Running MERGE for GEM Data  

MERGE may be used to combine together data from different detector groups to produce a single composite diffraction pattern.

MERGE now works on GEM data. (as of 12-7-00)

MERGE is run from GENIE by typing @g_f:merge (NOT from the a_b batch menu).

Q-limits

For the MERGE process the user must specify whether each detector group is to be used in the calculation. For those detector groups which are to be used, the user must also specify the minimum and maximum Q-values to be used for calculating the merged result.

(This is different to the approach taken in the analysis of SANDALS data, where the user specifies a wavelength-range to be used for all detector groups, and is the same as has been used for LAD data. The SANDALS/wavelength-range approach has not been adopted for GEM data because GEM covers a much wider range in scattering angle than SANDALS. However, it is possible to merge GEM data by specifying a wavelength-range - this may be done by typing @g_f:makelim in GENIE or by typing run g_f:makelim outside GENIE, before running MERGE, so as to automatically generate a limits file.)

This Q-limit information may be entered in two different ways:

  1. The parameters may be typed in at the keyboard.
  2. The parameters may be put in a limits file before running MERGE. This method is to be preferred because it reduces problems with typing mistakes, and it means that a permanent record is kept of the parameters used in the data analysis. Details of how to prepare a limits file are given here.

Weighting scheme

When GEM data are merged, they are weighted according to 1/error2. This is the same weighting scheme as is used for SANDALS data, whereas LAD data have been weighted according to the flux, as measured by the vanadium run.

Last updated on 08 Apr 2002 by Alex Hannon (a.c.hannon@rl.ac.uk)