Magnetic moment of the 2+ state in the neutron-rich radioactive 72Zn using the High-Velocity Transient-Field technique

We report the first measurement of the g factor of the first 2+ state of the radioactive neutronrich nucleus 72Zn using the High-Velocity Transient-Field (HVTF) technique. The neutron-rich N=40 region has long been discussed regarding the competition between single-particle-like structures in the Ni isotopes and the collective states in their immediate vicinity. Nuclear gyromagnetic factors, with their sensitivity to the single-particle properties of the nuclear states, can be one of the most sensitive probes of this interplay. Whereas the g factors of the 2+ states of the stable Ni isotopes show predominantly single particle behavior, consistent with relatively simple shell model structures [1], those of the nearby Zn and Ge isotopes show a trend consistent with the Z/A rule characteristic of collective states [2]. Particular interest in the Zn isotopes comes about because a number of theoretical calculations predict a change from collective to single-particle dominated behavior in the N=40 region. The main difference between the various models is related to the strength of this change and how sudden or gradual it is expected to be. The last known g factor of the stable isotope 70Zn still implies collective behavior. In the present experiment we have applied the HVTF technique for the first time to nuclei with Z>20 and A>40. As has been demonstrated in the previous measurement of this type [3], the technique can provide a very strong transient magnetic field (TF) for ions traversing ferromagnetic layers with velocities ~Zv0, which in the Z