Neutron studies of liquid and solid helium

The progress made during 5/1/86--4/31/87 under contract No. F902- 34ER45082 is reported. The validity of the Impulse Approximation (IA) to the dynamic form factor, S(Q,ω), has been investigated using realistic models of solid helium. The calculations suggest that the IA can be used to obtain the momentum distribution, n(p), within 1% at Q ∼ 30 Angstrom -1, if S(Q,ω) is first symmetrized about the recoil frequency, ωR. For solid helium under pressure (e.g. 5 kbar) a Q approx-gt 50 Angstrom -1 is required. The S(Q,ω) in liquid 3He and 4He in the wave vector transfer range 3 ≤ Q ≤ 10 Angstrom -1 has been evaluated, beginning from the pair potential. The general shape and width of S(Q,ω) obtained agrees well with existing experiment. The width of S(Q,ω) is found to oscillate as a function of Q in 4He but not in 3He. The dynamics of atoms adsorbed in solid layers on surfaces has been studied using self-consistent methods