Spallation Neutrons and Pressure Diffractometer
SNAP | BL-3 | SNS
As general note, we have now moved to the MANTID software package for most of our data reduction. This makes the reduction of raw data a much easier and automated process for most applications.
Current General Capabilities
- Disordered materials studies (glasses/liquids/sloppy crystals at HP): low-resolution wide Q-range mode, 0.6 < Q < 23 Å-1, at temperatures between 90–300 K and pressures up to 10 GPa.
- Powder crystallographic studies: higher resolution with detectors at 90o. First frame covers 0.5 < d< 3.0 Å. Higher frames can give data up to d = 8 Å, though note that the neutron beam intensity falls off rapidly at these wavelengths, i.e., you will need strong peaks in this range. We can reach pressures up to 25 GPa between 85 and 320 K. Using a pure Zr gasket will allow measurement of weaker, long-wavelength reflections. However, pure Zr will pollute the spectrum with Bragg peaks up to d = 2.8 Å. If a clean low-d spectrum is necessary, another sample in a TiZr gasket will have to be run. Keep this in mind when calculating the number of days needed for an experiment.
- A modified piston for the PE cell allows resonance absorption line width measurements of samples held in a graphite furnace. This allows us to accurately determine the temperature of samples, while measuring in the high-resolution configuration up to 1500 K and ~6 GPa. This technique is currently restricted to powder samples.
Under Development
We are constantly developing diamond anvil cell (DAC) techniques for neutrons and have recently collected powder data on a simple system at room temperature up to 94 GPa. DAC pressure is applied using an external press with an inflatable membrane. This allows for the application of pressure in situ even when the press is connected to a CCR for low temperature studies (7-120 K). Additionally, we have done some high temperature studies (<700 K) in a DAC using external heating.
Please keep in mind that the systems available for study with a DAC are very limited. We need good scatters, simple crystal structures and sample packing. If you have an idea for a DAC experiment, please discuss it with an instrument team member before submitting a proposal.
Policy for the provision of diamond anvil cells (DACs) at the SNAP Beamline
- The need of a Diamond Anvil Cell (DAC) has to be explicitly requested in the beamtime proposal, otherwise the provision of a DAC cannot be guaranteed.
- Users must contact the instrument team as soon as possible (minimum 8 weeks) prior to the beamtime to discuss details of the experiment.
- Users should arrive well in advance for the experiment (typically 2-3 days) and always a full day before beamtime starts.
- Standard SNAP DACs are provided.
- One DAC will be provided per beamtime visit. Its use is solely for the completion of the proposed experiment. Provided that adequate resources and components are available, a second DAC might be available, contingent upon instrument staff approval.
- Samples need to be available at least a week prior to the beamtime to allow for the preparation of the DAC as soon as resources are available.
- In special cases, samples may be requested at the beginning of the cycle for feasibility assessment. Beamtime scheduling may be contingent on those results.
- A successful loading is not guaranteed, especially on the first attempt.
- Unsuccessful preparations may lead to cancellation of the beamtime, and the user should resubmit the (modified) proposal.
- Alternatively, the beamtime can go ahead if there is an approved alternate sample added to the proposal. - Various pressure-transmitting media are available; gas loading has to be requested preferably in the beamtime proposal. It should always be discussed in advance.
- Staff members that make significant contributions for the preparation of the cell and sample loading should be co-authors of any publication resulting from the experiment.
- Any decision regarding any issue that affects the safety of the equipment ultimately lies with the instrument staff.
- The equipment has to be operated under the health and safety rules provided and the advice of the instrument staff must be followed.
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