Observation of Ground-State Two-Neutron Decay

Neutron decay spectroscopy has become a successful tool to explore nuclear properties of nuclei with the largest neutron-to-proton ratios. Resonances in nuclei located beyond the neutron dripline are accessible by kinematic reconstruction of the decay products. The development of two-neutron detection capabilities of the Modular Neutron Array (MoNA) at NSCL has opened up the possibility to search for unbound nuclei which decay by the emission of two neutrons. Specifically this exotic decay mode was observed in 16Be and 26O.Comment: To be published in Acta Physica Polonica

Exploring the neutron dripline two neutrons at a time: The first observations of the 26O and 16Be ground state resonances

The two-neutron unbound ground state resonances of $^{26}$O and $^{16}$Be were populated using one-proton knockout reactions from $^{27}$F and $^{17}$B beams. A coincidence measurement of 3-body system (fragment + n + n) allowed for the decay energy of the unbound nuclei to be reconstructed. A low energy resonance, $<$ 200 keV, was observed for the first time in the $^{24}$O + n + n system and assigned to the ground state of $^{26}$O. The $^{16}$Be ground state resonance was observed at 1.35 MeV. The 3-body correlations of the $^{14}$Be + n + n system were compared to simulations of a phase-space, sequential, and dineutron decay. The strong correlations in the n-n system from the experimental data could only be reproduced by the dineutron decay simulation providing the first evidence for a dineutron-like decay.Comment: Invited Talk given at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

One- and two-neutron removal cross sections of O 24

© 2018 American Physical Society. Cross sections of one- and two-neutron removal reactions of O24, leading to the O23(12+) ground state and to bound final states of O22, have been measured at the National Superconducting Cyclotron Laboratory. The experiment was conducted using the S800 spectrograph and a O24 beam energy of 92.3 MeV/u. The measured O23 ground state and O22 inclusive cross section values, of 74(11) and 146(33) mb, respectively, are in good agreement with calculations using eikonal reaction dynamics and shell-model nuclear structure overlaps. The widths at half maximum of the associated parallel momentum distributions of these cross sections, deduced from Gaussian fits, are 115(13) MeV/c for O23 and 309(36) MeV/c for O22 in the projectile rest frame. The data and calculations strongly support the shell-model description of O24 as a spherical, doubly-magic structure

Evidence for the Ground-State Resonance of O-26

Evidence for the ground state of the neutron-unbound nucleus O-26 was observed for the first time in the single proton-knockout reaction from a 82 MeV/u F-27 beam. Neutrons were measured in coincidence with O-24 fragments. O-26 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