Kippenhahn diagram illustrating key features of a PIE in a non-rotating 1 M_⊙, [Fe/H] = −2.5 AGB model, computed with the STAREVOL code. Grey regions indicate convective zones. The dashed green (blue) line marks the location of maximum H-burning (He-burning) energy. The colour map shows the neutron density. The time between the peak neutron density and the split is Δt₁ ≃ 100 h, while the total duration of the sequence shown is Δt₂ ≃ 0.1 yr.