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Materials Diffractometer

The problem: the NIST high resolution powder diffractometer, BT-1, allows accurate determination of nuclear and magnetic structure across a broad range of materials. Stepping the 32 detectors across a 5° arc affords a high-resolution, complete diffraction pattern suitable for analysis. However, even for sizeable samples, a count time of 2 h to 3 h is required to obtain satisfactory statistics. This greatly limits the nature of the experiments that can be performed.  


The Materials Diffractometer solution: recent technological developments allow an entirely new concept in diffractometer design. We are currently investigating the outcome of using an incident white beam with post-sample wavelength analysis instead of crystal monochromator to condition the neutron beam for diffraction. Although there would be some resolution loss, this option utilizes much more of the incident cold neutron spectrum leading to a significantly increased total neutron flux.  We currently envision the use of relatively inexpensive, high efficiency scintillation detectors covering a wide angular range.  An open instrument layout will provide flexibility for diverse sample environments.  Overall, the increased flux and detector coverage brings the expected measurement time for a single pattern from hours to seconds.  Though the reduction in resolution may limit some structure determination experiments, a whole family of new experiments will be possible, some of which are briefly described below:

  • in-situ reactions and real time experiments: e.g., kinetic studies, gas separation, calorimetry, electrochemical reactions
  • formation and evolution of structures: e.g., gas-solid reactions, glass order transitions, hydrothermal synthesis
  • magnetic structures: evolution of magnetic reflections as a function of temperature, pressure, field, with optional polarization analysis
  • highly absorbing samples: where isotope substitution is not possible
  • very small samples: materials in high pressure cells or under other extreme conditions which limit available sample environment size

Schematic diagram of the instrument layout

MD2



The Materials Diffractometer expected Q ranges at various wavelengths


MD2Qrange

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