New opportunities in quasi elastic neutron scattering spectroscopy

The high energy resolution usually required in quasi elastic neutron scatte ring (QENS) spectroscopy is commonly achieved by the use of cold neutrons. This is one of the important research areas where the majority of current w ork is done on instruments on continuous reactor sources. One particular re ason for this is the capability of continuous source time-of-flight spectro meters to use instrumental parameters optimally adapted for best data colle ction efficiency in each experiment. These parameters include the pulse rep etition rate and the length of the pulses to achieve optimal balance betwee n resolution and intensity. In addition, the disc chopper systems used prov ide perfect symmetrical line shapes with no tails and low background. Recen t development of a set of novel techniques enhance the efficiency of cold n eutron spectroscopy on existing and future spallation sources in a dramatic fashion. These techniques involve the use of extended pulse length, high i ntensity coupled moderators, disc chopper systems and advanced neutron opti cal beam delivery, and they will enable Lujan center at Los Alamos to surpa ss the best existing reactor instruments in time-of-flight QENS work by mor e than on order of magnitude in terms of beam flux on the sample. Other app lications of the same techniques will allow us to combine advantages of bac kscattering spectroscopy on continuous and pulsed sources in order to deliv er mu eV resolution in a very broad energy transfer range. (C) 2001 Elsevie r Science B.V. All rights reserved.