βdecayingT1/2=3.4s isomer in69Ni

Abstract

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