First observation of the decay of a 15- seniority v=4 isomer in Sn128

Abstract

Isomeric states in the semimagic 128-130Sn isotopes were populated in the fragmentation of a Xe136 beam on a Be9 target at an energy of 750 A•MeV. The decay of an isomeric state in Sn128 at an excitation energy of 4098 keV has been observed. Its half live has been determined to be T 1/2=220(30) ns from the time distributions of the delayed γ rays emitted in its decay. γγ coincidence relations were analyzed in order to establish the decay pattern of the newly established state toward the known (7-) and (10+) isomers at excitation energies of 2092 and 2492 keV, respectively. Based on a comparison with results of state-of-the-art shell-model calculations the new isomeric state is proposed to have the νh11/2-3d3/2-1 configuration with the four neutron holes in Sn132 maximally aligned to a total spin of Iπ=15-. © 2011 American Physical Society.