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Proposal to disallow SU from _diffrn_refln_counts_* data names

  • To: Distribution list of the IUCr COMCIFS Core Dictionary Maintenance Group<coredmg@iucr.org>
  • Subject: Proposal to disallow SU from _diffrn_refln_counts_* data names
  • From: James H via coreDMG <coredmg@iucr.org>
  • Date: Mon, 15 Nov 2021 14:50:52 +1100
  • Cc: James H <jamesrhester@gmail.com>
Dear Core DMG,

During the course of recent discussions (see https://www.iucr.org/__data/iucr/lists/ddlm-group/msg01704.html and citations within) it was noted that the _diffrn_refln_counts_* data names are used both to report a measured value (and thus exact, with no SU) and an estimate of the true count rate (a real number with SU). As a refresher, these data names were intended to record the raw measured counts for background and peak using a point detector. None of these data names appear in the COD or wwPDB, and in general have been rendered almost obsolete by the advent of area detectors.

I propose subtly changing the definition for these data names to remove the expectation that a SU could be attached to them. In this I am following the lead of the powder dictionary, which separated the two meanings by introducing equivalent real-valued "intensity" data names with associated SU, and for the "count" data names stated that:
      Standard uncertainties should not be quoted for these values.
      If the standard uncertainties differ from the square root of
      the number of counts, _pd_meas.intensity_* should be used.

Essentially, I propose adding a similar paragraph to the definitions for _diffrn_refln_counts_*. In our case, _diffrn_refln.intensity_net performs the role of intensity and would not be affected by this change.

A related longer-term project that any of you are most welcome to take up is to define data names that would be useful in capturing how peaks are extracted from area detector images.

Please comment. If comments are generally supportive, or absent, the details of this change will be worked out in the Github repository (https://github.com/COMCIFS/cif_core) which you are all welcome to follow and contribute to, of course.

best wishes,

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