Structure effects in the $^{15}$N($n,\gamma$)$^{16}$N radiative capture reaction from the Coulomb dissociation of $^{16}$N

TL;DR

This study calculates the neutron capture cross section for $^{15}$N to $^{16}$N using Coulomb dissociation, investigates spectroscopic factors, and emphasizes the importance of low-energy data for astrophysical reaction rates.

Contribution

It introduces a quantum mechanical Coulomb breakup approach to indirectly determine the $^{15}$N($n, \gamma$)$^{16}$N cross section and examines spectroscopic factors from experiments and shell model predictions.

Findings

Data favors a single particle nature for low-lying $^{16}$N states.

Reaction rate is dominated by capture cross sections below 0.25 MeV.

Resonant contributions are significant only above 1 GK.

Abstract

Purpose : The aim of this paper is to calculate the $^{15}$N($n, \gamma$)$^{16}$N radiative capture cross section and its subsequent reaction rate by an indirect method and in that process investigate the effects of spectroscopic factors of different levels of $^{16}$N to the cross section. Method : A fully quantum mechanical Coulomb breakup theory under the aegis of post-form distorted wave Born approximation is used to calculate the Coulomb breakup of $^{16}$N on Pb at 100 MeV/u. This is then related to the photodisintegration cross section of $^{16}$N($\gamma, n$)$^{15}$N and subsequently invoking the principle of detailed balance, the $^{15}$N($n, \gamma$)$^{16}$N capture cross section is calculated. Results : The non-resonant capture cross section is calculated with spectroscopic factors from the shell model and those extracted (including uncertainties) from two recent experiments. The data seems to favor a more single particle nature for the low-lying states of $^{16}$N. The total neutron capture rate is also calculated by summing up non-resonant and resonant (significant only at temperatures greater than 1 GK) contributions and comparison is made with other charged particle capture rates. In the typical temperature range of $0.1-1.2$ GK, almost all the contribution to the reaction rate comes from capture cross sections below 0.25 MeV. Conclusion : We have attempted to resolve the discrepancy in the spectroscopic factors of low-lying $^{16}$N levels and conclude that it would certainly be useful to perform a Coulomb dissociation experiment to find the low energy capture cross section for the reaction, especially below 0.25 MeV.