beta decaying T-1/2=3.4 s isomer in Ni-69 - art. no. 054307

A radioactive beam of Ni-69 was produced by the fragmentation of a 70 MeV/n ucleon Ge-76 beam in a Be target. beta-delayed gamma-ray studies were perfo rmed using two thin plastic scintillators and two large-volume Ge detectors following implantation of the Ni-69 nuclei into a foil of a collection whe el apparatus. A 1296-keV gamma-ray transition with a half-life of 3.4(7) s was identified and has been attributed to the decay of the nu p(1/2)(-1) is omeric state in Ni-69. The relative population of the low-spin J(pi) = 1/2( -) isomer to the known high-spin J(pi) =(17/2(-)) isomer was determined to be 6:1 for the production of Ni-69 via fragmentation of Ge-76, based on an upper limit of 36% extracted for the Ni-69(m1) beta-decay branch to the 3/2 (-) ground state of Cu-69. The half-life and branching of the Ni-69(m1) bet a decay is discussed in light of possible two particle-two hole excitations in the low-energy structure of Cu-69. [S0556-2813(99)05710-6].