Accepted Tuesday Nov 03, 2009
The first spectroscopic study for the b decay of 21N has been carried out based on the b-n, b-g and b-n-g coincidence measurement . The neutron rich 21N nuclei were produced by the fragmentation of the E/A = 68.8 MeV 26Mg primary beam on a thick 9Be target, and were implanted into a thin plastic scintillator which also plays the role of b detector. The time-of-flight of the emitted neutrons following the b decay were measured by the surrounding neutron sphere and neutron wall arrays. In addition four Clover Germanium detectors were used to detect the b-delayed g rays. Thirteen new b-delayed neutron groups were observed with a total branching ratio of 90.5 4.2%. The half-life for the b decay of 21N was determined to be 82.9 7.5 ms. Level scheme of 21O is deduced up to about 9 MeV excitation energy. The experimental results for the b decay of 21N were compared to the shell model calculations.