This page describes a typical procedure for setting up a single-crystal sample, locating nuclear reflections, and determining the UB matrix on HODACA.
The exact procedure depends on the sample, scattering plane, and installed sample environment. If you are unfamiliar with the alignment procedure, please consult the instrument staff.
For sample preparation before arriving at HODACA, see Before Your Experiment.
In SPICE, select New > Experiment, or use the begin command to start a new experiment.
Enter the experiment title, user information, sample information, lattice parameters, scattering plane, and other requested information.
Complete the experiment information within approximately 90 seconds after opening the dialog. If no input is made for too long, the begin procedure is canceled and must be started again.
Create an electronic experiment notebook by copying the HODACA experiment-note template in Google Docs, and enter the experiment information in the header.
Outgoing users are generally expected to return the instrument to the standard handover condition. Nevertheless, always check the instrument state before starting a new experiment. See End of Experiment for the standard handover procedure.
Before aligning a new sample, check whether settings from the previous experiment remain active.
A typical reset includes:
drive e -0.1
drive e 0
hold rx 0 ry 0
drive rx 0 ry 0
drive 1l 1 1t 1 1b 1 1r 1
The first slit is fully open at a blade value of 1.
Approaching E = 0 from a slightly negative energy transfer provides a consistent final approach of the monochromator axes.
If necessary, move A2 and C2 to a known safe position before beginning the alignment. Always consider the installed sample environment and cryostat hoses before making large motor movements.
A2 = 60° and C2 = 30° may be used as a convenient standby position when this position has been confirmed to be safe for the installed sample environment.
drive a2 60 c2 30
If temperature control from the previous experiment is no longer required, the LS335 heater can be turned off using:
ls335range 0
te 1
In the 3341 16-channel counter window, set:
Preset: 1
Repeat: 0
and press Start.
This provides a continuously updating detector monitor that is useful while searching for Bragg peaks.
The CH12 count display corresponds to the detector at the scattering angle represented by the current SPICE A2 setting.
Select a strong nuclear reflection that has been prepared in advance for sample alignment.
Before moving the spectrometer, calculate the expected motor positions using:
cabr h k l
For example:
cabr 1 1 0
Check the calculated A2, C2, and other motor positions and confirm that the requested position is mechanically accessible.
Always check the calculated position before using br.
After confirming that the position is safe, move toward the reflection using:
br h k l
For example:
br 1 1 0
If the initial orientation is only approximate, the actual Bragg peak may be displaced significantly from the calculated C2 position.
Watch the CH12 detector monitor while moving C2 around the expected position.
For example, C2 can be moved relative to its current position using:
driverel c2 -20
The equivalent expression using the current C2 position is:
drive c2 @(c2)-20
Alternatively, move directly to a selected absolute position, for example:
drive c2 -20
or
drive c2 20
Use appropriate step sizes and directions for the expected reflection position rather than moving through a large angular range unnecessarily.
When a cryostat is installed, confirm that all planned C2 motion is safe for the cryostat hoses before making large movements.
Once the Bragg peak becomes visible in the detector monitor, perform a finer C2 scan around the peak.
For example:
scanrelt c2 -1 1 0.1 1
This scans C2 from −1° to +1° relative to the current position with a step of 0.1° and a counting time of 1 s per point.
Adjust the scan range and step size according to the observed peak width.
For C2 scans, scanning from the negative side toward the positive side is generally preferable because it reduces unnecessary backlash motion.
Fit the peak in SPICE and move C2 to the fitted center.
With C2 centered on the reflection, perform a coupled θ–2θ scan.
For example:
th2tht -2 2 0.2 1
Fit the peak in SPICE and move A2 and C2 to the fitted peak position.
The scan range and step size may be adjusted depending on the sample mosaic and observed peak width.
Check the out-of-plane sample alignment by scanning the appropriate goniometer tilt axis, rx or ry.
For example:
scan rx -4 4 1 preset time 1
or
scan ry -4 4 1 preset time 1
Fit the peak and move the corresponding tilt axis to the fitted center.
Use a scan range compatible with the installed sample environment. The available tilt range is smaller for some sample environments.
If you are unsure whether rx or ry corresponds to the required tilt direction, close the neutron shutter and visually check the goniometer before proceeding. Do not move an unfamiliar tilt axis without confirming its direction.
After the sample tilt has been refined, hold the tilt axes before making reciprocal-space moves:
hold rx 1
or
hold ry 1
This prevents reciprocal-space moves such as br from attempting to change rx and ry.
If further tilt adjustment is required later, release the corresponding axis before scanning it:
hold rx 0
or
hold ry 0
After the adjustment, hold the axis again.
Before calculating the UB matrix, check that the lattice parameters used in SPICE are appropriate for the observed reflection.
If necessary, use Sample > Lattice Constant to calculate the relevant lattice parameter from the observed A2 position and update the lattice parameters.
After entering the updated values, use Set Lattice Parameters to apply them to the UB-matrix calculation.
SPICE does not automatically refine the lattice parameters when the UB matrix is calculated.
Open Sample > UB Matrix in SPICE.
Select the one-reflection mode:
Define scattering plane vectors and 1 reflection
Confirm that the scattering-plane vectors and lattice parameters are correct.
With the spectrometer positioned at the optimized first Bragg reflection, enter the correct (h, k, l) indices and select:
using hkl and current motor position
Then click Add.
Confirm that the entered (h, k, l) and the recorded motor positions are correct.
Click:
Calculate UB Matrix / Update Orientation Information
SPICE calculates a provisional UB matrix using the specified scattering plane and the observed position of the first reflection.
Check the calculated information, particularly the calculated h, k, and l values. They should be consistent with the assigned reflection.
If the calculated indices differ significantly from the expected values, check the lattice parameters and reflection assignment and calculate the UB matrix again.
When the result is satisfactory, click Accept Configuration.
The accepted provisional UB matrix can then be used with cabr and br to calculate and reach other reflections in the specified scattering plane.
Choose a second strong nuclear reflection that is well separated from the first reflection in reciprocal space.
Using the provisional UB matrix, calculate its expected position:
cabr h k l
Check the calculated motor positions and confirm that the requested movement is safe.
Then move toward the reflection:
br h k l
Locate and optimize the second reflection in the same way as the first:
locate the peak by moving C2 while watching the detector monitor;
perform a fine C2 scan;
perform a θ–2θ scan; and
refine rx or ry if necessary.
If a held tilt axis must be adjusted, release the corresponding hold before the scan and hold it again after the adjustment.
Open Sample > UB Matrix and select:
Define 2 non-colinear reflections
With the spectrometer positioned at the optimized second reflection, enter the correct (h, k, l) indices.
Select:
using hkl and current motor position
Select Reflection 2, and then click Add to add the second reflection.
Confirm that the (h, k, l) indices and motor positions stored for both Reflection 1 and Reflection 2 are correct.
If ry is nonzero, make sure that the ry value stored for Reflection 1 is also updated to the final tilt value before calculating the two-reflection UB matrix. If another tilt axis has been adjusted after Reflection 1 was added, also check that the stored motor positions for Reflection 1 remain consistent with the final sample orientation.
Click:
Calculate UB Matrix / Update Orientation Information
Check the calculated h, k, and l values for both reflections. They should be close to their assigned indices.
If there is a significant discrepancy, check the lattice parameters, lattice angles, reflection assignments, crystallographic setting, and sample orientation before accepting the result.
When the result is satisfactory, click Accept Configuration.
When the configuration is accepted, SPICE saves the UB configuration as a UB_xxxxxx.ini file in the UBConf directory of the current experiment folder, for example:
...\HODACA\exp111\UBConf\UB_182007.ini
If the UB-matrix setup is canceled instead of accepted, the configuration is not saved.
A saved UB configuration can later be restored using Restore previous orientation.
If the observed position of the second reflection differs systematically from the calculated position, first check the reflection assignment, lattice parameters, lattice angles, and crystallographic setting.
The angle between the two observed reciprocal-space vectors can be checked from:
Sample > Angle Utilities > Calculate angle between Q's with above motor positions
This can be useful when checking whether the crystallographic angles used in SPICE are consistent with the observed angular separation between the two reflections.
After accepting the two-reflection UB matrix, check one or more known nuclear reflections.
First calculate the expected position:
cabr h k l
After confirming that the calculated position is safe, move to the reflection:
br h k l
Confirm that the observed Bragg peak is close to the calculated position.
Do not assume that the UB matrix is correct simply because the calculation completed successfully.
A significant discrepancy may indicate an incorrect reflection assignment, crystallographic setting, lattice parameters, scattering-plane definition, or sample orientation.
If multiple crystallographic settings are commonly used for the material, such as rhombohedral and hexagonal settings, confirm that the same convention is being used consistently in SPICE and in the reflection calculations.
After the sample orientation and UB matrix have been established, perform the standard slit scan.
The slit scan should be performed after the sample has been aligned and a suitable Bragg reflection has been established.
The standard macro is stored in the HODACA directory one level above the experiment data folders.
In SPICE, select Read from File and run:
slit_scan.macro
For details of the slit-scan procedure and slit convention, see Macros & Examples.
After the sample alignment and slit scan have been completed, set the MCU value before starting the main measurement.
The instrument will normally already be at E = 0 after the alignment procedure.
If the current energy transfer is not E = 0, approach the elastic condition from the negative-energy side:
drive e -0.2
drive e 0
Then measure the monitor rate:
count preset monitor 100000
Read the resulting time-act value.
Then set the MCU value so that 1 MCU corresponds to approximately one minute of counting near E = 0.
For example:
mcu 100000/[time-act value]*60
If time-act is 20 s:
mcu 100000/20*60
SPICE evaluates the expression directly.
Confirm the setting using:
count preset mcu 1
Near E = 0, the counting time should be approximately one minute.
At finite energy transfer, the actual counting time for 1 MCU may be longer because the monitor count rate changes with incident energy.
Important: The MCU setting is reset when a new experiment is started with begin. Always check and set the MCU value again before starting measurements with preset mcu.
For further information on MCU counting and measurement-time estimation, see Measurement Examples.
If the 4 K GM refrigerator is being used, start the compressor manually and then set the temperature controller for the first planned measurement temperature.
te 1
ls335range 3
This keeps the temperature-control loop enabled while placing the set point below the achievable base temperature, so that the heater does not intentionally warm the sample during cool-down.
Check the controller state with:
ls335status
Once the required temperature has been reached, set the desired measurement temperature using te.
For other sample environments, use the temperature-control settings specified for that equipment.
Start a new experiment
→ check and reset the instrument state
→ prepare the electronic experiment notebook
→ start the 3341 detector monitor
→ select the first nuclear reflection
→ calculate its position with cabr
→ check the motor positions and mechanical safety
→ move with br
→ locate the Bragg peak by moving C2
→ perform a fine C2 scan
→ perform a θ–2θ scan
→ refine rx or ry
→ hold the sample tilt
→ check and, if necessary, update the lattice parameters
→ add Reflection 1 using the current motor position
→ calculate the provisional UB matrix
→ check the calculated indices
→ Accept Configuration
→ calculate and move toward the second reflection
→ locate and optimize the second reflection
→ select Define 2 non-colinear reflections
→ add Reflection 2 using the current motor position
→ check the stored tilt information for Reflection 1 if necessary
→ calculate the two-reflection UB matrix
→ check the calculated indices
→ Accept Configuration
→ verify the UB matrix using additional nuclear reflections
→ perform the slit scan
→ set the MCU value
→ set/check the temperature controller
→ start the main measurement
Additional information on SPICE operation is available from the following references. Some commands and instrument-specific settings differ between HODACA and other triple-axis spectrometers.
5G-PONTA — SPICE/WASABI
https://sites.google.com/g.ecc.u-tokyo.ac.jp/5g-ponta/software/spicewasabi
SPICE Quick Manual Ver. 1.3 (Japanese)
https://www.issp.u-tokyo.ac.jp/labs/neutron/inst/TASmanual/SPICE_manual_v13.pdf