Opportunities for resonant elastic X-ray scattering at X-ray free-electron lasers

X-ray Free-Electron Lasers (FELs) are beginning to deliver a revolution in X-ray experiments, thanks to their ultra-bright (peak brightness exceeding 10³³ photons/s/mm²/mrad²/0.1%BW), ultrashort (down to a few fs), spatially coherent X-ray pulses. Presently operational facilities cover wide spectral ranges, from the VUV and soft X-ray wavelengths of FLASH in Hamburg (down to 4.2 nm), to the hard X-rays delivered by the LCLS in Stanford (wavelengths of 0.15 nm or shorter). The basic properties of the new sources are briefly reviewed, and the impact on resonant scattering experiments is discussed. The perspective of investigating ultrafast magnetism, and, more generally, the time-dependent response of strongly correlated electron systems, in a pump-and-probe mode at the L edges of 3d transition metals, would be very attractive. In the hard X-ray range, the very recent proposal of self-seeded X-ray FELs, with 10⁻⁵ intrinsic bandwidth, tunable wavelength, 100 fs pulses and number of photons per pulse of order 10¹² also opens exciting possibilities for resonant scattering.     

Commissioning experience with insertion devices at PETRA III

PETRA III is a new hard X-ray synchrotron radiation source, operating at 6 GeV with a beam current of up to 100 mA and extremely low horizontal emittance of 1 nm rad. Such low emittance is achieved by using two 100 m long damping wiggler sections which reduce the emittance by a factor of 4. Altogether the damping sections contain 20 wigglers of 4m length each. The emitted synchrotron radiation power produced by wigglers amounts to 420 kW at 100 mA beam current in total. In the new octant of PETRA III, there are 14 undulator beamlines, with a brilliance up to 10²¹ (s mrad² mm² 0.1% BW)⁻¹ which cover an energy range from 0.3 keV to more than 100 keV. The low emittance raises very high requirements to the field quality of the insertion devices. At first, it should not affect the positron beam trajectory. Secondly, the spectral properties of the radiation created, like the intensity of higher harmonics, should not be limited by the undulator field quality, but by the beam emittance effects in order to have some reserve for future machine upgrades or possible radiation demagnetization. This paper presents the current status of PETRA III insertion devices and describes intermediate commissioning results like impact of IDs on the positron beam orbit or photon beam and radiation problems.     

The correlation timescale of the X-ray flux during the outbursts of soft X-ray transients

Recent studies of black hole and neutron star low mass X-ray binaries (LMXBs) show a positive correlation between the X-ray flux at which the low/hard(LH)-to-high/soft(HS) state transition occurs and the peak flux of the following HS state. By analyzing the data from the All Sky Monitor (ASM) onboard the Rossi X-ray Timing Explorer (RXTE), we show that the HS state flux after the source reaches its HS flux peak still correlates with the transition flux during soft X-ray transient (SXT) outbursts. By studying large outbursts or flares of GX 339-4, Aql X-1 and 4U 1705-44, we have found that the correlation holds up to 250, 40, and 50 d after the LH-to-HS state transition, respectively. These time scales correspond to the viscous time scale in a standard accretion disk around a stellar mass black hole or a neutron star at a radius of ∼10^4–5 R _g, indicating that the mass accretion rates in the accretion flow either correlate over a large range of radii at a given time or correlate over a long period of time at a given radius. If the accretion geometry is a two-flow geometry composed of a sub-Keplerian inflow or outflow and a disk flow in the LH state, the disk flow with a radius up to ∼10⁵ R _g would have contributed to the nearly instantaneous non-thermal radiation directly or indirectly, and therefore affects the time when the state transition occurs.

     

X-ray spectra induced by <Superscript>129</Superscript>Xe<Superscript><Emphasis Type="Italic">q</Emphasis>+</Superscript> impacting the metal surface

Using the slow highly charged ions ¹²⁹Xe ^q+ (q = 25, 26, 27; initial kinetic T ₀⩽4.65 keV/a.u.) to impact Au surface, the Au atomic Mα 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 Mα-X-ray spectra, Au atomic N-level lifetime is estimated at about 1.33×10⁻¹⁸ s based on Heisenberg uncertainty relation. Supported by the National Natural Science Foundation of China (Grant Nos. 10574132, 10274088 and 10405025), the Talent Introduction Project of Xianyang Normal University (Grant No. 05XSYK103) and the Education Commission Foundation of Shaanxi Province (Grant No. 04JK300)     

Characterization of collisionally pumped optical-field-ionization soft X-ray lasers

We give an overview of recent experimental results on optical-field-ionization collisional soft X-ray lasers developed at LOA. By focusing a 30-fs, circularly polarized Ti-sapphire laser pulse at an intensity of up to 8×10¹⁷ Wcm^-2 into a low-density gas cell containing Xe or Kr, we produced a few mm long plasma column for soft X-ray amplifier. Saturated amplification has been achieved on the 4d⁹5d(¹S₀)–4d⁹5p(¹P₁) transition at 41.8 nm in Xe⁸⁺, and on the 3d⁹4d(¹S₀)–3d⁹4p(¹P₁) transition in Kr⁸⁺ at 32.8 nm. Under optimum pumping conditions the Xe⁸⁺ laser provides about (5±2)×10⁹ photons per pulse whilst the Kr⁸⁺ laser delivers up to (2.5±1)×10⁹ photons per shot. The repetition rate of these soft X-ray lasers is 10 Hz. The beam wavefront of the Xe⁸⁺ laser has been measured by a Shack–Hartmann soft X-ray wavefront sensor, and the pulse duration by a cross-correlation technique. PACS 42.55.Vc; 32.30.Rj; 52.50.Jm     

Preparation of48V source for measurements of lineshapes of annihilation radiations and positron lifetimes

The preparation of the⁴⁸V positron source induced in a 1 μm thick Ti foil by (³He, pxn) reaction with a cyclotron is described. This source is very convenient for measurements of lineshapes of annihilation radiations and positron lifetimes at low or high temperatures, in a vacuum or for liquid metals. The absence of the mixing of long lifetime components is also convenient for the study of defects.     

X-ray spectroscopy measurements of laser compressed,argon filled shells

Argon X-ray lines have been used in the past to diagnose laser-compressed targets. We extend such measurements to: (a) very high densities (ρ ≈ 9 gcm^-3) obtained when imploding small shells with short laser pulses, and (b) lower densities but higher πR values (≈4 mg cm^-2) obtained with large DT-Ar filled shells, imploded with long laser pulses. The 24-beam OMEGA laser has been used with 4–5 TW, 100 ps pulses in (a), and 1.5–2 TW, 1 ns pulses in (b).     

Mössbauer and XRD study of pulse plated Fe–P and Fe–Ni thin layers

⁵⁷Fe conversion electron Mössbauer spectroscopy, X-ray diffraction, electrochemical and magnetic measurements were used to study pulse electroplated Fe–P and Ni–Fe coatings. XRD and ⁵⁷Fe CEMS measurements revealed the amorphous character of the novel pulse plated Fe–P alloys. CEM spectra indicated significant differences in the short range order and in the magnetic anisotropy between the Fe–P deposits pulse plated at medium long deposition time (t _on?=?2 ms), with short relaxation time (t _off?=?9 ms) and low current density (I _p?=?0.05 Acm^?2) or at short deposition time (t _on?=?1 ms) with long relaxation time (t _off?=?250 ms) and high current density (I _p?=?1.0 Acm^?2). The broad peaks centred around the fcc reflections in XRD of the pulse plated Ni-22 wt.% Fe deposit reflected a microcrystalline Ni–Fe alloy with a very fine, 5–8 nm, grain size. The CEM spectrum of the pulse plated Ni-22 wt.% Fe coating corresponded to a highly disordered solid solution alloy containing a minute amount of ferrihydrite. Extreme favourable soft magnetic properties were observed with these Ni–Fe and Fe–P pulse plated thin layers.     

Structural characterization of Rh/pumice SMAD catalysts

The structure of Rh/pumice catalysts prepared by the SMAD (Solvated Metal Atoms Dispersion) technique at different metal loadings has been investigated by EXAFS (Extended X-ray Absorption Fine Structure Spectroscopy), XPS (X-ray Photoelectron Spectroscopy), SAXS (Small-Angle X-ray Scattering), WAXS (Wide-Angle X-ray Scattering) and TEM (Transmission Electron Microscopy). According to EXAFS and XPS, a fraction of the Rh atoms is oxidised, but a noticeable part is also present as Rh ⁰. The Rh oxidation is attributed to the interaction of the Rh atoms with the hydroxyls of the support; after the formation of the oxide, the nucleation of metallic rhodium becomes possible. The WAXS data do not show evidence of rhodium fcc crystallites; the metal-bearing particles are probably amorphous and/or very small, as results from the SAXS and TEM data analysis. The disagreement between the latter two techniques, resulting in a small-angle determination of the average size of the particles that is about half that of TEM in the catalyst with the higher Rh loading, is acknowledged and discussed. Preliminary catalytic tests are described, demonstrating the suitability of using a low surface area support for the preparation of SMAD catalysts. Received 2 February 1999     

Highly water resistant surface coating by fluoride on long persistent Sr4Al14O25:Eu/Dy phosphor

A novel and efficient method of providing moisture resistance of inorganic particles such as divalent europium activated strontium aluminate phosphors (Sr₄Al₁₄O₂₅:Eu²⁺/Dy³⁺) was developed by firing the phosphor in the presence of appropriate amount of ammonium fluoride at a temperature of 600-700 °C. Scanning electron microscopy, X-ray diffraction, FT-IR, EDAX and Photoluminescence measurements were carried out to characterize the uncoated and coated samples. The pH measurements were carried out for the water resistivity measurements. The phosphor particles became coated with a moisture-impervious thin coating that did not suppress the luminescence of the phosphor and can withstand complete immersion in water for long periods of time, showing very high water resistivity.     

BaFBr:Eu2+ nanophosphor-SiO2 hybrid entrapped in Anodise Alumina membrane pores array

Sol–gel template method has been used to prepare BaFBr:Eu²⁺ nanophosphor-SiO₂ hybrid entrapped within the nanopores array (of about 200 nm size) of a comercial anodized alumina (AA) membrane. Structural and morphological measurements using electron microscopy (SEM) and X-ray diffraction (XRD) have shown the presence of the BaFBr:Eu²⁺ nanophosphor in the silica xerogel entrapped within the nanopores array; photoluminescence and X-ray excited luminescence measurements have shown Eu²⁺ luminescence at 395 nm accompanied by a broad band due to AA membrane. The method assures a relatively uniform spreading of the BaFBr nanophosphor into the AA membrane pores array without the nanoparticles agglomeration. Preliminary imaging tests have shown a spatial resolution in the micrometer range and even in the submicrometer range can be expected. As BaFBr:Eu²⁺ is a very efficient X-ray phosphor the material might be used as X-ray micro-imaging detector.     

三倍频激光等离子体X射线转换研究

利用“星光Ⅱ”高功率激光装置三倍频激光（波长０.３５μｍ,能量５—９０Ｊ,焦斑直径约２００μｍ,脉冲宽度４００—８００ｐｓ）辐照多种材料（Ｃ,Ａｌ,Ｃｕ,Ａｕ）靶,对于不同激光功率密度,研究软Ｘ射线转换和发射能谱．结合０.３５μｍ激光辐照Ａｌ靶的质量烧蚀率和等离子体喷射速度与激光功率密度的定标关系进行数值模拟,对于激光功率在１０^１３—１０^１５Ｗ／ｃｍ²理论模拟结果与实验结果符合得很好 关键词：     

Measurement of orientation crystallization rates of linear polymers by means of dynamic X-ray diffraction technique. II. Frequency dispersion of strain-induced crystallization coefficient of natural rubber vulcanizates in subsonic range

The orientation crystallization behavior of natural rubber vulcanizates was investigated by means of a dynamic X-ray diffraction technique utilizing the half-circle sector technique. The frequency dependence of dynamic diffraction intensities from diatropic and paratropic crystal planes, (002) and (200) planes, was observed over a frequency range from 10^?3 to 10¹ Hz as a function of temperature, degree of cross-linking, static extension ratio, and dynamic strain amplitude.

The frequency dependence of the dynamic X-ray diffraction gives two dispersion regions around 10^?2 and 10^?1 Hz. The phase angle between the dynamic X-ray diffraction and dynamic strain of a bulk specimen is definitely positive; i.e., the dynamic strain of the specimen is always behind the dynamic orientation crystallization.

The frequency dispersion at low frequencies, around 1WZ Hz is very obvious for the (200) crystal plane and shifts somewhat to higher frequencies under those conditions that increase the mobility of self-diffusion of rubber molecules, i.e., increase of temperature and decreases of extension ratio and degree of cross-linking. The frequency dispersion at high frequencies, around 10¹ Hz, is rather obvious for the (002) crystal plane and does not shift appreciably under the experimental conditions.     

Effects of an ultrashort prepulse on soft X-ray generation from an aluminium plasma produced by femtosecond Ti:Sapphire laser pulses

The influence of a prepulse on soft X-ray emission in the range of 50–200 from an aluminium plasma produced by 130 fs Ti: Sapphire laser pulses with an intensity of 10¹⁴ W/cm² at normal incidence is studied. An ultrashort prepulse with an intensity of 10¹³ W/cm² significantly enhances soft X-ray emission when there is a long time separation ( > 100 ps) between the prepulse and an intense main pulse. It is also observed for the first time that a prepulse with a short pulse time separation can slightly reduce soft X-ray emission, contrary to the previous work done using 248 nm laser pulses. This can be explained qualitatively in terms of the dependence of absorption on the length scale.     

Mössbauer Study of Nanocrystalline ε-Fe3−x Co x N System

Five clays from four different deposits in the Ivory Coast (Adattié, Nieki, Grand-Bassam, Nigui-Saff) were studied by ⁵⁷Fe Mössbauer spectroscopy and electron paramagnetic resonance (EPR) at room temperature. Their chemical compositions were determined by X-ray fluorescence and the most important crystalline phases were identified by X-ray diffraction. In these natural clays, kaolinite is the dominant mineral phase with minor amounts of other minerals including quartz, haematite, goethite, lepidocrocite and illite. Room-temperature ⁵⁷Fe Mössbauer spectra of the samples from Nieki, Adattié and Nigui-Saff show mainly a broad quadrupole-split doublet which indicates that iron is essentially present as Fe(III). Samples from Grand-Bassam contain important amounts of goethite (α-FeOOH) and lepidocrocite (γ-FeOOH). Some samples from Nigui-Saff contain large amounts of haematite. Clays from Nieki and Adattié are characterised by very low concentrations of iron oxides or hydroxides, and by small amounts of structural Fe(II) in the kaolinite lattice. Oxidation states and lattice sites of structural iron in the kaolinites were determined by ⁵⁷Fe Mössbauer spectra recorded after iron extraction with dithionite-citrate-bicarbonate (DCB). The results were confirmed by electron paramagnetic resonance (EPR) measurements.     

E2 nuclear resonance effects in pionic and kaonic atoms

The attenuation due to the E2 nuclear resonance effect has been measured in hadronic atoms using pions with ¹¹¹Cd and ¹¹²Cd, and for kaons with ¹²²Sn. Energies of the relevant X-ray and γ-ray transitions and of the X-ray cascade intensities have also been measured so as to give a self-consistent set of information. The results are found to be in very good agreement with theoretical calculations.     

Synthesis and characterization of SWNT-heavy alkali metal intercalation compounds,effect of host SWNTs materials

Singlewall carbon nanotubes (SWNTs) produced by electric-arc and laser ablation methods were characterized by X-ray diffraction before and after the reaction with alkali metals (M=K, Rb, and Cs). Reaction with annealed SWNTs gave MC₈ composition at saturation. The alkali metal lattice showed short range order incommensurate with graphene cylinders of SWNTs. X-ray diffractogram simulations have enabled the study of the influence of SWNTs structure on that of intercalation compounds. Chemically-purified bundles, constituted of open SWNTs, can be intercalated inside and between the tubes forming disordered structures. Annealed or pristine bundles were intercalated only between the tubes leading to short or long range ordered structure depending on host crystallinity and alkali metal (K, Rb or Cs). The expansion of the 2D SWNTs lattice after intercalation is comparable to graphite intercalation compounds. Some 2D arrangements of SWNTs and K atoms are proposed and discussed to reproduce XRD results. ¹³C NMR and ESR studies of annealed doped SWNTs emphasize the fact that the intercalation compounds of SWNTs are metallic.     

高空核爆炸下大气的X射线电离及演化过程数值模拟

利用数值模拟程序模拟了不同高度核爆炸下大气的X射线电离及演化过程.结果表明: X射线电离产生的电子数密度在射线到达后约100 ns时刻达到峰值, 峰值数密度随着到裸核区距离的增加而减小;电子具有较长的寿命, 电子寿命随着到裸核区距离的增加而增大; X射线电离空气产生正离子O⁺, O₂⁺, N₂⁺,爆高为120 km情况下 O⁺的峰值数密度与O₂⁺的相近,能维持约1 s. X射线对空气的电离影响范围在数十千米以内,在距裸核区较近的区域, 爆高为80 km时产生的电子峰值数密度比爆高为120 km时的电子峰值数密度高, 在距裸核区较远的区域则相反.     

High pressure of solid noble gases in metals

The fact that noble gas ions implanted in metals with concentrations of a few percent precipitate at room temperature as solid bubbles under high pressure with a structure epitaxial with the host matrix (fcc or hcp) has been investigated recently. A brief survey of the results measured by transmission electron microscopy, glancing angle X-ray diffraction, energy-loss spectroscopy and positron annihilation is given. The main part of this paper deals with a study on⁸³Kr⁺ implanted in Al using Mössbauer spectroscopy. The results are as follows: the precipitates grow from 1.5 nm after implantation to 3.7 nm after 700 K annealing. The recoilless fractions can be fitted very well to a Debye model. On annealing. the characteristic Mössbauer temperature gradually decreases from 89 K to 64 K, the value for solid Kr at 1 bar. At the same time a decrease in the isomer shift is observed. Even after annealing at 700 K our experiments do not show melting in the temperature range 0–230 K.     

XPS and IR study of X-ray induced degradation of PVA polymer film

The X-ray induced compositional modification of a solvent cast polyvinyl alcohol [PVA, -(CH₂-HCOH)_n-] polymer film was studied using X-ray photoelectron (XPS) and transmission infra-red (IR) spectroscopies. While the -CH₂ group was stable, the alcoholic -COH moiety was unstable under the X-ray beam (Mg K α radiation: 1253.6 eV) and reached continuosly to produce three new C(1s) peaks assignable to carbonyl C=O (oxidation), carboxylate -COO (oxidative chain scission) and ether C-O-C linkages (crosslinking, dehydroxylation). Transmission FT-IR spectra of X-ray treated films showed the carbonyl stretch at 1700 cm^-1 and a loss of intensity in the O-H stretching mode near 3340 cm^-1. The results indicate that degradation occurs throughout the polymer bulk and is caused either directly, by X-ray photons, or by the secondary electrons generated within the polymer. The ease with which degration can be detected is sensitive to analyzer resolution, X-ray flux and precautionary measures.