ISOSPIN SYMMETRY AND PROTON DECAY: IDENTIFICATION OF THE 10+ ISOMER IN 54Ni

The gamma decays from an isomeric 10(+) state at 6457 keV in the nucleus Ni-54(28)26 have been identified using the GSI fragment separator in conjunction with the RISING Ge-detector array. The state is interpreted as the isobaric analog of the 6527-keV 10(+) isomer in Fe-54(26)28.The results are discussed in terms of isospin-dependent shell-model calculations. Clear evidence is presented for a discrete l = 5 proton decay branch into the first excited 9/2(-) state of the daughter Co-53. This decay is the first of its kind observed following projectile fragmentation reactions.