[NeXus-committee] Discussion updates, NXsample, NXbeam

[Ron Ghosh]

Comments on NXsample
http://www.neutron.anl.gov:8080/NeXus/10
http://www.nexus.anl.gov/classes/NXsample.html

Garry McIntyre has offered the following comments on
Busing and Levy, which, in the cited paper, is specific 
to a single detector instrument.

He suggests:

   <sample_orientation type="NX_FLOAT[3]" units="degree">
{Eulerian angles omega, chi and phi in th Busing and Levy
convention from Acta.Crysta v22, p457 (1967) but with omega as
the angle to the primary beam, and all angles
right-handed}?</sample_orientation>
 

<orientation_matrix type="NX_FLOAT[n_comp,3,3]">
{Orientation matrix of single crystal sample}{This is the 
UB matrix using the Busing-Levy convention}?</orientation_matrix>

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Comments on NXbeam
http://www.neutron.anl.gov:8080/NeXus/23
http://www.nexus.anl.gov/classes/NXbeam.html

delete "Otherwise....transfer polarisations"
(in the new descriptions the terms initial and final are absent) 


The scalar averages represent a simple summary of the beam status.
I would like to see these optionally complemented by an intensity
profile 
in the 2 directions perpendicular to the beam for the same items. 
 This would allow better corrections for large non-slab samples, 
for example.  A coarse mesh and interpolation could serve to improve the 
corrections, rather than today's assumption of homgeneous beams in
intensity and wavelength distribution etc. 
Often during commissioning such scans of beam profiles are obtained. 

The simulators have proposed their most general solution would be a 
list of  simulated neutrons with information on (say)
x,y,z, vx,vy,vz, t, sx,sy,sz and p, 
respectively positions, velocities, time of flight, spin, and
flux intensity.  (McStas, Vitesse a little different,
NISP another variant)  This would enable any correlation to be studied
with subsequent analysis. 

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I wish all a very Happy Christmas, and consensus in the New Year.

Ron Ghosh

PS I would be grateful to receive news of the availability of an
up to date prototype HDF5 NeXus file which could help in guiding our
local attempts to program NeXus raw data.


-- 
Ron Ghosh, Institut Laue Langevin
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