For question about this experiment and not covered in the following user guide, you can mail d2am.


Overview of the experiment.

The material science diffractometer is a general purpose instrument which was designed to record intensities over a wide dynamical range. It consists of 7 circles allowing users to record data in and out of the polarization plane. The whole instrument lies on a table used for its alignment.

The (x,y,z) axis are defined on Figure 1.

Fig 1 Fig 2

 

  • The sample can be oriented through 3 circles of the instrument :
    1. THETA : sample rotation around a horizontal axis perpendicular to the incident beam (y).
    2. CHI : sample rotation around x, it is carried by THETA. On figure 1 chi=90.
    3. PHI : sample rotation around the sample normal. It is carried by CHI and THETA, so that the sample lies horizontal at chi=90 (its normal is z) and vertical at chi=0 (its normal is then y). Note that at CHI=0, THETA and PHI axis are parallel and horizontal.
  • The detection line uses the 4 remaining circles. 2 of them adjust the position of the detector arm in and out of the diffraction plane. The 2 last are used to set the analyser at the right energy.
    1. ALPHA : horizontal motion of the detector arm to allow measurement out of the polarization plane, its full use needs a special configuration of the experiment control program.
    2. 2THETA ( or tth ) : vertical motion of the detector arm. It is carried by ALPHA.
    3. THETA_A ( or omegaa ) : bragg angle for the analyser cristal, carried by detector arm.
    4. 2THETA_A ( or ttha ) : vertical motion of the detector after the analysing crystal.

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Description of the 7 circles goniometer.

The main characteristics of the 7 axis are listed below, units and angular values are user values expressed in physical values:

motor name in spec angular range (deg.) speed (deg./s) step (deg.) mechanical origin at user angle (deg.)
th -20 +70 0.35 0.0001 6.2337 (6Dec95)
chi -30 +110 0.45 0.0003 -2.452 (6Dec95)
phi continuous 5 0.00025  
alpha -75? +40? 2.5 0.0001 1.0488 (29Jun94)
tth -8 +130 1 0.00005 91.8157 (20Sep95)
omegaa continuous 2.5 0.0001  
ttha   0.5 0.00005 0.0955 (20Sep95)

 

The spec macro get_7csettings can be used to ensure that user and dial values agree, It use the data file 7c_settings.db of your directory or the standard one (~/specadm/d2_macros/7c_settings.db).

You can get a complementary description of motor axis.

Sample environments available :