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Re: Neutron diffraction experiments

  • To: Multiple recipients of list <coredmg@iucr.org>
  • Subject: Re: Neutron diffraction experiments
  • From: syd@crystal.uwa.edu.au (Sydney R Hall)
  • Date: Tue, 17 Feb 1998 13:44:58 GMT
This would not be the first neutron study to appear in Section C so
presumably other authors were not so squeamish about using the existing
data items in the cif submission.  Nevertheless, these data items were 
intended for x-ray studies, so possibly new items are needed for neutron
and electron diffraction studies. One should note however that the 

    _name                      '_diffrn_radiation_probe'
    _category                    diffrn_radiation
    _type                        char
    _list                        both
    _list_reference            '_diffrn_radiation_wavelength_id'
    loop_ _enumeration           x-ray
;             Name of the type of radiation used. It is strongly encouraged
              that this field be specified so that the probe radiation
              can be simply determined.

identifies the radiation type, so that the possibility also exists for 
making the units of _refine_diff_density_min and _max implicit.... though
this could prove messy if one was searching a cif archive just on these
items. Its highly likely that other definitions would be needed as well...
noting that all of the _refln_F_* items are defined in electrons at the 
moment. And of course with the increasing use of electron diffraction there
will be a need for structure factor coefficients etc. in Volts as well.

My inclination would be use the existing definitions in a generic fashion
with the units linked to the radiation employed... its simpler and would
avoid the triplication (more perhaps) of all radiation-dependent items. 
On the other hand my point of view is more that of an author and user
rather than an archivalist... and readily admit that from a publisher's 
point of view the assignment of units to generic data items is not as 
straightforward as is possible with explicit definitions.

Cheers, Syd.

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