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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 
definition...

data_diffrn_radiation_probe
    _name                      '_diffrn_radiation_probe'
    _category                    diffrn_radiation
    _type                        char
    _list                        both
    _list_reference            '_diffrn_radiation_wavelength_id'
    loop_ _enumeration           x-ray
                                 neutron
                                 electron
                                 gamma
    _definition
;             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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