Symmetry and structure tests in 18O and 18Ne

Abstract

Isospin (T) symmetry assumes charge symmetry and charge independence are explicit in nuclear structure. Whereas charge independence implies the nn, np and pp interactions are the same, charge symmetry states that the nn and pp interactions are equal. The latt_er approximate symmetry is experimentally verified by the comparison of the excited levels lying at about the same energy in light mirror nuclei. Both of these symmetries are broken by the electromagnetic interaction. The neutron facility at the University of Kentucky provides a unique opportunity to examine charge independence, and in particular, charge symmetry from the reduced electromagnetic transition probabilities and neutron scattering cross sections. Here, we use the isospin formalism by Bernstein, Brown and Madsen, which relates the proton and neutron matrix elements, M p and M n respectively, for equivalent excited states in T=1 mirror nuclei (Tz = +/−1). The nucleus 18O has been studied using the (n,n′) reaction in order to measure the neutron cross sections of the 21+, T=1 state. Using the previously determined proton matrix elements for the Tz = −1 mirror nucleus (18Ne), along with the determination of the neutron matrix element in 18O from neutron scattering, allows an experimental test of charge symmetry in the A=18 mirror system.