Difference between revisions of "CHESS X-ray measurements 11/2006"

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In November, we had a one week beamtime at CHESS in Cornell University. We measured rocking curve for several diamond crystal there. Some interesting results are shown as follow.  
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In November, 2006 we had a one week beam time at CHESS in Cornell University. Participating in this run were: CHESS staff scientist Ken Finkelstein and GlueX collaborators Guangliang Yang, Richard Jones, and Franz Klein.  We measured rocking curves for several diamond crystals there. Franz brought with him the target ladder from Hall B, so we had quite a rich variety of samples to examine.
  
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A contour map of rocking curve width for the 20 micron thick diamond crystal (diffraction plane: (-2 2 0)): [[Image:Rockingwidth-414.jpg]].
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* HallB-G50 : type IA natural diamond, said to be 53 microns thick, mounted on the Hall B target ladder.  Experimenters from g8 call this diamond "good", hence the name G50.
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* HallB-B50 : type IIA natural diamond, said to be 40 microns thick, mounted on the Hall B target ladder.  Experimenters from g8 call this diamond "bad", hence the name B50.
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* HallB-20 : type IB synthetic (HPHT) diamond, said to be 18 microns thick, mounted on the Hall B target ladder.
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* twin-50 : type IA natural diamond, said to be 50 microns thick, thought to be a twin crystal, part of the Glasgow collection.
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* badboy-50 : type IIA natural diamond, said to be 50 microns thick, thought to have a large rocking curve width, part of the Glasgow collection.
  
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A rocking curve width map for the 20 micron crystal (Diffraction plane :( 2 2 0)):  [[Image:Rocking_width-405.jpg]].
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All data were archived at UConn.  Some interesting results for the 20 micron crystal are shown below.  
  
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Rocking curves for isolated pixels of the CCD camera used at some interesting locations.
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* [[Results for the 20 micron diamond]]
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[[Image:rocking curve01.jpg]].
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[[Image:rocking curve02.jpg]].
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[[Image:rocking curve03.jpg]].
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[[Image:rocking curve04.jpg]].
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The minimum measured rocking curve width for the 20 micron diamond is around 30 \micron r. The measured rocking curve width is broader than the true rocking curve with of the diamond crystal due to the instrumental broadening. The main source of the instrumental broadening is the x ray beam divergence. For an isolated pixel, the beam divergence is ~ 15 micro radians. We used a (+,-) crystal set-up for the monochromator crystal and the diamond crystal. Since the diffraction angles are different, this setting is not truly non dispersive. The additional rocking curve width from dispersion is ~ 9 micro radians. Taking the above 2 contributions into account, the diamond rocking curve width should be less than ~24 micro radians. Another possible reason for the rocking curve broadening is the curvature of the diamond crystal. The adhesives used for mounting and the marks on the crystal surfaces are the possible sources that could introduce stress to the crystal and the crystal are deformed by stress. If the crystal diffraction plane is all the same at different crystal locations, the measured rocking curve should have the same rocking curve peak position (if the d spacing is all the same for different positions). The rocking curve peak positions recorded by different pixels of the camera are quiet different, this means the 20 micron diamond crystal is severally deformed by stress.
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The following are 2 graphs showing the rocking curve peak positions varying with pixel positions.
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[[Image:peak01.jpg]].
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[[Image:peak02.jpg]].
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Latest revision as of 12:11, 29 November 2011

In November, 2006 we had a one week beam time at CHESS in Cornell University. Participating in this run were: CHESS staff scientist Ken Finkelstein and GlueX collaborators Guangliang Yang, Richard Jones, and Franz Klein. We measured rocking curves for several diamond crystals there. Franz brought with him the target ladder from Hall B, so we had quite a rich variety of samples to examine.

  • HallB-G50 : type IA natural diamond, said to be 53 microns thick, mounted on the Hall B target ladder. Experimenters from g8 call this diamond "good", hence the name G50.
  • HallB-B50 : type IIA natural diamond, said to be 40 microns thick, mounted on the Hall B target ladder. Experimenters from g8 call this diamond "bad", hence the name B50.
  • HallB-20 : type IB synthetic (HPHT) diamond, said to be 18 microns thick, mounted on the Hall B target ladder.
  • twin-50 : type IA natural diamond, said to be 50 microns thick, thought to be a twin crystal, part of the Glasgow collection.
  • badboy-50 : type IIA natural diamond, said to be 50 microns thick, thought to have a large rocking curve width, part of the Glasgow collection.

All data were archived at UConn. Some interesting results for the 20 micron crystal are shown below.

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