Current Issue : January - March Volume : 2015 Issue Number : 1 Articles : 4 Articles
In this paper, several schemes of soft X-ray and hard X-ray free electron lasers\n(XFEL) and their progress are reviewed. Self-amplified spontaneous emission (SASE)\nschemes, the high gain harmonic generation (HGHG) scheme and various enhancement\nschemes through seeding and beam manipulations are discussed, especially in view of the\ngeneration of attosecond X-ray pulses. Our recent work on the generation of attosecond\nhard X-ray pulses is also discussed. In our study, the enhanced SASE scheme is utilized,\nusing electron beam parameters of an XFEL under construction at Pohang Accelerator\nLaboratory (PAL). Laser, chicane and electron beam parameters are optimized to generate\nan isolated attosecond hard X-ray pulse at 0.1 nm (12.4 keV). The simulations show that\nthe manipulation of electron energy beam profile may lead to the generation of an isolated\nattosecond hard X-ray of 150 attosecond pulse at 0.1 nm....
The paper presents a set of tests carried out in order to evaluate the design\ncharacteristics and the operating performance of a set of six X-ray extrinsic optical fiber\nsensors. The extrinsic sensor we developed is intended to be used as a low energy X-ray\ndetector for monitoring radiation levels in radiotherapy, industrial applications and\nfor personnel dosimetry. The reproducibility of the manufacturing process and the\ncharacteristics of the sensors were assessed. The sensors dynamic range, linearity,\nsensitivity, and reproducibility are evaluated through radioluminescence measurements,\nX-ray fluorescence and X-ray imaging investigations. Their response to the operating\nconditions of the excitation source was estimated. The effect of the sensors design and\nimplementation, on the collecting efficiency of the radioluminescence signal was\nmeasured. The study indicated that the sensors are efficient only in the first 5 mm of the\ntip, and that a reflective coating can improve their response. Additional tests were done to\ninvestigate the concentricity of the sensors tip against the core of the optical fiber guiding\nthe optical signal. The influence of the active material concentration on the sensor response\nto X-ray was studied. The tests were carried out by measuring the radioluminescence signal\nwith an optical fiber spectrometer and with a Multi-Pixel Photon Counter....
Serial crystallography using X-ray free-electron lasers enables the collection of\ntens of thousands of measurements from an equal number of individual crystals,\neach of which can be smaller than 1 mmin size. This manuscript describes\nan alternativeway of handling diffraction data recorded by serial femtosecond\ncrystallography, by mapping the diffracted intensities into three-dimensional\nreciprocal space rather than integrating each image in two dimensions as in the\nclassical approach. We call this procedure ââ?¬Ë?three-dimensional mergingââ?¬â?¢. This\nprocedure retains information about asymmetry in Bragg peaks and diffracted\nintensities between Bragg spots. This intensity distribution can be used to\nextract reflection intensities for structure determination and opens up novel\navenues for post-refinement, while observed intensity between Bragg peaks\nand peak asymmetry are of potential use in novel direct phasing strategies....
X-Ray sources, detectors and optical components are now used in a wide range of applications.\nWhat is crucial is the absolute calibration of such devices to permit a quantitative assessment of\nthe system under study. A new X-ray laboratory has been built in Frascati (ENEA) to develop diagnostics\nfor nuclear fusion experiments and study applications of these X-ray techniques in other\ndomains, like new material science, non destructive tests and so on. An in-house developed selfconsistent\ncalibration procedure is described that permits the absolute calibration of sources\n(X-ray emitted fluxes) and detectors (detection efficiencies) as function of the X-ray photon energy,\nin the range 2 - 120 keV. The calibration procedure involves the use of an in-house developed code\nthat also predicts the spectral response of any detector in any experimental condition that can be\nsetup in the laboratory. The procedure has been then applied for the calibration and characterisation\nof gas and solid state imaging detectors, such as Medipix-2, GEM gas detector, CCD camera,\nCd-Te C-MOS imager, demonstrating the versatility of the method developed here....
Loading....