At 11:33 24/09/99 +0100, Kenneth wrote:
>As ever, none of Armel's replies actually acknowledge
>the validity of their resolution arguments....
So, I want to acknowledge Brian Toby who pointed
that the best minimal FWHM for a neutron powder
diffractometer at constant wavelength was 0.12° (2-theta)
rather than the 0.10° which I suggested.
ToF users do not like FWHM in degrees, I may
understand that. Anyway, each time I record a powder
pattern, I have a look to this crucial value for those who
are performing SDPDs, and (delta d)/d is not my cup of
tea when looking at a profile shape.
You may know that St Armel was a disciple of St Thomas,
so that, I am really impressed by the ToF HRPD 0.006 degrees
given by Bill :
>
> Now (delta d)/d = (delta theta)* cot(theta). Putting 2 theta = 90 and
> cot(theta)=1 then
> (delta 2 theta) = 10-3 radians = 0.06 degrees ( at 90
> degrees equivalent)
> and !! ...
> (delta 2 theta) = 10-3 radians = 0.006 degrees ( at 11
> degrees equivalent)
> and essentially linear in between.
However, I just would like to touch with my fingers such
a wonderful powder pattern. Can you give me a Web or FTP
address where I could download the best example ?
>Coincidentally, I have an experiment starting on HRPD
>tomorrow. It's a structure determination - wish me luck ??
Sure, good luck ! With (delta 2 theta) = 10-3 radians, it should
be feasible.
Best,
Armel
