Discovery of Ca-60 and Implications For the Stability of Ca-70

The discovery of the important neutron-rich nucleus Ca-60(20)40 and seven others near the limits of nuclear stability is reported from the fragmentation of a 345 MeV= u Zn-70 projectile beam on Be-9 targets at the radioactive ion-beam factory of the RIKEN Nishina Center. The produced fragments were analyzed and unambiguously identified using the BigRIPS two-stage in-flight separator. The eight new neutron-rich nuclei discovered, P-47, S-49, Cl-52, Ar-54, K-57, Ca-59,Ca-60, and Sc-62, are the most neutron-rich isotopes of the respective elements. In addition, one event consistent with K-59 was registered. The results are compared with the drip lines predicted by a variety of mass models and it is found that the models in best agreement with the observed limits of existence in the explored region tend to predict the even-mass Ca isotopes to be bound out to at least Ca-70.