Speaker
Description
Neutron capture plays a crucial role in nuclear reactors and nucleosynthesis.
In neutron-rich nuclei near the drip line, the low level density suppresses compound
processes, and direct neutron capture (DC) is expected to contribute significantly to
r-process nucleosynthesis.
A quantitative description of DC requires detailed information on low-lying states
(spectroscopic factors) and resonances.
In this work, we develop a direct neutron capture model based on the continuum
quasiparticle random phase approximation (QRPA).
The present framework consistently describes the collectivity of low-lying states
and resonances, as well as pairing correlations,
with a proper treatment of continuum states.
This approach goes beyond conventional potential (mean-field) models,
which lack many-body correlations and continuum coupling.
We apply this model to neutron-rich nuclei, 89Ge(n,g)90Ge and 91Zn(n,g)92Zn,
using Skyrme energy density functionals (SLy4 and SkM*).
For 89Ge, we find that the pygmy quadrupole resonance enhances the neutron
capture cross section through gamma decay to the collective first 3- state.
For 91Zn, the s-wave capture is enhanced by a quasiparticle resonace,
which originates from a Hartree-Fock bound state that becomes an unbound resonance
due to pairing correlations.
These effects are absent in conventional potential models.
Our results demonstrate that both low-lying collective states and resonances,
including quasiparticle resonances, can play a significant role in direct
(and doorway) neutron capture.