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Improved crystal bending techniques applied to the LLNL dual-arm Johann mounting x ray spectrometer (Final Report)

Silver, J D ; Chantler, C T

Improved crystal bending techniques applied to the LLNL dual-arm Johann mounting x ray spectrometer (Final Report), 1990

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  • Título:
    Improved crystal bending techniques applied to the LLNL dual-arm Johann mounting x ray spectrometer (Final Report)
  • Autor: Silver, J D ; Chantler, C T
  • É parte de: Improved crystal bending techniques applied to the LLNL dual-arm Johann mounting x ray spectrometer (Final Report), 1990
  • Notas: content type line 59
    SourceType-Reports-1
    ObjectType-Report-1
  • Descrição: Earlier investigations using the LLNL Spectrometer have revealed several limitations to the resolution of observed spectral lines. The first is the broadening due to the finite target source, together with secondary effects due to the bowing of the target. Other limitations relate to the target and spectrometer geometry, and in particular to the small (2R = 30cm) Rowland Circle radius. At small radii the production of a perfect curvature becomes increasingly difficult as distortions of the mosaic spread of crystallite angles are introduced by the stress. This is particularly true of lattice planes with three non-zero Miller indices (e.g., Si111 compared to Si220) and of stiff or thick crystals (e.g., silicon and quartz, which will shatter if greater than 0.2mm crystals are bent to this radius), but small broadening and asymmetrical shifts are also introduced for other crystals. Conversely, soft crystals (such as thin PET) will bend readily to the radius but distort and relax in mountings with fixed bending forces. A set of improvements to the bending techniques for both soft and stiff crystals is addressed. The first and most important development is the use of parallel, vertical posts and (symmetrical) bending points driven by micrometers instead of the earlier formed (i.e., pressed) crystals. The primary advantage is that the curvature from a small number of stress points is calculable, reproducible and does not introduce random stresses and distortions over the surface. The major methods used include the 2-point, 2-bar mount and the 4-point, 4-bar method. Various 4-point, 2-bar methods were also used. (DOE)
  • Idioma: Inglês
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