RE: global chi2

[TRILLON Gilbert]

maybe you shouldn't substract the background in EVA, as the model used to simulate it is poor. A better way of taking care of the background may to use some polynomial model (for instance) in fullprof, and to refine paramaters of the choosen model. Gilbert TRILLON     -----Message d'origine----- De : eli [mailto:[EMAIL PROTECTED] Envoyé : jeudi 26 août 2004 10:54 À : [EMAIL PROTECTED] Objet : global chi2 Dear Rietvelders I am trying to refine (fullprof) x-ray (Cu Ka) pattern of spinel CuTi2(S,Se)4 which was measured in flat specimen sample holder  in D8 Th:Th without monochromator (10-158 2Th). the experiment details were step each 0.02 2Th with 10 sec per step. the background was subtructed in EVA.  the problem that i am facing is that the R_Bragg is 3.71 but the global chi2 is 7.5 only if i am excluded the region to 10 - 80 2Th. what can be the reason for that?   Thank's in advance for your ideas   Eli