Maximum neutron density in the He intershell versus normalised model number (proxy for time) showing the last three TPs computed for a 3 M_⊙ AGB star with a PMZ of 2  × 10^-3 M_⊙ (red curve) and a 6.5 M_⊙ model without a PMZ included (blue curve). The peaks are a result of the ²²Ne(α,n)²⁵Mg reaction activated during TPs. For the 3 M_⊙ model the neutron flux during each TPs lasts for  ~4 yr and the total time-integrated neutron flux (neutron exposure τ) is  ~0.02 mbarn^-1. In the 6.5 M_⊙ model the neutron density reaches 10⁹ cm^-3 for  ~ 3 yr and τ ~ 0.2 mbarn^-1. The secondary bumps at  ~10⁷ cm^-3 in the 3 M_⊙ model are a result of the ¹³C(α,n)¹⁶O reaction, which is activated during the interpulse phase due to the PMZ. This activation lasts for  ~30   000 yr and results in τ ~ 0.4 mbarn^-1 (see also Lugaro et al. 2003). The plateaux at  ~10⁶ cm^-3 represent neutrons released during radiative shell He burning in the interpulse periods. These neutron fluxes are insignificant compared to the others (with τ < 0.02 mbarn^-1). Furthermore, the material affected does not make it to the stellar surface as it remains buried in the C–O core. (This figure is available in color in the electronic form.)