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UB Matrix for Triple Axis Instruments
WARNING: this formalism allows to drive out of the scattering plane using tilt thereby possibly destroying your cryostat. See below tasub outofplane command
> CELL a b c alpha beta gamma
set unit cell constants. If b or c are omitted, the same value as
for a is used, if angles are omitted, they are set to 90 degress.
Without arguments, the cell constants are listed.
> REF qh qk ql a4 a3 sgl sgu ki kf
Make an entry in the list of peaks. For angles and k-values not given,
the current motor positions are used. If the given
qhkl triple already exists, its list entry is overwritten.
If not, a new entry is made.
The peak number and the peak data are returned.
> REF CLEAR peak
Remove a peak.
> REF CLEAR ALL
Remove all peaks.
> REF
List all peaks.
> MAKEUB peak1 peak2
Calculate, activate and print out the UB matrix, as well as the
peak list with qhkl values calculated back. peak1 is used
as the main peak, i.e. driving to the angles given for this peak
will correspond to a QHKL which may only differ by a scalar factor
of about one, if the cell constants are not correct. peak2 is
used only for determining the scattering plane.
It has to be checked that this is fully compatible with the
TASMAD specification. In principle, AX,AY,AZ should correspond
to peak1 and BX,BY,BZ to peak2.
Markus Zolliker: there should be a an easy way helping
the user to correct the cell constants (for example due to
thermal contraction) according to the measured peak.
> LISTUB
List the UB matrix, the cell constants and all stored reflections.
> TASUB OUTOFPLANE 1
This formalism allows to drive out of the scattering plane using the tilt motors of the sample stage. Some cryostats cannot stand this.
Therefore driving out of plane can be switched off and on. This command switches out of plane operation on.
> TASUB OUTOFPLANE 0
This formalism allows to drive out of the scattering plane using the tilt motors of the sample stage. Some cryostats cannot stand this.
Therefore driving out of plane can be switched off and on. This command switches out of plane operation off.
> TASUB OUTOFPLANE
lists the current value of the outofplane variable
Example session:
(Some numbers might not be correct, as this module
does not yet work in this form).
We enter cell values
> CELL 2.88 2.88 2.88 90 90 90
Find the peak 2 0 0 and optimize it
...
Once we are at the maximum:
> REF 2 0 0
Peak QH QK QL A4 A3 SGL SGU
1 2.00 0.00 0.00 65.31 -87.21 1.25 -5.22
Find the peak 0 4 4 and optimize it.
...
Once we are at its maximum:
> REF 0 4 4
Peak QH QK QL A4 A3 SGL SGU
1 0.00 4.00 4.00 65.31 -87.21 1.25 -5.22
Show again the peak list:
> REF
Peak QH QK QL A4 A3 SGL SGU
1 2.00 0.00 0.00 65.31 -87.21 1.25 -5.22
2 0.00 4.00 4.00 99.45 20.39 4.25 -1.22
Calculate the UB matrix, with 2 0 0 as primary peak and 0 4 4 as
secondary peak.
> MAKEUB 1 2
UB 2.456 0.530 -0.200
-0.530 2.456 -0.090
0.200 0.090 2.456
Peak QH QK QL A4 A3 SGL SGU QH QK QL
1 A 2.00 0.00 0.00 65.31 -87.21 1.25 -5.22 2.03 0.00 0.00
2 B 0.00 4.00 4.00 99.45 20.39 4.25 -1.22 0.02 3.95 4.03
the last 3 columns above show the Q values calculated back from the angles.
We drive now to the 2 0 0 peak
> DR QH 2 0 0
> PR A4 A3 SGL SGU
A4 = 64.218
A3 = -87.515
SGL = 2.258
SGU = -3.217
The value of A4 has changed, because the cell constants do not match the values
given for the first peak. The value of A3 has changed by the same reason, and
in addition, because the the plane given by 2 0 0 and 0 4 4 is now tilted back
into in the scattering plane. For the latter reason SGU and SGL have changed also.
> DR QH 3 3 3
> PR A4 A3 SGL SGU
A4 = 82.516
A3 = -31.215
SGL = 2.258
SGU = -3.217
note that the values for SGU and SGU have not changed. The will not change
as long as we stay in the scattering plane (no drives to Q3) and as long
as the UB matrix has not changhed.
> REF 3 3 3
Peak QH QK QL A4 A3 SGL SGU
3 3.00 3.00 3.00 82.32 -31.25 2.26 -3.22
> MAKEUB C B
UB 2.456 0.530 -0.200
-0.530 2.456 -0.090
0.200 0.090 2.456
Peak QH QK QL A4 A3 SGL SGU QH QK QL
1 2.00 0.00 0.00 65.31 -87.21 1.25 -5.22 2.03 0.00 0.00
2 B 0.00 4.00 4.00 99.45 20.39 4.25 -1.22 0.02 3.95 4.03
3 A 3.00 3.00 3.00 82.32 -31.25 2.26 -3.22 3.00 3.00 3.00
We have calculated a new UB matrix, based on the peak 3 3 3 as primary and the
0 4 4 as secondary peak. The UB matrix has not changed, as we were already exactly
at 3 3 3.
This particular version was published on 09-Mar-2006 11:16:00 UTC by 129.129.194.220.
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