This work was partly supported by the U.S. National Science Foundation awards NSF PHY-1565546, NSF PHY-1936404, NSF PHY-2011265, NSF PHY-2011398, and NSF PHY-2012040.
Spectroscopy of neutron unbound 13Be can provide insights into the unexpected structural changes of neutron-rich nuclei around N=8. Invariant mass spectra from past experiments do not agree on the location of the 1/2- p-wave that is expected to strongly decay to a long-lived 02+ state in 12Be with a mean lifetime of 331(12) ns. Its decay scheme has a 20% branch through the 12Be(2+ ) to the ground state, giving a 2.1 MeV gamma ray, and 80% for an E0 transition giving two 511 keV gamma rays from positron annihilation. An experiment was performed by the MoNA Collaboration at the National Superconducting Cyclotron Laboratory of Michigan State University to study the one neutron decay of 13Be to this isomeric state in 12Be. The experiment featured a new telescope to identify the 12Be fragment, and utilizes 96 modules of the MoNA-LISA neutron array as well as the gamma ray detector CAESAR. The latter was placed around the telescope due to the long lifetime of the expected isomer. An overview and preliminary results of the experiment will be presented and discussed.