Identification of deformed intruder states in semi-magic $^{70}$Ni

and the U. of Maryland -- ANL -- MSU -- U. of Tokyo -- U. of Padua -- LBNL -- U. of Edinburgh -- U. of Aizu -- Orsay -- JAEA -- Central Michigan U. collaboration --- The structure of semi-magic $_{28}^{70}$Ni$_{42}^{{}}$ was investigated following complementary multinucleon-transfer and secondary fragmentation reactions. Changes to the higher-spin, presumed negative-parity states based on observed $\gamma$-ray coincidence relationships improve the agreement with shell-model calculations using effective interactions in the neutron $f_{5/2}pg_{9/2}$ model space. The second 2$^{+}$ and (4$^{+}$) states, however, can only be successfully described when proton excitations across the $Z=28$ shell gap are included. Monte-Carlo shell-model calculations suggest that the latter two states are part of a prolate-deformed intruder sequence, establishing an instance of shape coexistence at excitation energies lower than those observed recently in neighboring $^{68}$Ni.