The study of beta-delayed neutron decay near the neutron drip line

The study of neutron-rich oxygen and fluorine isotopes can provide important information on the evolution of nuclear shell structure close to the neutron drip line. The structural changes in this region are reflected with observations of the rapid change in the location of the drip line at fluorine and appearance of a new shell closure at N = 14. The recent experiments along with the shell model calculations provide evidence for the doubly magic nature of 22O. The negative parity states in 22O rooted in the neutron pf orbitals are not experimentally known. The knowledge of nuclear structure in 23F, which has the structure of a single proton outside the doubly magic 22O, is also important as it should be sensitive to the proton s and d orbital splitting. The present work focused on the beta-delayed neutron and gamma-ray spectroscopes from 22N and 23O beta decay.; The measurements of 22N and 23O were carried out at the NSCL using fragments from the reaction of 48Ca beam in a Be target. The desired isotopes were stopped in the implantation detector and then monitored for beta-delayed neutrons and gamma-rays using a neutron spectroscopic array and eight detectors from SeGA, respectively. The half-lives and the total neutron emission probabilities were determined to be 20(2) and 97(8) ms, and 57(5)% and 7(2)%, respectively, for 22N and 23O. Single and two beta-delayed neutron decay of 22N was observed and five new negative parity states identified in 22O. The measurement also revealed three gamma-ray transitions in 22O and a single gamma-ray for each in 21O and 20O associated with the beta-delayed neutron decay of 22N. Ten gamma-ray decays in 23F and a single gamma-ray in 22 F were observed from 23O beta decay. The tentative decay schemes of 22N and 23O were established and compared with shell model calculations. The beta decays of the major contaminants in the beam from the fragment separator 25F, 24O and 26Ne have been investigated to establish decay schemes as well.; The observation of a relatively high energy for the first 2+ state in 22O supports the shell closure at N = 14. The observation of large beta decay strength at high excitation energies in 22O indicates the indirect evidence for the halo structure of 22N. The experimental results of the 22N beta decay are in poor agreement with the shell model calculations suggesting the evolution of single particle structure in this region. However, the overall beta decay results of 23O are in reasonable agreement with shell model calculations. The excitation energies of the first 1/2+ and 3/2+ states in 23F have been determined at 2243 and 3866 keV and show a widening of the 5/2+ - 1/2+ state gap indicating the appearance of the N = 14 shell closure in the fluorine isotopes.