High Energy Low Temperature Physics: Production of Phase Transitions and Topological Defects by Energetic Particles in Superfluid 3He

I review three sets of experiments conducted in the last decade, in which superfluid 3 He was irradiated with high energy particles and the nucleation either of vorticity or of the A B phase transition reported. I consider how far the known atomic physics constrains possible scenarios for such nucleation, and comment on two such scenarios which have appeared in the literature, namely the "baked Alaska" and "cosmological" (Kibble Zurek Volovik) models. I point out that there is a fundamental difference between the problems of nucleation of vorticity on the one hand and the B phase on the other: and that as a result, it is by no means necessary that the same scenario should describe both phenomena. In an appendix I discuss possible sinks of energy in the calorimetric (Grenoble Lancaster) experiment, with the conclusion that it is entirely consistent with the data to assume that no vorticity at all was produced in this experiment.