Proper sample preparation and orientation before arriving at HODACA can save a substantial amount of beam time. Please prepare the sample and measurement plan before the scheduled experiment.
Determine the scattering plane required for your experiment before the measurement.
The crystal orientation should be checked in advance using X-ray Laue diffraction or another suitable method. Whenever possible, align the sample to within approximately 1–2° of the intended orientation before mounting it in the sample can. This provides sufficient margin for final adjustment on the spectrometer.
For measurements using the 4 K GM or CTI cryostat, the available goniometer tilt (rx, ry) is approximately ±4°. When the ^3He cryostat is installed, a smaller range of approximately ±2° should be assumed because of the heavier sample environment.
These tilt ranges should be regarded as adjustment ranges rather than substitutes for accurate pre-alignment of the sample.
The crystal should be oriented beforehand and mounted in an appropriate sample can before the experiment.
Do not bring a bare sample to HODACA with the intention of orienting it on the spectrometer. Bare-sample alignment is not permitted.
X-ray Laue measurements can also be performed using the transmission Laue system of the Masuda Group at Kashiwa.
Users should prepare a suitable sample can for their experiment.
Drawings and mounting dimensions for the available sample environments are provided on the Sample Environment page. In particular, check the required sample-center height for the sample environment that will be used.
For cryogenic measurements, helium exchange gas and an indium seal are generally recommended where appropriate.
For high-temperature measurements, do not use an indium seal without confirming its suitability for the planned temperature. Use the sample-holder and sealing method appropriate for the selected sample environment.
If more than one crystallographic setting or indexing convention is commonly used for your material, make sure that the convention used for the experiment is clearly identified.
This is particularly important for structures for which both hexagonal and rhombohedral settings, or other alternative settings, are commonly used.
Use the same convention consistently when preparing the crystal orientation, calculating reflections, defining the scattering plane, and entering the lattice parameters and reciprocal-space vectors in SPICE and analysis software.
Before the experiment, calculate several nuclear reflections that can be used to check and refine the sample orientation.
For elastic alignment on HODACA, Ef = Ei = 3.635 meV meV, corresponding to a neutron wavelength of approximately 4.74 Å. Under this condition, the accessible scattering-angle range extends up to approximately A2 = 105°.
Whenever possible, prepare several strong, well-isolated nuclear reflections within the accessible angular range. Reflections that are well separated in reciprocal space are useful for determining the sample orientation reliably. It is preferable to select reflections with some margin from the mechanical limits rather than relying on positions close to the edge of the accessible range.
If suitable reflections can be reached using the fundamental neutron wavelength, this is generally preferable for routine alignment. Higher-order scattering can extend the accessible Q range, but additional care is required when identifying the observed reflections and possible higher-order contributions.
ASYURA can also be used to estimate the approximate duration of a planned scan.
The calculated time should be regarded as a rough estimate rather than an exact prediction. The actual experiment time depends on the neutron flux, incident energy, motor-motion overhead, temperature changes, sample-environment operation, alignment measurements, and interruptions during the experiment.
For MCU-based measurements, the actual counting time per point also changes with incident energy because the monitor count rate is energy dependent.
For practical guidance on MCU settings and scan-time estimation, see Measurement Examples.
Before arriving at HODACA, please make sure that:
the scattering plane and crystallographic setting have been defined;
the crystal has been pre-aligned by X-ray Laue diffraction or another suitable method;
the sample is mounted in an appropriate sample can;
the sample dimensions and mounting height are compatible with the planned sample environment;
several suitable nuclear reflections for alignment have been calculated;
the approximate Q–E range and measurement sequence have been considered; and
any special sample-environment or mounting requirements have been discussed with the instrument staff in advance.
If you are unsure about sample mounting, orientation, or the planned measurement geometry, please contact the HODACA instrument staff before the experiment.