Represention of a serie of scans during acquisition to survey different regions of the reciprocal space
and identify complex features due to incommensurability or diffuse.
w2=make_volume(w1,/hkl)
Using the program suite described in the TOF-Manual (linked in the FRONT page)
here is an example of diffuse scattering in manganese oxide (MnO) from D7.
Magnetting scattering cross-section of a 5g MnO single cristal at -122°C, 30°C above the temperature at which
the sample orders magnetically. The nuclear contribution to the scattering has been removed using neutron polarisation
analysis. Magnetic manganese atoms tend to align themselves at temp greater that the Néel temperature.
GEORGE (General Experiment Organisation, Response and Guidance Executive) allows on-line data analysis to
be combined with any instrument control and data acquisition sequences. The macros written by the instrument scientist
has a frequency property which determines how often information is sent to, or received from the instrument
control system. Other properties when updated in the macro, allow George to display "live" texts, images, fit results etc...
The Control Pad with there pull-down buttons is dynamicaly constructed at launch from a text file edited by the scientist!!!
This interface allows the noisy or unwanted spectra in a workspace to be masked and the remaining spectra to be regrouped into a new workspace. At start-up a colour chart is displayed until a workspace is loaded using the Load W# button.
The Mask & Group window with some spectra
already masked
The TOF Manual which will help you to reduce Time-of-Flight data is linked to the FRONT page
DidLine |
Convert to Energy (t2e
) |
Rebinning Irregular Data (rbin
) |
Convert to s(Q,w) | Normalise
to Vanadium (vnorm
) | Normalise
Backscattering Spectra (bsnorm
) | Line-up
Elastic Peaks (lineup
)
A friendly way to inspect rapidly the Tof raw data.
The call is :Wi = didline(Wj)
Where Wj = Workspace containing the raw sample.
This command invokes an intermediate interface to specify essentials inputs.
Before calling didline check the following parameters:
Pj( 2)= Doppler frequency (Hz)
Pj(11)= Temperature (K)
Pj(18)= Channel width (microsec.)
Pj(21)= Wavelength (angstroms)
Pj(27)= Distance Det - Sample (meter)
t2e
)LAMP uses the function t2e
(tee) to convert the x axis from
time-of-flight (channels) to energy. Usually it is best to normalise, remove
noisy spectra, subtract background etc. before using this transformation.
The function is written in IDL and can be examined by pressing the
User Macros? button and selecting
t2e.pro
from the list which appears.
w2=t2e(w1)
t2e
exist in the history of the workspace?
t2e
will convert
the energy scale and make the appropriate corrections to the intensity for
changing from time-bins to energy-bins. The title of the x-axis is changed.
A "shot" sound indicates success and a "crunch" sound
signifies an error. Please report unexplained errors.
lineup
to align all positions, or
sum all spectra of interest,w2=total(w1(*,20:80),2)
t2e
.
The sample energy-loss side of the energy spectrum may go to very high
values. If the energy spectrum looks odd, with the elastic-peak at one end,
select a more realistic plot-range.
If you have been using plot limits in channels remember to change these
values before plotting in energy.
rbin
)Data on an irregular energy-scale can be rebinned to a regular grid by
typing
If required this command can be entered directly in the formula-entry window
as, eg. When time-of-flight versus angle data are transformed to energy versus
momentum transfer (Q, Typing Adjust the sliders to select the workspaces (in and out),
the energy (E) and Q ranges of interest. The default maximum Q
corresponds to the maximum energy transfer in the highest-angle spectrum -
that is 1 point! Usually you should reduce the maximum Q value. You should
avoid generating more than about 30 points in energy and 50 values in Q.
Press the Do Interpolation button to start the calculation.
If The function The limits are those of the elastic peak in the vanadium spectra and must
be given in channels not energy. The function Because there are frequently small differences between the distance from
the sample to individual detector-groups there can be slight differences in
the time-of-flight channel in which the elastic peak arises. When keyword NOFIT is set, the function
The counting statistics in an individual spectrum need to be adequate to
enable the elastic-peak to be found. Otherwise the routine does nothing.
rbin
in the
formula-entry window. A window opens in which the energy range and energy
increment can be chosen for a given input and output workspace.
The rbin
window makes and executes the command: w_out=ebin(w_in, E min, E max, increment)
w2=ebin(w1,-0.7,7.0,0.05)
Convert to s(Q,
)
), the data points fall on
a rather irregular grid. A Delaunay triangulation of the planar set of Q,
points is constructed and used to interpolate
the data onto a regular grid which can simplify preliminary analysis.
The function sqw
performs this task but the syntax is
complicated so you are strongly recommended to use the
sqwwin
command, but if you wish to make
conversion within a macro or command file you need
to use the sqw
function.
Function
example syntax: sqw
w2=sqw(w1,0.02,0.1,-1.0,1.0,0.1,2.0)
Order of arguments: (input workspace, energy increment, Q increment, energy
min, energy max, Q min,Q max)
You should use a course grid whenever possible otherwise the processing
time will be very long. Choose Q max, Q min within the limits of the data.
An aditional argument ,/fast
can be added if the Q,
grid of the input workspace is the same as that
used for a previous call of
sqw
, the same triangles will
then be used, making the calculation faster.
Command
sqwwin
sqwwin
in the formula-entry area will bring up
a special interface to set the arguments for the sqw
function and then perform the calculation.
sqwwin
has been used previously you will get extra
options related to the triangles calculated before. If in doubt, select the
Delete Triangles option. The interface closes when the
calculation is complete.
Normalise to Vanadium (
vnorm
)vnorm
will take the integral of a given
spectral region in one workspace and then divide the corresponding spectra
in a second workspace by this integral.
w3=vnorm(w1,w2,230,250)
Order of arguments: (input workspace, vanadium workspace, lower limit for
integral, upper limit for integral)
You can use this to get s(Q) for either an elastic or inelastic
peak by extracting the spectra of interest
eg.:
w2=w1(150:200,*)
and then normalising:
w4=vnorm(w2,w3,230,250)
Normalise Backscattering Spectra
(
bsnorm
)bsnorm
is used to normalise backscattering
spectra to the monitor spectrum eg. to normalise workspace,w1, and put the
normalised workspace into w2, type
w2=bsnorm(w1)
Line-up Elastic Peaks (
lineup
)lineup
first smoothes each spectrum and then estimates
the position of the maximum. if NOFIT is not present then a gaussian fit is made for all spectra. An average of these positions is taken and then
all spectra are shifted so that their elastic peaks are at the average
position. Any peak which is more than 10 channels away from the elastic-peak
channel given in the parameters is not shifted. The new average peak position
is returned in elas but not entered in the parameters automatically.
w2=lineup(w1, elas [,/nofit])
You can get a quick estimate of the elastic peak position by summing all
spectra (do not include the multidetector on IN5) by entering, for example:
w2=total(w1(*,30:90),2)
The function shift
can then be used to move channels
by a given integer, for example:
w2(*,50)=shift(w1(*,50),3)