From:   SMTP%"dipo@shaw.ca" 20-NOV-2002 20:02:18.59
To:     cockcroft@img.cryst.bbk.ac.uk
CC:
Subj:   PD02 Questions

Hello Jeremy,

I noticed some minor typos in Release 3.  They are mainly aesthetic and do not 
prevent an understanding of the material.  

Title: Inside the sealed glass x-ray tube.  Line 5: "Chilled water (at 
approximately 15°C) is sprayed at high pressure (approximately 4 bars) though 
(THROUGH) the slit onto the back of the anode surface".

mm appeared as mn;m almost everywhere in Release 3.

Title: Mirrors - Functions: Figure caption - "Note that the 
refraction/diffraction angle is shown slightly exaggerated for clarity".  
Shouldn't refraction angle be reflection angle since the Figure shows 
diverging incident beam and total internal reflected parallel beam?

Title: Reflection geometry - paragragh 4 line 1: "The tube is aligned so that 
the beam divergent on the sample is at angle χ to the anode surface".  The 
divergence angle in the Figure is labelled xi not chi.

Title: Data acquisition - line 1 after the 3 figures while for A the course 
step size of 0.05°.  "A" should be "B" and "course" should be "coarse".

I also have a few questions in Release 3.

1 - Inside the sealed glass x-ray tube, you wrote "One end of the filament is 
at the same potential as the focussing cup (e.g. -40 kV) while the other end 
is slightly more negative, thus providing a current of a few amps to heat the 
filament".  Could you please explain this further? My thinking is that the 
focussing cup is at a more negative potential than the filament to generate 
equipotential fields necessary for focussing the electrons on the anode and 
that a variable bias resistor connected to the filament power supply provides 
a self biasing electrode.

2 - In practice, is the pulse height discriminator attached to a scintillation 
detector enough to remove sample flourescence?  I appreciate that the 
discriminator cannot resolve Ka and Kb.

3 - Under the title reflection geometry (and transmission geometry), you refer 
to the dotted lines as the focussing circle.  Is this a generic name?  
My understanding is that the dotted line is the goniometer circle with a 
constant radius (sample at the origin) whereas the sample, source and receiving 
slit are "on" the focussing circle with a variable radius. Same as the 
monochromator focussing circle.

4 - Sample holders:  Do manufacturers typically specify the divergent slit 
size to be used for certain holders in order to compensate for beam spill at 
low angles?
    
Best regards,

Dipo

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