>What is left is small fry and we will gladly leave it to x-rays, since
>we are so much better at virtually everything else.
Sorry for the half-serious joke. I really appreciate and use x-rays, but I
cannot avoid thinking that synchrotron x-rays are often used in powder
diffraction for their "extrinsic" qualities (resolution and, for some
machines, signal-to-noise) rather than their "intrinsic" ones (e.g.,
contrast variation). However, powder diffraction is a self-limited
technique in many respects. For instance, it does not make much sense to
have resolutions better than 5*10-4, because there are virtually no samples
as good as that. Neutron powder diffractometers at 3rd generation sources
(like the SNS, ESS and the new japanese facility) will reach those limits.
Finally, we will be able to use each radiation for its intrinsic merits. As
explained by Bill David, drug structure solution is an area where x-rays are
intrinsically better and will always be. In most other areas of powder
diffraction, neutrons have really proven themselves superior, mainly because
of better precision and reduced systematic errors. This is not only true
for mixtures of light and heavy elements. Will the situation change in the
future? I'm not so sure, but I invite comments. On the other hand, the
'unique' x-ray applications (like anomalous diffraction and DAFS) have not
really taken off much beyond demonstration experiments, have they? How long
do we have to wait?
> So, I am happy for both radiations success and performances.
Yes, yes. Let's love each other and be happy talking about
'complementarity', this Arabian Phoenix. 'Complementarity' ignores the fact
that there is a large region of actual or potential overlap where
competition is or could be keen. And competition is always good to improve
performances (look at F1 racing, for example), and get rid of those
'extrinsic' limitations.
Paolo
