Re: [ccp4bb]: Re: your mail

["Leonard M. Thomas" <thomasle@its.caltech.edu>]

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I believe the "magic" angle he maybe talking about is from solid state
NMR.  If I recall, from an NMR class in grad school a number of years ago,
the magic spinning angle in solid state NMR is around 56 degrees or so.

Leonard M. Thomas Ph.D. 		Howard Hughes Medical Institute
X-ray Laboratory Manager		Division of Biology, 156-29
thomasle@caltech.edu			California Institute of Technology
626-395-2661 or 3062			Pasadena, CA 91125

On Tue, 11 Dec 2001, Bart Hazes wrote:

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> On Tue, 11 Dec 2001, marius wrote:
>
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> > > Can someone explain to me (in simple words) the pratical
> > > and theoretical usefullness of a diffractometer with kappa
> > > geometry with magic angle (54.? deg) using pre-oriented
> > > and randomly oriented crystals.
> >
> > I have to be more specific:
> > Rotation of the crystal cuts a torus out of reciprocal space.
> > Once one of the reciprocal cell axes is oriented along the rotation
> > axis some reflecions (or their symmetry mates) never pass
> > through the Ewald sphere. Hence, completeness is severly hampered.
>
> Setting a specific kappa angle will not help you for randomly oriented
> crystals as their axis of highest symmetry could still line up with the
> rotation axis. There is also no "magic" angle for cusp data. The needed
> misalignment of the symmetry axis wrt the oscilation axis depends on the
> resolution of the data (it should be more than "theta").
>
> The old Siemens multi-wire detectors came with a 45 degree kappa geometry.
> When mounting a crystal in a vertical position on this system, you could bring
> it into a horizontal orientation by a 90 degree rotation around kappa. The
> 90 degree change in going from vertical to horizontal is optimal to collect
> your cusp (blind region) data. But I don't know where your magic number comes
> from.
>
> Bart
>
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