In an experiment with the RIKEN projectile fragment separator called BigRIPS at the RIKEN Nishina Center, the fragmentation of a ${}^{78}\mathrm{Kr}$ beam allowed the observation of new neutron-deficient isotopes at the proton drip line. Clean identification spectra could be produced and ${}^{63}\mathrm{Se},{}^{67}\mathrm{Kr}$, and ${}^{68}\mathrm{Kr}$ were identified for the first time. In addition, ${}^{59}\mathrm{Ge}$ was also observed. Three of these isotopes, ${}^{59}\mathrm{Ge},{}^{63}\mathrm{Se}$, and ${}^{67}\mathrm{Kr}$, are potential candidates for ground-state two-proton radioactivity. In addition, the isotopes ${}^{58}\mathrm{Ge},{}^{62}\mathrm{Se}$, and ${}^{66}\mathrm{Kr}$ were also sought but without success. The present experiment also allowed the determination of production cross sections for some of the most exotic isotopes. These measurements confirm the trend already observed that the empirical parametrization of fragmentation cross sections, EPAX, significantly overestimates experimental cross sections in this mass region.

• Received 11 April 2016

DOI:https://doi.org/10.1103/PhysRevC.93.061301