Study of the N=50 major shell effect close to $^{78}$Ni : First evidence   of a weak coupling structure in $^{83}\_{32}$Ge$\_{51}$ and three-proton   configuration states in $^{81}\_{31}$Ga$\_{50}$
  New levels were attributed to $^{81}\_{31}$Ga$\_{50}$ and $^{83}\_{32}$Ge$\_{51}$ which were fed by the $\beta$-decay of their respective mother nuclei $^{81}\_{30}$Zn$\_{51}$ and $^{83}\_{31}$Ga$\_{52}$ produced by fission at the "PARRNe" ISOL set-up installed at the Tandem accelerator of the Institut de Physique Nucl\'eaire, Orsay. We show that the low energy structure of $^{81}\_{31}$Ga$\_{50}$ and $^{83}\_{32}$Ge$\_{51}$ can easily be explained within the natural hypothesis of a strong energy gap at N=50 and a doubly-magic character for $^{78}$Ni. 
D. Verney (IPNO), F. Ibrahim (IPNO), O. Perru (IPNO), O. Bajeat   (IPNO), C. Bourgeois (IPNO), M. Ducourtieux (IPNO), C. Don...