First observation of the decay of a 15{sup -} seniority v=4 isomer in {sup 128}Sn

Isomeric states in the semimagic {sup 128-130}Sn isotopes were populated in the fragmentation of a {sup 136}Xe beam on a {sup 9}Be target at an energy of 750 A{center_dot}MeV. The decay of an isomeric state in {sup 128}Sn at an excitation energy of 4098 keV has been observed. Its half live has been determined to be T{sub 1/2}=220(30) ns from the time distributions of the delayed {gamma} rays emitted in its decay. {gamma}{gamma} coincidence relations were analyzed in order to establish the decay pattern of the newly established state toward the known (7{sup -}) and (10{sup +}) 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 {nu}h{sub 11/2}{sup -3}d{sub 3/2}{sup -1} configuration with the four neutron holes in {sup 132}Sn maximally aligned to a total spin of I{sup {pi}}=15{sup -}.