Summary : ILL-D2B

armel at armel at
Thu Sep 7 16:01:55 CDT 1995

  About questions on ILL-D2B (see below), all responses were obtained
from Emmanuelle SUARD, local contact at ILL :

From:   SMTP%"suard at"  7-SEP-1995 11:53:06.60

There is a new alternative for the use of D2B. We have very recently 
installed a slit after the monochromator which allows us to have a better 
resolution than before (even better than with the former "high resolution 
mode"). We can control the size of the slit in order to have the best 
compromise between the acquisition time and the resolution according to the 
wishes of the user. Without the slit a diagram at 1.6A takes 2 or 3 hours 
(depending on the sample size). With a very small slit aperture, the time 
could be about 8 hours (same remarks).
It is also possible to work at 2.4A with the same method, the beam lost for 
this wavelenght is very small compared to 1.6A (about 20%). We have also 
installed a new graphite filter, and there is absolutely no contamination of 
any order at 2.4. 
This is an example of U,V,W at 1.6A without any slit (high intensity mode):
0.111  -0.199  0.274
The resolution and the width of the peaks is noticeably lowered by the use 
of the slit.

In the high intensity mode the Rp (background subtracted) could be about 
10%, and it could be improve with the slit (i.e. < 10 %).

These results are very recent as the graphite filter and the slits were 
installed during the last shutdown in august and we are still testing all 
the possibilities.

A new monochromator will be installed on D2B in october which should allow 
us to get an even better resolution.

I can also give you the u,v,w for a diagram of Si taken at 2.4A with a 1cm 
aperture slit (5 hours of acquisition):
0.0588 -0.077 0.078

The original questions :

>Can somebody indicate one or several publications showing
>experimental results from the use of the ILL D2B instrument
>working in the high resolution mode ?
>Alternatively, can somebody answer to the following questions 
>that have no response into the "ILL Yellow Book" :
> -  2 hours in high intensity mode or 20 hours in high resolution
>    mode to have a "good" pattern at 1.594 A, is that correct for
>    an optimal sample ?
> -  what is today the minimal FWHM in high resolution mode 
>    and the one in high intensity mode (or better, the U,V,Ws and
>    profile shapes)?
> -  are the fits very satisfying by the Rietveld method in high
>    resolution mode (at least Rp<10%, background subtracted) ?

          Armel Le Bail  -    armel at

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