Roton lifetime measurement in superfluid He-4 using the spin-echo option on the IN20 triple-axis spectrometer

High-resolution measurements of the temperature dependence of the roton lif etime and energy shift in superfluid He-4 have been performed using the IN2 0 thermal neutron triple-axis spectrometer spill-echo option (TASSE). This experiment constitutes the first implementation of the spin-echo technique for inelastic neutron scattering measurements on IN20 using the optimized f ield-shape superconducting precession coils. An energy resolution of 0.7 mu eV was achieved and the results are in agreement with previous studies. Th e use of additional gradient coils enables to substantially improve the ene rgy and the momentum transfer resolution, and to match excitation dispersio n slopes and curvatures. This setup is designed to reach the nano-eV energy resolution in the case of quasi-elastic scattering experiments. (C) 2001 E lsevier Science B.V. All rights reserved.