ABSTRACT
NIMROD is the Near and InterMediate Range Order Diffractometer of the ISIS second target station. Its design is optimized for structural studies of disordered materials and liquids on a continuous length scale that extends from the atomic, upward of 30 nm, while maintaining subatomic distance resolution. This capability is achieved by matching a low and wider angle array of high efficiency neutron scintillation detectors to the broad band-pass radiation delivered by a hybrid liquid water and liquid hydrogen neutron moderator assembly. The capabilities of the instrument bridge the gap between conventional small angle neutron scattering and wide angle diffraction through the use of a common calibration procedure for the entire length scale. This allows the instrument to obtain information on nanoscale systems and processes that are quantitatively linked to the local atomic and molecular order of the materials under investigation.
ABSTRACT
The three site-site partial structure factors for water have been measured as a function of pressure, using neutron diffraction, at a temperature of 268 K. It is found that the measured structure functions imply a continuous transformation with increasing pressure from a low-density form of water ( rho(L) approximately 0.0295 molecules/A(3)), with an open, hydrogen-bonded tetrahedral structure, to a high-density form of water ( rho(H) approximately 0.0402 molecules/A(3)), with nontetrahedral O-O-O angles and a collapsed second coordination shell, which implies broken hydrogen bonds between the first and second coordination shells.
