Neutron Emission from the Isomeric Beta-decays of Co-70 measured by VANDLE at NSCL*

Co-70 beta-decays to Ni-70 by way of two isomers, a (6-) isomer with a half-life of 112ms, and a lower spin isomer listed as (3+) with a half-life of 470ms. As the Q-value for the decay of Co-70 to Ni-70 is 12.6 MeV, and the neutron separation energy of 70Ni is 7.3 MeV, neutron emission is energetically possible. As the two beta-decays of Co-70 have a different structure, it is not certain how both will emit neutrons. Neutron emission may also compete with gamma emission to below the neutron separation energy in the beta-decay child. This neutron emission probability depends on the structure of the beta-decay child (Ni-70) and the properties of the neutron emission product (Ni-69). An array of 42 120cm VANDLE bars were used with a YAP(Yttrium Aluminum Perovskite) inorganic scintillator implant detector to measure both the implanted nuclei from the NSCL fragmentation of the 82Se primary beam and their subsequent beta-decay. Analysis of the Co-70 decays resulted in two distinctly different neutron energy spectra associated with the different half-lives. These spectra were compared with a recently developed model, which combines shell model and statistical model calculations.