The influence of the Coulomb exchange term on nuclear single-proton resonances

TL;DR

This study examines how including the Coulomb exchange term affects single-proton resonance energies and widths in nuclei, revealing a consistent reduction in both, with effects varying by isotope and nuclear properties.

Contribution

The paper introduces a combined complex scaling and relativistic mean-field approach to quantify Coulomb exchange effects on nuclear resonances, which are often neglected.

Findings

Coulomb exchange reduces resonance energy by 0.4-0.6 MeV.

Resonance width decreases, influenced by neutron and proton numbers.

Effect on width varies among different nuclei and states.

Abstract

Nuclear single-proton resonances are sensitive to the Coulomb field, while the exchange term of Coulomb field is usually neglected due to its nonlocality. By combining the complex scaling method with the relativistic mean-field model, the influence of the Coulomb exchange term on the single-proton resonances is investigated by taking Sn isotopes and $N=82$ isotones as examples. It is found that the Coulomb exchange term reduces the single-proton resonance energy within the range of $0.4-0.6$ MeV, and lead to similar isotopic and isotonic trends of the resonance energy as those without the Coulomb exchange term. Moreover, the single-proton resonance width is also reduced by the Coulomb exchange term, whose influence generally decreases with the increasing neutron number and increases with the increasing proton number. However, the influence of the Coulomb exchange term cannot change the trend of the resonance width with respect to the neutron number and proton number. Furthermore, the influence of the Coulomb exchange term on the resonance width is investigated for the doubly magic nuclei $^{40}$Ca, $^{56,78}$Ni, $^{100,132}$Sn, and $^{208}$Pb. It is found that the Coulomb exchange term reduces the proton resonance width within $0.2$ MeV, whose magnitude depends on the specific nucleus and the quantum numbers of resonant states.