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 a velocity selector instead of crystal monochromator to condition
the neutron beam for diffraction. Although there would be a significant
resolution loss, this option allows wavelength tuning and an increase
in neutron intensity. The addition of 2D position sensitive detectors
covering a large angular range greatly increases the number of
diffracted neutrons recorded. Overall, the increased flux and detector
coverage brings the measurement time for a single pattern from hours to
seconds. The reduction in resolution will prohibit structure
determination experiments. However, 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, gas-solid reactions, electrochemical reactions
- formation of structures: e.g., glass order transitions, hydrothermal synthesis
- magnetic structures: evolution of magnetic reflections as a function of temperature, pressure, field
- highly absorbing samples: where isotope substitution is not possible
- very small samples: materials in high pressure cells or under other extreme conditions
