LCHK - LAUE DATA COLLECTION STRATEGY
This program analyses the distribution of symmetry-unique reflections
in a Laue pattern. LCHK is intended to complement the program NEWLAUE,
and most of the conventions assumed in NEWLAUE are followed in LCHK.
Please note that LCHK always deals with UNIQUE reflections. The program
was originally written by M.Elder and has been revised by I.J. Clifton
and J.W. Campbell subsequently (Daresbury Laboratory).
When the program starts the option menu is displayed on the left.
Options may be selected by typing the first four characters. The
current default option is displayed in square brackets. CTRL/Z
reprints the option menu. This may be necessary on some terminals if
the alpha screen is erased after a plot has been displayed. CTRL/Z may
also be used to cancel any other prompts throughout the program (but
not cancel cursor options).
List of sections:
Parameters
Analysis Commands
Other Commands
This section describes the parameters used by the LCHK program.
List of subsections in this section:
CELL
WMIN
WMAX
DMIN
DISTANCE
RADIUS
SPDR
BMDR
PX
PY
PZ
SYSTEM
LATT
SPINDLE
SCALE
The CELL parameters, A*, B*, C*, ALPHA*, BETA* and GAMMA* are used to
determine the shape of the reciprocal unit cell. Not all these
parameters are needed in more symmetric crystal systems (see SYSTEM).
Each parameter is individually selected by name and the program
prompts for input value (cell length in Angstroms**-1, angles in
degrees).
Note that the cell lengths are subject to the effects of the SCALE
parameter (q.v.)
For some crystal systems only some of the parameters need be defined,
e.g., for Cubic systems only A* is sufficient, B*=A*, C*=A*, ALPHA=90,
BETA=ALPHA, GAMMA=ALPHA are implied. If the user insists in supplying
values to surplus parameters, correct or incorrect ones, the program
will ignore them, in fact it resets them when the calculation starts.
In such cases the list in the Menu and the hard copy will leave the
value field blank.
The minimum wavelength value in Angstroms.
The maximum wavelength value in Angstroms.
This sets the lower limit on the interplanar separations included. To
consider all spots choose DMIN < WMIN/2. High order index planes (and
hence in general weak reflections) will have small interplanar
spacings. The value of DMIN cuts off the spots due to interplanar
spacings smaller than that length (in Angstroms).
Sets crystal to film distance (in mm).
Prompts for radius of the exposed area of the film (in mm).
Topographers Note: The cassette used in topography stations is square
with half-diagonal (equivalent to radius here) of 50mm.
Prompts for reciprocal axis along rotation axis
Prompts for reciprocal axis nearest x-ray beam axis in plane defined
by beam axis and rotation axis.
Prompts for rotation angle phi_x (Deg) about the axis X along the beam
axis. NEWLAUE assumes that the beam is normal to the film. Positive is
clockwise, looking in the same direction as the axis.
Prompts for rotation angle phi_y (Deg.) about axis Y perpendicular
both to the beam and the spindle axis, forming a right-handed set with
these axes. The Y axis corresponds to the x (horizontal) axis of the
coordinate system of the film. Positive is clockwise, looking in the
same direction as the axis.
Prompts for rotation angle phi_z (Deg.) about axis Z along the spindle
axis. This axis corresponds to the y (vertical) axis of the coordinate
system of the film. Positive is clockwise, looking in the same
direction as the axis.
Together with the centring 'LATT' parameter sets the crystal system
and type. Choices for SYSTEM are:
Triclinic
Monoclinic
Orthorhombic
Tetragonal
Hexagonal (includes rhombohedral on hexagonal axes)
Rhombohedral (rhombohedral axes)
Cubic
Sets the centring type of the lattice. Choices are:
A, B, C One-face centred
F All-face centred
I Body centred
R Rhombohedral centring (SYSTEM=hexagonal only)
Defines the value of Spindle angle setting (in Deg). It is used on the
oscillation/Laue camera to rotate the crystal. The spindle axis is
always assumed to be perpendicular to the beam. It defines the Z axis
and hence the Y axis (see PY, PZ). Clockwise is positive.
This is a scaling factor which applies to the reciprocal cell lengths.
It can be used to speed up the calculations by making LCHK consider a
unit cell which is some fraction of the real one. The results of LCHK
should not change much as SCALE is altered, but some care may be
needed interpreting the results when SCALE is not 1.
The commands described in this section all vary one or more parameters and
produce tables of those parameters against the number of uniques
recorded.
List of subsections in this section:
ROTATE
SEARCH
WAVVAR
VARCF
RESOLN
This command has unfortunately not been documented.
This varies PZ (along the spindle) and PY independently and produces a
matrix of the number of uniques at each step. NB The current value of
SPINDLE is ignored in this option --- the values of PZ are therefore
`absolute'.
This command is concerned with those unique reflections which have
symmetry equivalents (`duplicates') recorded on the same film, and the
wavelength differences within these sets of spots. The program first
calculates the number of such sets of reflections and the total number
of such reflections. For each set of a unique and its duplicates, it
calculates an average wavelength, and accumulates the average
deviation of the set from that average. It then prints out a histogram
of the deviations.
Increases the crystal-film distance in steps starting from its current
value.
This command partitions the uniques into resolution bins (running from
DMIN to the lowest resolution found (dmax)). A table of cumulative
fractions of the uniques is produced, running from dmin to dmax and
vice versa.
Thsi section describes the other commands avaialble within the program
LCHK.
List of subsections in this section:
DATGET
DATSAV
HELP
STOP
The DATGET command allows the user to retrieve data created by a
previous run of the program or in user edited file.
The extension ".dat" is automatically added to the file name.
**** ONLY FILES IN CURRENT DIRECTORY ARE ACCEPTED. ****
A badly formatted file is likely to result in the program crashing.
The DATSAV command allows the user to save the data currently in use
concerning the experimental set-up in a file. It can be retrieved
using DATGET (q.v.)
**** The extension, ".dat" is always added to the file name. ***
**** ONLY FILES IN CURRENT DIRECTORY ARE ACCEPTED ***
The HELP command has now been withdrawn as its impementation was Vax
specific. The information that was presented is now available in this
documentation file.
Ends the program and resets the screen. If you abort the program by
using the CTRL/C or CTRL/Y keys you will need to reset the terminal
manually with the SETUP, RESET keys.
John W. Campbell
CCLRC Daresbury Laboratory
Last update 21 Aug 1996