source: trunk/tutorial3/alumina8.html @ 930

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1<html>
2<head>
3   <title>EXPGUI Alumina Tutorial, part #8</title>
4</head>
5
6<style>
7A:link {text-decoration:none}
8A:vlink {text-decoration:none}
9</style>
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11<BODY BGCOLOR="#FFFFFF"
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14
15<?
16   include("/var/www/include/navigation.inc");
17   include("/var/www/include/utility.inc");
18?>
19<blockquote>
20
21<TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT>
22<TR><TH><A  Href="index.html">Intro</A> 
23</TH><TH><A Href="alumina9.html">Next page</A>
24</TH><TH><A Href="alumina7.html">Previous page</A>
25</TH></TR></TABLE><BR CLEAR=ALL>
26
27
28<CENTER>
29<H1><HR noshade width="75%" size="2" align="center">
30GSAS/EXPGUI Alumina tutorial (part 8)<BR>
31Fitting the Diffractometer Zero Correction
32
33<HR noshade width="75%" size="2" align="center">
34</H1>
35</CENTER>
36<P>
37Now that the unit cell parameters have been fit, it is now
38a good idea to also refine the diffractometer zero correction.
39<P><HR noshade width="50%" size="4" align="center"><P>
40The diffractometer zero correction refinement flag is found on the
41histogram panel, as seen below. Click on the check box for the zero correction
42near the middle of the window to refine the parameter.
43<P><img alt="tutorial screen dump" src="8a.gif" align=RIGHT>
44<BR clear=all>
45<blockquote><I>
46Note that the diffractometer zero correction is refined for parallel beam
47instruments, such as neutron and synchrotron diffractometers. It should
48not be used for Bragg-Brentano instruments
49(laboratory flat-plate parafocussing instruments).
50For Bragg-Brentano instruments, instead the sample displacement parameter
51(shft) should be refined instead.
52When needed, for Bragg-Brentano instruments, the sample transparency correction
53(trns) may also be refined.
54</I></blockquote>
55<P><HR noshade width="50%" size="4" align="center"><P>
56
57When GENLES is run, as shown below, a small but significant improvement is
58seen in the agreement factors.
59<P>
60<img alt="tutorial screen dump" src="8b.gif" align=RIGHT>
61<BR clear=all>
62<P><HR noshade width="50%" size="4" align="center"><P>
63
64Note that the zero correction has refined from the starting value of 0.04
65(0.0004 degrees two-theta) to 1.73 (0.0173 degrees two-theta). This small
66correction is needed to obtain a good fit and accurate lattice parameters.
67<P><img alt="tutorial screen dump" src="8c.gif" align=RIGHT>
68<BR clear=all>
69<P><HR noshade width="50%" size="4" align="center"><P>
70<HR>
71Previous: <A HREF="alumina7.html">
72Fitting the Unit Cell
73</A>
74<BR>
75Next step: <A HREF="alumina9.html">
76Initial Fitting of Profile Parameters
77</A>
78
79<HR>
80</blockquote>
81<P><font size=-1><A HREF="MAILTO:crystal@NIST.gov?subject=WWW page <?=$PHP_SELF?>">Comments, corrections or questions: crystal@NIST.gov</A></font><BR>
82<font size=-1><? lastmod(); ?> 
83<BR>$Revision: 930 $ $Date: 2009-12-04 23:14:35 +0000 (Fri, 04 Dec 2009) $</font>
84</body>
85</html>
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