Gamma rays produced by inverse Compton scattering in the Super-ACO storage ring free electron laser

The inverse Compton scattering between positron bunches and the free electron laser (FEL) of the Super-ACO storage ring generates a collimated and tunable gamma-ray beam. The use of the FEL instead of an external conventional laser, automatically provides the transverse alignment and synchronisation of the electron and optical beams. The Super-ACO FEL is operated in the 300–430 nm range at 800 MeV with a high repetition rate (8 MHz) and an average transmitted power of 300 mW at 350 nm. High energy gamma-rays of 35 MeV are produced with a rate of 1.5×10⁷ photons/s and good monochromaticity (about 10%).     

C2H3Cl分子团簇内部离子-分子反应产生C4H5Cl+的研究

用同步辐射对（Ｃ２Ｈ３Ｃｌ）２分子团簇进行了光电离研究，发现该团簇内部发生了离子－分子化学反应，生成了十分稳定的反应产物Ｃ４Ｈ５Ｃｌ＾＋，不再是ｖａｒｄｅｒＷａａｌｓ弱键络合物，本文对反主尖机理进行了初步探讨。     

Chemical bonding effect in electron scattering by gaseous molecules

The experimental intensity of 30 keV electron small angle scattering by a gaseous molecule is much different from the calculation using usual independent atom model. This is due to the rearrangement of electron distribution in a molecule by the formation of chemical bonds, and is called chemical bonding effect (CBE). The molecules studied are mainly hydrocarbons such as methane, acetylene, ethane, etc. and some non-hydrocarbons. The measurement was carried out on both elastic and total scattering and the effect was found for not only elastic but also inelastic scattering. The effect is relatively large for hydrogen rich molecules as H₂O, NH₃ and hydrocarbons, but is essentially related to the number of atoms contained in molecules. The origin of CBE will attribute mainly to the concentration of inner atomic electrons resulting from chemical bonding.     

Incoherent scattering of 59.54 keV γ-rays at small momentum transfers

Whole atom differential incoherent scattering cross sections for 59.54 keV γ-rays were measured for a number of elements in the region 29Z82 at scattering angles 90, 60, 45 and 30° employing a reflection geometry set up and a graded shielding arrangement. A 6 cm³ HPGe detector was used to detect the scattered γ-rays. All the 49 cross sections reported in this paper constitute the first experimental measurement and serve to fill the existing gaps in the cross-section data. The comparison of the measured cross sections with Klein–Nishina theory shows electron binding effects becoming significantly large at small scattering angles and for high Z elements. Incoherent scattering functions S(x, Z), corresponding to momentum transfer values 3.395, 2.4, 1.84 and 1.242 Å⁻¹ were extracted from the measured cross sections and were compared with the theoretical predictions. The non-relativistic Hartree–Fock theory is found to be comparatively better than the Thomas–Fermi model. At small momentum transfer values and for high Z elements experimental values deviate more from Hartree–Fock theory also suggesting the need for a more rigorous second-order S-matrix calculations.     

VUV photoionization of acetamide studied by electron/ion coincidence spectroscopy in the 8-24 eV photon energy range

A VUV photoionization study of acetamide was carried out over the 8-24 eV photon energy range using synchrotron radiation and photoelectron/photoion coincidence (PEPICO) spectroscopy. Threshold photoelectron photoion coincidence (TPEPICO) measurements were also made. Photoion yield curves and branching ratios were measured for the parent ion and six fragment ions. The adiabatic ionization energy of acetamide was determined as I.E. (1²A′) = (9.71 ± 0.02) eV, in agreement with an earlier reported photoionization mass spectrometry (PIMS) value. The adiabatic energy of the first excited state of the ion, 1²A″, was determined to be ≈10.1 eV. Assignments of the fragment ions and the pathways of their formation by dissociative photoionization were made. The neutral species lost in the principal dissociative photoionization processes are CH₃, NH₂, NH₃, CO, HCCO and NH₂CO. Heats of formation are derived for all ions detected and are compared with literature values. Some astrophysical implications of these results are discussed.     

Crystal structure and electron density in the apatite-type ionic conductor La9.71(Si5.81Mg0.18)O26.37

Crystal structure and electron density in the apatite-type ionic conductor La_9.71(Si_5.81Mg_0.18)O_26.37 have been investigated at 302, 674 and 1010 K by Rietveld refinement and a whole-pattern fitting approach based on the maximum-entropy method (MEM) using synchrotron X-ray powder diffraction data. Second harmonic generation measurements indicated that the space group of this material is centrosymmetric. Among the possible hexagonal groups P6₃/m, P6₃ and the former is correct for La_9.71(Si_5.81Mg_0.18)O_26.37. Rietveld refinements suggested an oxygen interstitial site (0.03,0.15,0.85) near the hexagonal axis. MEM analyses revealed that the Si_0.97Mg_0.03 atom has covalent bonds with four adjacent oxygen atoms to form a tetrahedron. The oxygen O4 atom located at the 2a site (0.0,0.0,1/4) exhibited large atomic displacement parameters along the c axis and electron density mapping also indicated the wide distribution consistent with migration of oxygen ions in this direction.     

Photon cascade luminescence in CaAl12O19:Pr, Cr

In this report, the Cr³⁺ ion was chosen as a co-dopant to modify the unpractical photon cascade emission properties of Pr³⁺-doped CaAl₁₂O₁₉ phosphors, which emit one near-UV photon from the ¹S₀ state followed by visible photons from the ³P₀ state, into phosphors that emits two visible photons through energy transfer. The photon cascade emission process via energy transfer and the transfer mechanisms were systemically investigated by luminescence spectra and dynamics using synchrotron radiation as one of the excitation sources. The internal visible quantum efficiency of CaAl₁₂O₁₉:Pr, Cr was estimated and compared with CaAl₁₂O₁₉:Pr and the drawback to obtain the visible quantum efficiency higher than unit for CaAl₁₂O₁₉:Pr, Cr as a practical VUV phosphor was also discussed.     

Elucidation of the relationships of structure-process-property for different ethylene/α-olefin copolymers during film blowing: An in-situ synchrotron radiation X-ray scattering study

The copolymerization of ethylene and different α-olefins could result in polyethylene (PE) with different structural topologies, and lead to polyethylene products with different macroscopic performances. Herein, three different polyethylene samples, namely low-density polyethylene (l-PE), metallocene catalyzed ethylene-hexene copolymer (h-PE) and ethylene-octene copolymer (o-PE), were selected as representatives to construct the structure-process-property relationship during film blowing. The detailed crystal-based network evolution during film blowing was first characterized by in-situ synchrotron radiation X-ray scattering. The crystallization process of l-PE film is determined by the coupling effects of temperature and flow, while those of h-PE and o-PE films are dominated by the temperature. Furthermore, the hierarchical crystal structure from the molecular scale to micrometers of final films and segmental dynamics were systematically characterized by multiple ex-situ characterization techniques, i.e. Solid-State NMR, FTIR, SEM. l-PE film shows the crystalline morphology of the row-nucleated structure, whereas h-PE and o-PE show spherulite-like superstructure with better mechanical properties. The current study tentatively constructs the relation of primary chemical structure, microstructural evolution and macroscopic performances of different polyethylene copolymers during film blowing.     

Liquid-crystalline ordering in polymeric networks as studied by polarized raman scattering

Uniaxially oriented polymer networks are produced by photoinitiated bulk polymerization of liquid-crystalline diacrylates. The order parameters S₂ and S₄ of the mesogenic moieties in these networks are simultaneously determined by means of the polarized Raman scattering technique. It yields an estimate of the orientation distribution function for different polymerization temperatures and for different lengths of the alkyl chain, present as a spacer in the liquid-crystalline diacrylate.     

Thermoluminescence and synchrotron radiation studies on the persistent luminescence of BaAl2O4:Eu,Dy

The persistent luminescence materials, barium aluminates doped with Eu²⁺ and Dy³⁺ (BaAl₂O₄:Eu²⁺,Dy³⁺), were prepared with the combustion synthesis at temperatures between 400 and 600 °C as well as with the solid state reaction at 1500 °C. The concentrations of Eu²⁺/Dy³⁺ (in mol% of the Ba amount) ranged from 0.1/0.1 to 1.0/3.0. The electronic and defect energy level structures were studied with thermoluminescence (TL) and synchrotron radiation (SR) spectroscopies: UV-VUV excitation and emission, as well as with X-ray absorption near-edge structure (XANES) methods. Theoretical calculations using the density functional theory (DFT) were carried out in order to compare with the experimental data.     

Modulating spin delocalization in conjugated nitroxides: 2-(N-aminoxyl-N-tert-butyl)-benzothiazole

The first controlled synthesis of the title radical, 1, was achieved by oxidation of a hydroxylamine precursor; the radical itself can thus readily be isolated, studied by ESR and UV-vis, and compared to results of computational modeling. The benzothiazole ring induces substantial delocalization of the nitroxide spin density (a(NO) = 9.2 G, a(ring N) = 2.7 G, about 10% more than is seen in the benzimidazole nitroxide analog.     

Diffusion behavior of pharmaceutical O/W microemulsions studied by dynamic light scattering

Dynamic light scattering experiments have been performed at various concentrations, of pharmaceutical oil-in-water microemulsions consisting of Eutanol G as oil, a blend of a high (Tagat O2) and a low (Poloxamer 331) hydrophilic–lipophilic balance surfactant, and a hydrophilic phase (propylene glycol/water). We probe the dynamics of these microemulsions by dynamic light scattering. In the measured concentration range, two modes of relaxation were observed. The faster decaying mode is ascribed classically to the collective diffusion D _c (total droplet number density fluctuation). We show that the slow mode is also diffusive and suggest that its possible origin is the relaxation of polydispersity fluctuations. The diffusion coefficient associated with this mode is then the self-diffusion D _s of the droplets. It was found that D _c and D _s had opposite volume fractions of oil plus surfactants (ϕ) dependence and a common limiting value D ₀ for ϕ=0. Average hydrodynamic radius (R _h=10.5 nm) of droplets was calculated from D ₀. R _h is supposed to compose the inner core, a surfactant film including possible solvent molecules, which migrate with the droplet. The concentration dependence of diffusion coefficients reflects the effect of hard sphere and the supplementary repulsive interactions which arises due to loss of entropy, when absorbed chains of surfactant intermingle on the close approach of the two droplets. This mechanism could also explain the observed stability of our systems. The estimated extent of polydispersity is 0.22 from the amplitude of slower decaying mode. The polydispersity in microemulsion systems is dynamic in origin. Results indicate that the time scale for local polydispersity fluctuations is at least three orders of magnitude longer than the estimated time between droplet collisions.     

Quantumness of correlations and Maxwell's demon in molecular excitations created by neutron scattering

Nonclassical correlations known as entanglement, quantum discord, quantum deficit, measurement‐induced disturbance, quantum Maxwell's demon, etc., may provide novel insights into quantum‐information processing, quantum‐thermodynamics processes, open‐system dynamics, quantum molecular dynamics, and general quantum chemistry. We study a new effect of quantumness of correlations accompanying collision of two distinguishable quantum systems A and B, the latter being part of a larger (interacting) system B + D. In contrast to the common assumption of a classical environment or “demon” D, the quantum case exhibits striking new qualitative features. Here, in the context of incoherent inelastic neutron scattering from H‐atoms which create molecular excitations (vibration, rotation, translation), we report theoretical and experimental evidence of a new phenomenon: a considerably reduced effective mass of H, or equivalently, an anomalous momentum‐transfer deficit in the neutron‐H collision. These findings contradict conventional theoretical expectations even qualitatively, but find a straightforward interpretation in the new theoretical frame under consideration. © 2015 Wiley Periodicals, Inc.     

Spin-gap magnetic response in (Yb, Lu)B12

To clarify the role of Yb-Yb correlations in the formation of the gap-like excitation spectrum of YbB₁₂, the spin dynamics of strongly diluted Yb_0.25Lu_0.75B₁₂ have been studied by inelastic neutron scattering in a wide temperature range. The data indicate that the spin gap is not suppressed by the dilution process even for large concentrations of Lu. However, the breaking-down of the Yb-sublattice periodicity leads to a strong smearing of the low-energy features and to a moderate suppression of the high-energy peak in the magnetic spectral response of YbB₁₂. The interrelation of the spin and charge gaps is discussed.     

利用康普顿散射分析碳化硅陶瓷在高温下使用氧化后组成的变化

用波长色散X射线荧光光谱仪,通过测量散射体(样品)对铑的康普顿散射线(RhKα-C)强度的变化,实现了碳化硅陶瓷在高温下使用时氧化情况的监控。用一套8只碳化硅校准样品建立了康普顿散射强度与样品平均原子序数之间关系的数学模型。利用此模型计算了碳化硅氧化后组成含量的变化。结果表明:用此方法测得的样品中碳、硅及氧的相对含量与X射线光电子能谱法所测结果相符,两者间的相对偏差均小于1%。据此认为,此方法所测得的数据是可以接受的。     

Measurement of the Compton profiles of CH4 and C2H4 by high energy electron impact spectroscopy

We present a new experimental determination of the Compton profiles of CH₄ and C₂H₄ molecules using high energy electron impact. The observable q range has been extended up to 10 au (6 au for C₂H₄). Good agreement is found with an earlier X-ray scattering experiment and with new theoretical calculations.     

Elastic scattering of low-energy electrons by N2 including the effect of target electronic correlation

A procedure to use configuration-interaction (CI) target wave-functions in the electron–molecule collision theory is applied to study the elastic e⁻–N₂ scattering in the (5–20) eV incident energy range. Correlated static and exchange contributions to the interaction potential are presented. Two different atomic basis sets are used. Differential cross sections (DCS) obtained by using Hartree–Fock or CI wave-functions are presented and compared. In the CI case, single and double, and single, double and triple excitations are considered. The effect of electron correlation is analyzed in all the cases. The continuum wave-functions were obtained via the Schwinger variational iterative method. The influence on the DCS of both the size of the atomic basis set and the inclusion of higher-order excitations in the CI calculation is discussed.     

The system ZrO2CaO studied by the electron spin resonance of Mn2+ ions

We have used the electron spin resonance of Mn²⁺ ions to study the zirconia-calcia system from 9 to 60 mole% CaO. With the exception of single crystals of calcia-stabilized zirconia (CSZ) with 15 and 20 mole% CaO, the experiments were carried out on polycrystalline samples. From the different values measured for the hyperfine coupling constant A with increasing amount of calcia, we have deduced that Mn²⁺ substitutes for Ca²⁺ in the three following host lattices: cubic CSZ, CaZrO₃, and CaO.     

Magnetic properties of Co2V2O7 single crystals grown by flux method

Based on the phase diagram of CoO–V₂O₅ system, single crystals of Co₂V₂O₇ are grown using V₂O₅ as self-flux at a slow cooling rate. The quality of grown crystals is analyzed by X-ray powder diffraction and electron probe microanalysis techniques. Magnetic properties are investigated by means of susceptibility, magnetization, and heat capacity measurements. Our experimental results suggest that Co₂V₂O₇ is a three-dimensional antiferromagnet, in which two magnetic transitions may occur at low temperature and a spin-flop-like transition may occur at the applied field along the b-axis. By contrast to Ni₂V₂O₇, it is suggested that similar and different magnetic properties may arise from their similar crystal structures and different magnetic ions, respectively.     

Molecular structures of (SiCl3)2CH2 and (SiCl3)2CCl2 as studied by electron diffraction

An electron diffraction analysis of the molecular structures of 1,1,1,3,3,3-hexachloro-1,3-disilapropane and octachloro-1,3-disilapropane has been carried out. Deviations from the staggered conformation are indicated. The data may be approximated by models with C₂ symmetry and a small tilt of the SiCl₃ groups. The main bond lengths (r_g) and bond angles obtained for (SiCl₃)₂ CH₂ are: SiCl, 202.7(4); SiC, 186.6(6); CH, 109.8(24) pm, ClSiCl, 107.9(1); SiCSi, 118.3(7)°; and for (SiCl₃)₂CCl₂: SiCl, 202.0(4); SiC, 190.2(9); CCl, 179.6(9) pm; ClSiCl, 109.5(1); SiCSi, 120.6(9); ClCCl, 110.9(16); SiCCl, 106.3(3)°.