Beta Decay Of ~(72)Co And Excited Levels In ~(72)Ni

摘要

An experiment was performed at GANIL to observe isomeric-and beta-delayed gamma rays from very neutron-rich nuclei around ~(74)Ni. Fragmentation products of the ~(86)Kr beam at 58 AMeV were studied using new devices: the LISE 2000 spectrometer and detectors from the EXOGAM germanium array. The primary aim of the experiment was to find the 8~+ microsecond isomer in ~(76)Ni and to perform beta decay spectroscopy of Co nuclei. We have successfully measured the beta delayed gammas from the decay of ~(72)Co to ~(72)Ni. The energies for the lowest excited states in ~(72)Ni are proposed, with the first 2~+ state at 1096 keV. These findings suggest a solution of the problem of the disappearance of the 8~+ isomer in ~(72)Ni. We also measured beta decay of other neutron-rich Co isotopes including ~(70)Co. First evidence was found for a new short lived isomer, most likely the I~π=8~+ state, in ~(76)Ni.