[Nexus-developers] Some more definitions, NXmeta
Mark Koennecke
Mark.Koennecke at psi.ch
Fri Oct 30 15:14:13 GMT 2009
Freddie,
freddie.akeroyd at stfc.ac.uk wrote:
> Mark,
>
> I know NIMROD has no choppers either - there are probably others too.
> The number you are referring to is the "primary flight path" and is
> stored as a negative distance number in the NXmoderator (this being the
> effective "source" of neutrons). Though you can calculate a reasonable
> "engineering value" for this based on knowing where the target is etc I
> think you may end up calibrating an effective distance or adding in some
> sort of "time delay" factor as it probably isn't so obvious how long
> neutrons are delayed (or their paths lengthened) when moving through the
> moderator
>
> Regards,
>
> Freddie
>
>
OK, if I am not mistaken we agree that this primary flight path is an
important number
and, even if determined from calibration, an instrument constant. IMHO
neither
NXmoderator nor NXchopper are good places to store this, as on some
instruments it
is the moderator (or the synchrotron) and on some the chopper which
determines the
value of this. Do we need a new group for this? May be this is a topic
for our next
telephone conference.
One of the advantages of CIF is that you see many things easily in
ASCII. I missed
that for NeXus and as NXsummary, NXdump were to complicated I wrote a
little
tool in C++ which dumps all the metadata in a NeXus file to screen. I
added some output as
an appendix. You can massage the separators used to make it look even
more like CIF. This
is the second shot below. With this you can grep through your NeXus files...
If people think this is useful, I will put it into contrib/applications.
Best regards and have a nice weekend,
Mark
--------------- Appendices --------------------
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/entry1/title:Nd/Al (Takada) 2.457A T=120Ki
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_entry1_title:Nd/Al (Takada) 2.457A T=120Ki
>
>> -----Original Message-----
>> From: Mark Koennecke [mailto:Mark.Koennecke at psi.ch]
>> Sent: 30 October 2009 07:48
>> To: Akeroyd, Freddie (STFC,RAL,ISIS)
>> Subject: Re: [Nexus-developers] Some more definitions
>>
>> Freddy,
>>
>> freddie.akeroyd at stfc.ac.uk wrote:
>>
>>> Hi Mark,
>>>
>>>
>>>
>>>
>>>> -- I am missing something important: IMHO each TOF instrument has a
>>>> pulse defining chopper. This is the
>>>> chopper, which sends the signal to start counting
>>>>
> time-of-flight.
>
>>>> There may be tons more choppers but they
>>>> are only there to have the neutron packet win the Miss Neutron
>>>> Pulse
>>>> Beauty competition. From what I know,
>>>> the distance of the pulse defining chopper to the sample is very
>>>> important in order to calculate the total flight
>>>> length of the neutron for DA. Now, no chopper was in the tofraw
>>>>
>> on
>>
>>>> the wiki. I think I have to add this. Any
>>>> opinions?
>>>>
>>>>
>>> We have TOF instruments with no choppers at ISIS, the SXD instrument
>>> being an example - they get their timing signal from the synchrotron
>>> extraction pulse. Thus a chopper should be optional in TOFRAW. A
>>>
>> chopper
>>
>>> will, however, always be present on a TOF instrument at a reactor
>>> source.
>>>
>>>
>>>
>> Well, is SXD an exception? I remember there being lots of choppers at
>> ISIS.
>> Anyway, perhaps the chopper is the wrong question then, the data item
>>
> I
>
>> miss is
>> something like the pre_sample_flight_path which is the distance
>>
> between
>
>> the
>> sample and whatever triggers the start of counting time-of-flight. Be
>> it
>> a chopper
>> or a synchrotron. I am next to sure that this is some magic parameter
>> even in the
>> SXD analysis SW.
>>
>> Mark
>>
>>
>>
>>
>>> Regards,
>>>
>>> Freddie
>>>
>>>
>>>
>>>
>>>
>
>
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