We discuss the first experimental observations of a deficit in the thermal energy released after the exothermic neutron-He-3 nuclear reaction in superfluid He-3 at temperatures approaching 100 mu K. We propose that this deficit is associated with the creation of a vortex tangle as the liquid He-3 recrosses the superfluid transition. This process has many similarities with the theory of cosmic string creation during the GUT and electro weak transitions shortly after the Big Bang. Our measurements constitute the first quantitative test of defect creation via the cosmological Kibble mechanism for gauge symmetry breaking phase transitions and agree very well with the predictions of Zurek's scenario.