| Secondary, radioactive ion beams of 19N and 20 N were produced at the National Superconducting Cyclotron Laboratory at Michigan State University by fragmenting a primary beam of 22Ne (80 MeV/A) in a beryllium target. The isotopes of interest were implanted within a plastic scintillator and their decay was monitored. Beta events were recorded by the implantation scintillator, delayed-neutron emission was observed by the neutron bar array as well as three 6Li inorganic scintillators, and gamma-ray events were recorded by two germanium detectors. Quantitative measurements of the branching ratios for delayed-neutron and gamma ray emission were made for both 19N and 20 N, and the half-lives of the species were deduced. The 19N data suggests that there are twelve delayed-neutrons emitted during the decay comprising 50.9(62)% of the total decay strength. The gamma-ray spectroscopy yields several branches to bound, excited levels of 19O contributing 39.4(38)% of the total decay strength. There is also evidence of significant delayed-neutron emission to bound excited states of 18O. The half-life is determined to be 299(19) milliseconds and the ground state spin and parity is restricted to (1/2- or 3/2-). From the delayed-neutron data, the resonant capture strength for the 18O(n,γ) 19O reaction has been estimated and found not to compete well with the direct capture component except at the highest temperatures possible during the Inhomogeneous Big Bang scenario. The measured branching ratios and inferred properties of the populated intermediate states do not compare well with shell model predictions.; The 20N data suggests eight delayed-neutron branches with energies in excess of 1.1 MeV. Above this threshold, delayed neutron emission accounts for 34.0(40)% of the total decay strength. The gamma-ray analysis leads to 27.0(46)% of the decay proceeding through bound excited states of the 20O daughter. There is also evidence that delayed-neutron emission to 180 populates excited bound states rather than the ground state. The half-life has been re-measured to be 121(15) milliseconds and the ground state spin and parity of 20N is restricted to be low-spin, most likely (1-). |
