Jason Radachy with Arnold Dahm

Directional diffusion of isotropic impurities in an hcp crystal of solid helium

At a certain temperature and pressure, 4He will crystallize in an hcp lattice.  It has been seen that vacancies in a 4He lattice propagate as waves in straight lines along the planes of the crystal.  Previous experiments to measure the parameters of these waves have reported significantly varying results.  This project will measure the parameters of the vacancy waves by doping the solid 4He with 3He, which diffuses throughout the lattice by tunneling into vacancies.  NMR techniques will be used to measure the diffusion rate in a sample of 4He after the spins have been saturated with a large RF pulse.  The diffusion rate will be measured along three orthogonal axes in an effort to prove that the 3He is diffusing anisotropically.