The following paragraph is from "Rietveld Analysis Program BGMN" (copyright 2006 by J bergmann, Dresden). (scanned and recognized by an OR program)
"The advantages of the variable divergence slits are: ; Correct intensity values in the entire angular range because of the sample holder is not irradiated Higher intensity in the case of high angles in comparison to the fixed slit Better grain statistics especially for higher angles Lower angular limit due to prevention of irradiation of sample boundaries Low intensity of the background at low angles Therefore, it is explicitely recommended to use automatic divergence slits in structure refinement and phase analysis." ----- Original Message ----- From: [EMAIL PROTECTED] To: [email protected] Date: Tue, 07 Aug 2007 16:15:59 +0100 Subject: Re: fixed slits or fixed radiated length Bragg-Brentano XRPD > Dear Silvina, > > The purpose of divergence slits is to increase the intensities of > reflections at > high angle, the flip side is an increase in background and peak > broadening (that > will extenuate peak overlap) at high angle. > > For structural work it is best to stay with fixed slits, no > modification needed > for the profile function - though TOPAS (academic) is the only program > to date (I know of) that can model divergence slits. > > Old school techniques of counting for longer at high angle is the best way > to > improve stats and will not unduly effect your profile function. > > Divergence slits are useful for phase identification especially if you are > processing a bulk number of samples. Stick with fixed slits for Rietveld > analysis. > > Regards > > William Bisson > CCP14 administrator > http://www.ccp14.ac.uk > > Quoting Silvina Pagola <[EMAIL PROTECTED]>: > > > Hi, > > I have a question regarding the use of fixed radiated length data in > > a laboratory powder diffractometer, with Bragg-Brentano geometry and > > programmable divergence and antiscatter/receiving slits, which can > > also be used in the "fixed slit" mode (in which the irradiated length > > on the sample varies with the theta angle). > > This is, for what cases the fixed radiated lenght is recommended > > instead of fixed slits data?. > > I have only these two choices for structure solution. For one > > compound I solved, it seems to work better the fixed radiated length > > data, although the background increases at high angles and I have to > > refine absorption (surface roughness), to get positive thermal > > factors. Could someone explain why to use one dataset or the other > > for structure solution and refinement? > > Thanks, > > Silvina. > > > > >
