Gerard, Negative extinction is not physical - so has no meaning. There is some other systematic effect that is affecting your result. BTW, I have recently used the x-ray version of extinction in GSAS as well as the neutron (TOF) one on the same set of samples. Both do work and both give about the same level of intensity correction (see the 132 column listing in REFLIST to see these). However, the analysis was a simultaneous refinement using data from a suite of samples with distrete particle sizes (25,20,15,10,& 5 micron Si). Refinements on single data sets gave spurious extinction coefficients, odd absorption coefficients and weird thermal parameters. Maybe you are trying the impossible? Bob Von Dreele
________________________________ From: Gerard, Garcia S [mailto:[EMAIL PROTECTED] Sent: Mon 4/18/2005 5:44 AM To: [email protected]; [EMAIL PROTECTED] Dear all, Just a simple question about GSAS refinement: What physical meaning does a negative extinction coefficient have? if it's meaningless then, what's going on? Thaks indeed,
