In Al27 (alpha,n): why is a neutron ejected?

Why does a neutron get ejected when Aluminium-27 is hit with an alpha particle?

It seems like:
Al-27 + He-4 –> P-31 (stable) and a gamma/(s) as the nucleus re-arranges. So why eject the neutron and go to the unstable P-30, which then decays by beta+ via:
Al-27 + He-4 –> P-30 + n?

If it helps, this is the context of 6MeV alphas being accelerated at a fixed target, but I guess my question is more the general why eject a neutron and make the unstable isotope? Is this to do with the neutron being pushed out by forward momentum?