Medium-spin states in neutron-rich83As and81As

The ${}^{83,81}\phantom{\rule{-0.16em}{0ex}}$As nuclei have been produced as fission fragments in the fusion reaction ${}^{18}$O + ${}^{208}$Pb at 85 MeV bombarding energy and studied with the Euroball array. Medium-spin states of ${}^{83,81}\phantom{\rule{-0.16em}{0ex}}$As have been established up to $\ensuremath{\sim}3.5$ MeV excitation energy. From angular correlation analysis, spin values have been assigned to most of the ${}^{81}\phantom{\rule{-0.16em}{0ex}}$As excited states. The behaviors of the yrast structures identified in this work are discussed in comparison with the general features known in the mass region. Then they are compared to the results of two theoretical approaches: the ``rotor + quasiparticle'' for ${}^{81}\phantom{\rule{-0.16em}{0ex}}$As and the shell model using the effective interactions JUN45 for ${}^{83,81}\phantom{\rule{-0.16em}{0ex}}\phantom{\rule{-0.16em}{0ex}}$As.