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

Technical Report · Mon Jan 01 04:00:00 EST 1990

DOI:https://doi.org/10.2172/7023743· OSTI ID:7023743

Silver, J D; Chantler, C T ^[1]

---

1. Oxford Univ. (UK). Clarendon Lab.

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 >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. This report addresses a set of improvements to the bending techniques for both soft and stiff crystals. 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. 14 figs.

• Research Organization: Lawrence Livermore National Lab., CA (USA); Oxford Univ. (UK). Clarendon Lab.
• Sponsoring Organization: DOE/DP
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 7023743
• Report Number(s): UCRL-21296; ON: DE90009528
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360601 -- Other Materials-- Preparation & Manufacture
440100 -- Radiation Instrumentation
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
640302* -- Atomic
Molecular & Chemical Physics-- Atomic & Molecular Properties & Theory
74 ATOMIC AND MOLECULAR PHYSICS
BENDING
BRAGG REFLECTION
CRYSTAL STRUCTURE
CRYSTALS
DEFECTS
DESIGN
DOCUMENT TYPES
FEEDBACK
IMPLEMENTATION
INTERFEROMETERS
MEASURING INSTRUMENTS
MEASURING METHODS
MICROSTRUCTURE
OPTICAL SYSTEMS
OPTIMIZATION
PERFORMANCE TESTING
PROGRESS REPORT
REFLECTION
SPECTROMETERS
SURFACE PROPERTIES
TARGETS
TEMPERATURE EFFECTS
TESTING
X-RAY SPECTROMETERS