J. E. Finck

Evidence for the ground-state resonance of 26O.

Evidence for the ground state of the neutron-unbound nucleus (26)O was observed for the first time in the single proton-knockout reaction from a 82 MeV/u (27)F beam. Neutrons were measured in coincidence with (24)O fragments. (26)O was determined to be unbound by 150(-150)(+50) keV from the observation of low-energy neutrons. This result agrees with recent shell-model calculations based on microscopic two- and three-nucleon forces.

Study of Two-Neutron Radioactivity in the Decay of 26O

A new technique was developed to measure the lifetimes of neutron unbound nuclei in the picosecond range. The decay of 26O→24O+n+n was examined as it had been predicted to have an appreciable lifetime due to the unique structure of the neutron-rich oxygen isotopes. The half-life of 26O was extracted as 4.5(-1.5)(+1.1)(stat)±3(syst)  ps. This corresponds to 26O having a finite lifetime at an 82% confidence level and, thus, suggests the possibility of two-neutron radioactivity.

MoNA—The Modular Neutron Array

The Modular Neutron Array (MoNA), a highly efficient time-of-flight neutron detector, is being constructed for use at the National Superconducting Cyclotron Laboratory. The modular design of the detector provides significant flexibility and allows the bulk of the assembly and testing to be done by undergraduates at nine of the schools participating in the project.

Search for 21C and constraints on 22C

A search for the neutron-unbound nucleus

Search for

^{21}

^{21}

C was performed via the single proton removal reaction from a beam of 22 N at 68 MeV/u. Neutrons were detected with the Modular Neutron Array (MoNA) in coincidence with

C and constraints on

^{20}

^{22}

C fragments. No evidence for a low-lying state was found, and the reconstructed

C

^{20}

Three-body correlations in the ground-state decay of 26 O

C+n decay energy spectrum could be described with an s-wave line shape with a scattering length limit of |as| < 2.8 fm, consistent with shell model predictions. A comparison with a renormalized zero-range three-body model suggests that