Re: Meanwhile, back in the lab...

In article <v_5je.95$25.20243@xxxxxxxxxxxxxxxxx>,
<mmeron@xxxxxxxxxxxxxxxxxx> wrote:
>In article <d6i7e3$h7v$1@xxxxxxxxxxxxxxxxxxxxxxxx>,
>glhansen@xxxxxxxxxxxxxxxxxxxxx (Gregory L. Hansen) writes:
>>In article <1116467397.252775.237190@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
>>Sbharris[atsign]ix.netcom.com <sbharris@xxxxxxxxxxxxx> wrote:
>>>Greg, was my last question to you too difficult to answer off hand?
>>>
>>>The question I have is this: what happens when you run "few mev"
>>>protons or neutrons through single crystals of (say) graphite at small
>>>angles in comparison to the plane defined by the sheets of C atoms.
>>>With the beam passing orthogonally (the 001 direction) through the
>>>common plane defined by the stacked sheets, you'd get one attenuation
>>>coeefficient. And presumably at right angles to that, so the particles
>>>were passing straight down the "alleys" between the sheets (the 112
>>>direction) you'd get another coefficient. In both cases these would
>>>related to the average density of the crystal in the direction of
>>>interest. But now, what happens when you tilt the thing just a little
>>>in either direction from 112??? Do the particles now go off greatly to
>>>one side or the other? And is the effective shielding coefficient per
>>>mass a LOT greater in the direction where the particles DON'T go, than
>>>you could get with other materials?
>>>
>>
>>
>>Sorry, I didn't see it before. I search for "hansen", so that's a sure
>>way to catch my attention. Otherwise, whether I read a message or not is
>>more or less by chance.
>>
>>But the angle of incidence still equals the angle of reflection, and that
>>angle is relative to a scattering plane. The Bragg peaks in an ideal
>>crystal are delta functions, any real crystal has peaks of a certain
>>width, the Darwin width(?), that depends on its size and quality.
>
>Oh, no. The Darwin width of a perfect crystal with unlimited size is
>still finite. Imperfections, absorption and other issues may broaden
>it further but even an ideal crystal doesn't give a delta function.

Really? I'll have to check on that, but I thought I remembered Fourier
transforming lattices and finding delta functions in the limit of infinite
crystal size.

--
"Coincidences, in general, are great stumbling blocks in the way of that
class of thinkers who have been educated to know nothing of the theory of
probabilities." -- Edgar Allen Poe
.