One-neutron removal and reaction cross sections for ¹⁶N(0^-) isomeric state

The isomeric state of nuclei is a very important subject of study, not only because it is of interest for its peculiar nuclear structure, but also because it can affect nucleosynthesis in the universe. For example, the population of isomeric states in hot stellar interiors can be comparable to that of the ground state, and the capture cross section of a core nucleus for a neutron(proton) is greatly increased if the valence nucleon is in a halo state. We focused on the isomeric state of ¹⁶N and performed the following experiments to confirm the possibility that the valence neutron in that state is like a neutron halo. We have already measured the isomer ratios of ¹⁶N secondary beams produced by irradiating 160 MeV/u ¹⁸O and 169 MeV/u ¹⁵N beams on Be targets and found them to be 22% and 8%, respectively.

We measured the one-neutron removal and reaction cross sections for these two ¹⁶N secondary beams and extrapolated them as a function of the isomer ratio to derive the isomer and ground-state cross sections, respectively. As a result, it was found that isomer and ground state cross sections differ by up to 40% in the one-neutron removal cross section. In the presentation, we will discuss the results of the analysis in comparison with the Glauber calculation taking into account Coulomb breakup reactions.