ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
Measurement of very small differences of the total cross section is the current demand for the spectrometers dedicated to time-dependent experiments carried out under various time-ramped parameters. The dispersive optics and more precisely the full x-ray-absorption spectrometer is mechanically movement-free during data collection which can last over 12 h at LURE-DCI to be sensitive to relative change of the absorption of the order of 10−5. In this range, artefacts due to the drift of silicon lattice spacing under temperature change of the crystal, and drifts of the detector position because of liquid–nitrogen evaporation contained in the cryostat, are sources of errors which have been identified and cured or ... by-passed. The accuracy in difference measurements is now of the order of 10−5 for a total cross section measured equal to 1. In term of optics stability a difference signal of 10−4 out of 1 can be generated by an absorption edge shift caused by a 0.05 K drift of the temperature of the silicon crystal at 7 keV. These performances are essential for the measurement of XMCD in the hard-x-ray range. Water cooling of the dynamically bent crystal reduces dramatically the change of the Si temperature. Adequate geometry makes the spatial drift of the position of the photodiode array much less concerning. The focusing efficiency is also a key parameter to push high-pressure x-ray-absorption spectroscopy (55 GPa), and high-temperature XAS (2000 K), and the combination (15 GPa, 800 K). Simple devices, taking advantage of the focusing geometry, have been successfully tested these last two years. © 1995 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1145859
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