THE TIME-OF-FLIGHT SMALL-ANGLE NEUTRON DIFFRACTOMETER (SAD) AT IPNS, ARGONNE-NATIONAL-LABORATORY

The design, development and performance of the time-of-flight (TOF) sm all-angle diffractometer (SAD) at the Intense Pulsed Neutron Source (I PNS) at Argonne National Laboratory are described. Similar TOE-SANS in struments are in operation at the pulsed neutron sources at Los Alamos National Laboratory, USA, at Rutherford Appleton Laboratory, England, and at KEK, Japan. These instruments have an advantage by comparison with their steady-state counterparts in that a relatively wide range o f momentum transfer (q) can be monitored in a single experiment withou t the need to alter the collimation or the sample-to-detector distance . This feature makes SANS experiments easy and very effective for stud ying systems such as those undergoing phase transitions under differen t conditions, samples that cannot be easily reproduced for repetitive experiments, and systems under high temperature, pressure or shear. Th ree standard samples are used to demonstrate that the quality of the S ANS data from SAD is comparable with those from other established stea dy-state SANS facilities. Two examples are given to illustrate that th e wide q region accessible in a single measurement at SAD is very effe ctive for following the time-dependent phase transitions in paraffins and temperature- and pressure-dependent phase transitions in model bio membranes.