Two-component exciton model for β -delayed neutron emission

A model for $β$-delayed neutron emission is presented in which the emission of neutrons is allowed to occur before states populated in β⁻ decay have reached equilibrium in the so-called "compound nucleus" picture. The pre-equilibrium neutron spectra are computed using a two-component exciton model, where neutron and proton, particle and hole degrees of freedom are treated independently. This model is implemented in the code BeoH to supplement the existing Hauser-Feshbach model for statistical decay of compound-nucleus states. The effect of a pre-equilibrium component in the total neutron spectrum on the single- and multi-neutron emission probabilities Pₓₙ is investigated for $β$-decay precursor nuclei in the regions 47≤ Z≤ 49,~83≤ N≤ 86 and 54≤ Z≤ 58,~N=125,126. An absolute change in the Pₓₙ values of up to 5-10% is observed in the $N=126$ region when including pre-equilibrium emission compared to the values predicted by the Hauser-Feshbach model alone.