  In an experiment with the BigRIPS separator at the RIKEN Nishina Center, the
fragmentation of a $^{78}$Kr beam allowed the observation of new
neutron-deficient isotopes at the proton drip-line. Clean identification
spectra could be produced and $^{63}$Se, $^{67}$Kr, and $^{68}$Kr were
identified for the first time. In addition, $^{59}$Ge was also observed. Three
of these isotopes, $^{59}$Ge, $^{63}$Se, and $^{67}$Kr, are potential
candidates for ground-state two-proton radioactivity. In addition, the isotopes
$^{58}$Ge, $^{62}$Se, and $^{66}$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 parameterization of fragmentation cross
sections, EPAX, significantly overestimates experimental cross sections in this
mass region.
