Proof-of-principle Experiment of ⁴He Excimer Cluster Generation via Neutron-³He Absorption Reaction for Visualization of Velocity Fields in Superfluid ⁴He

Abstract

For visualization of flows in superfluid ⁴He, an excited helium molecule (excimer) ⁴He₂^* is an ideally suitable flow tracer, because it has a molecular size with a minimum influence to flow, and follows only normal-component flow around 1K but only vortices below 0.5 K. However, to visualize flow fields in 3D, small clouds (clusters) of ⁴He₂^* are required, whose generation method has not been established. To generate such clusters, we proposed the use of neutron-³He absorption reaction. In the proof-of-principle experiments, we have confirmed the ⁴He₂^* generation, while the detail of clusters still remains undetermined. The concept, methods, progress, and present status are shown.