics of these hot, ∼300:1 length-to-diameter aspect ratio plasmas allow the observation of unexpected spectroscopic phenomena. Axial spectra show the unusual dominance of the intercombination line over the resonance line of He-like Al by nearly an order of magnitude, caused by differences in opacities in the axial and radial directions. These plasma columns could enable the development of sub-10-nm x-ray lasers.

We use resonant X-ray emission spectroscopy and model calculations to quantify the ligand: heme-Fe energy structure of aqueous myoglobins. For reduced (Fe2+) and oxidized (Fe3+) states, the removal or addition of an electron primarily involves charge changes on the ligand-site, and not the Fe-site. The results indicate a finite positive/negative charge-transfer energy Δ between the heme-Fe 3d and ligand valence electronic states for Fe2+/Fe3+. Thus, the energy difference between the ligand and Fe 3d states (+Δ or -Δ) determines the charge properties of myoglobins. The study provides a reliable method for characterizing ligand-metal binding of biological systems in solution.

An extremely high resolution flat field type slit less soft x-ray emission spectrometer has been designed and constructed for the long undulator beamline BL07LSU in SPring-8. By optimizing the ruling parameters of two cylindrical gratings, a high energy resolution ΔE &lt; 100 meV and/or an E∕ΔE ~ 10 000 are expected for the energy range of 350 eV - 750 eV taking into account the broadening by the spatial resolution (25 μm) of a CCD detector. A coma-free operation mode proposed by Strocov et al., is also applied to eliminate both defocus and coma aberrations. The spectrometer demonstrated experimentally that E/ΔE = 10 050 and 8046 for N 1s (402.1 eV) and Mn 2p (641.8 eV) edges, respectively.

The structure of liquid water is presently under intense debate. We summarize the historical development of the present description of water and the controversy surrounding the X-ray absorption spectroscopy (XAS) study of Wernet et al. [Ph. Wernet et al., Science 304 (2004) 995]. In order to provide further insight into the connection between X-ray spectroscopy and the structure of the hydrogen bonding network, we report new data comprising high resolution oxygen K-edge X-ray emission spectra (XES) of liquid water. We observe two distinct narrow lone-pair derived peaks, assigned, respectively, to tetrahedral and strongly distorted hydrogen-bonded species; the assignment is based on comparison with ice and gas phase spectra, temperature dependent measurements, excitation energy dependence and theoretical simulations. We estimate a 2:1 ratio between distorted and tetrahedral species at room temperature and discuss what this implies in connection to the previous XAS study and in terms of liquid water structure.We observe two distinct, narrow lone-pair derived peaks in high-resolution X-ray emission spectra (XES) of liquid water, which we assign respectively to tetrahedral and strongly distorted hydrogen-bonded species. We estimate a 2:1 ratio between distorted and tetrahedral species at room temperature and discuss what this implies in connection to a previous, much debated X-ray absorption spectroscopy (XAS) study and in terms of liquid water structure.