Abstract
A characteristic feature of collective and particle-hole excitations in neutron-rich nuclei is that many of them couple to an unbound neutron in continuum single-particle orbits. The continuum random-phase approximation (cRPA) is a powerful many-body method that describes such excitations, and it provides a scheme to evaluate transition strengths from the ground state. In an attempt to apply cRPA to the radiative neutron-capture reaction, we formulate in the present study an extended scheme of cRPA that describes transitions from the excited states under consideration, which decay to low-lying excited states as well as the ground state. This is achieved by introducing a nonlocal one-body operator which causes transitions to a low-lying excited state, and describing a density-matrix response against this operator. As a demonstration of this new scheme, we perform numerical calculation for dipole, quadrupole, and octupole excitations in , and discuss and transitions decaying to low-lying and states. The results point to cases where the branching ratio to the low-lying states is larger than or comparable with that to the ground state. We discuss key roles of collectivity and continuum orbits in both initial and final states.
5 More- Received 1 May 2021
- Accepted 17 August 2021
DOI:https://doi.org/10.1103/PhysRevC.104.034305
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