Spin alignment of yrast levels populated by pre-equilibrium (α, xnγ) reactions

Angular momenta of yrast levels following pre-equilibrium (α, xnγ) reactions at E_α, = 110 MeV were found to be aligned as well as those following the equilibrium (compound) (α, xnγ) reactions at E_α = 20–50 MeV. They are uniform against the neutron multiplicity x. The degrees of the spin (angular momentum) alignment with rank 2 for the yrast levels with spins 8–12 average about α₂ ≈ 0.87 ± 0.05. The good spin alignment indicates that both the neutron emission and the γ-emission are stretched in angular momentum space. This supports the pre-equilibrium neutron emission process, where the momenta carried away by the neutrons are not in random directions but rather in the beam direction. The result is well reproduced by the pre-equilibrium neutron emission process followed by neutron evaporation and the K-band γ-deexcitation process.