Two new proton-rich isotopes, Germanium-60 and Selenium-64, were observed for the first time at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. These very rare isotopes were produced by a krypton-78 beam impinging upon a beryllium target. Out of the many species produced in a projectile fragmentation process the very proton-rich isotopes were selected by the A1900 fragment separator. The produced isotopes were unambiguously identified by detector systems installed in the fragment separator. Figure 1 shows a particle identification plot for a separator setting optimized for germanium-60.
The discovery of new nuclei along and beyond the proton dripline is crucial for the understanding of the nuclear forces and the formation of the elements. From the observation or non-observation of nuclei produced in projectile fragmentation reactions, lifetimes or lifetime limits can be extracted. Lifetime information of new nuclei can be used to constrain the mass models, because the proton decay lifetimes are correlated with the binding energies. The knowledge of the binding energies of the extremely neutron-deficient nuclei can be used to change the mass model predictions for the astro-physical rapid proton capture process nuclei from extrapolations to interpolations.
This work was supported by the National Science Foundation through grant PHY 0110253.
A. Stolz et al., Phys. Lett. B 627 (2005) 32.
stolz at nscl.msu.edu, 517-324-8121