[Nexus-developers] NeXus @ TOF

Mark Koennecke Mark.Koennecke at psi.ch
Wed Feb 3 13:11:16 GMT 2010


this is a followup to one of our discussions on one of our teleconferences.

The problem:

At time-of-flight instruments the flightpath length before the sample 
position  is a
number of crucial importance. The trouble is that at some instruments 
this flightpath
starts with a pulse defining chopper, at others it is determined by the 
pulse frequency
of the source or by the moderator. Thus we cannot clearly store it in a 
well defined
group. Creating a special group for this morsel of data is overkill as 
there is no other
data to go with it.

Thus I prose to add  a data field to NXinstrument with a name of 
pre_sample_flightpath  and
a documentation saying:

  This is the distance between the sample and  whatever beam line 
component triggers the
  zero of time-of-flight. This can be a chopper, a moderator or even the 
source. If a suitable
  distance is available in a sub group of NXinstrument, this field ought 
to be a link to this
  distance. Example: if the zero of TOF is determined by a chopper, then 
  is a link to NXchopper/distance.  The usual NeXus rules apply, i.e. 
this is usually a negative
  number in millimeter.

Given the way we work, I will assume that I can make the necessary 
changes to NXinstrument
and start tackling application definitions for TOF at my leisure if I 
did  not get e-mails of protest
or outrage before Friday.

Best Regards,

          Mark Koennecke

P.S. I am invited to give a talk on NeXus at FRM-2 in Munich, February, 18.

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