Current Issue : July - September Volume : 2017 Issue Number : 3 Articles : 6 Articles
VZLUSAT-1 nanosatellite (scheduled launch in spring 2017 fromIndia) is a CubeSat mission which, besides other instrumentation,\ncontains X-ray desk to perform efficiency tests of the X-ray optics. In this article the analysis of potential observational candidates\nfor VZLUSAT-1 X-ray board is presented together with the suggestion of observational modes, laboratory measurements, and\nestimations of exposure settings....
GRB 130427A was the most luminous gamma-ray burst detected in the last 30 years.\nWith an isotropic energy output of 8.5Ã?â??1053 erg and redshift of 0.34, it combined very high energetics\nwith a relative proximity to Earth in an unprecedented way. Sensitive X-ray observatories such as\nXMM-Newton and Chandra have detected the afterglow of this event for a record-breaking baseline\nlonger than 80 million seconds. The light curve displays a simple power-law over more than three\ndecades in time. In this presentation, we explore the consequences of this result for a few models put\nforward so far to interpret GRB 130427A, and more in general the implication of this outcome in the\ncontext of the standard forward shock model....
The design of grating-based instruments to handle and condition coherent ultrafast\npulses in the extreme-ultraviolet is discussed. The main application of such instruments is the\nmonochromatization of high-order laser harmonics and free-electron-laser pulses in the femtosecond\ntime scale. Broad-band monochromators require the use of diffraction gratings at grazing incidence.\nA grating can be used for the spectral selection of ultrashort pulses without altering the pulse duration\nin a significant way, provided that the number of illuminated grooves is equal to the resolution.\nWe discuss here the design conditions to be fulfilled by a grating monochromator that does not\nincrease the pulse duration significantly longer than the Fourier limit....
Over the past decade, the advances in grating-based soft X-ray spectrometers have revolutionized\nthe soft X-ray spectroscopies in materials research. However, these novel spectrometers are mostly\ndedicated designs, which cannot be easily adopted for applications with diverging demands. Here we\npresent a versatile spectrometer design concept based on the Hettrick-Underwood optical scheme that\nuses modular mechanical components. The spectrometerââ?¬â?¢s optics chamber can be used with gratings\noperated in either inside or outside orders, and the detector assembly can be reconfigured accordingly.\nThe spectrometer can be designed to have high spectral resolution, exceeding 10 000 resolving\npower when using small source (âË?¼1 Ã?¼m) and detector pixels (âË?¼5 Ã?¼m) with high line density gratings\n(âË?¼3000 lines/mm), or high throughput at moderate resolution.We report two such spectrometers with\nslightly different design goals and optical parameters in this paper.We show that the spectrometer with\nhigh throughput and large energy window is particularly useful for studying the sustainable energy\nmaterials. We demonstrate that the extensive resonant inelastic X-ray scattering (RIXS) map of battery\ncathode material LiNi1/3Co1/3Mn1/3O2 can be produced in few hours using such a spectrometer.\nUnlike analyzing only a handful of RIXS spectra taken at selected excitation photon energies across the\nelemental absorption edges to determine various spectral features like the localized dd excitations and\nnon-resonant fluorescence emissions, these features can be easily identified in the RIXS maps. Studying\nsuch RIXS maps could reveal novel transition metal redox in battery compounds that are sometimes\nhard to be unambiguously identified in X-ray absorption and emission spectra. We propose that this\nmodular spectrometer design can serve as the platform for further customization to meet specific\nscientific demands....
Charge densities of iso-structural metal hexaborides, a transparent metal LaB6 and a semiconductor\nBaB6, have been determined using the d > 0.22 Ã?â?¦ ultra-high resolution synchrotron radiation X-ray\ndiffraction data by a multipole refinement and a maximum entropy method (MEM). The quality of the\nexperimental charge densities was evaluated by comparison with theoretical charge densities. The\nstrong inter-octahedral and relatively weak intra-octahedral boron-boron bonds were observed in\nthe charge densities. A difference of valence charge densities between LaB6 and BaB6 was calculated\nto reveal a small difference between isostructural metal and semiconductor. The weak electron lobes\ndistributed around the inter B6 octahedral bond were observed in the difference density. We found the\nelectron lobes are the conductive Ãâ?¬-electrons in LaB6 from the comparison with the theoretical valence\ncharge density. We successfully observed a spatial distribution of electrons near the Fermi level from the\nX-ray charge density study of the series of iso-structural solids....
A new methodology able to model and reconstruct the transverse trace space of low-emittance electron\nbeams accelerated in the bubble regime of laser-plasma interaction is presented. The single-shot\nmeasurement of both the electron energy spectrum and the betatron radiation spectrum is shown to\nallow a complete measurement of the transverse emittance, including the correlation term. A novel\ntechnique to directly measure the betatron oscillation amplitude distribution is described and tested at the\nSPARC-LAB test facility through the interaction of the ultrashort ultraintense Ti:Sa laser FLAME with a\nHe gas-jet target. Via the exposed technique the beam transverse profile is also retrieved. From the study of\nthe electron transverse dynamics inside the plasma bubble, the nonlinear correlation between the betatron\namplitude and the divergence, i.e. the angle with respect the acceleration axis, is found. The angular\ndistribution of the electron beam inside the bubble is retrieved. The knowledge of the trace-space density\nallows a more accurate measurement of the transverse emittance with respect to previous paradigms....
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