Big bang simulation in superfluid 3He-B -- Vortex nucleation in neutron-irradiated superflow

TL;DR

This study demonstrates vortex nucleation in superfluid helium-3 B triggered by neutron irradiation, revealing how vortex rings form and grow during rapid cooling, with implications for understanding defect formation in phase transitions.

Contribution

It provides experimental evidence of vortex formation due to neutron-induced heating and cooling in superfluid helium-3 B, linking vortex nucleation to rapid phase transition dynamics.

Findings

Vortex rings grow under superflow and escape into the container.

Larger superflow velocities produce smaller vortex rings.

Vortex nucleation is linked to rapid cooling through the superfluid transition.

Abstract

We report the observation of vortex formation upon the absorption of a thermal neutron in a rotating container of superfluid $^3$He-B. The nuclear reaction n + $^3$He = p + $^3$H + 0.76MeV heats a cigar shaped region of the superfluid into the normal phase. The subsequent cooling of this region back through the superfluid transition results in the nucleation of quantized vortices. Depending on the superflow velocity, sufficiently large vortex rings grow under the influence of the Magnus force and escape into the container volume where they are detected individually with nuclear magnetic resonance. The larger the superflow velocity the smaller the rings which can expand. Thus it is possible to obtain information about the morphology of the initial defect network. We suggest that the nucleation of vortices during the rapid cool-down into the superfluid phase is similar to the formation of defects during cosmological phase transitions in the early universe.