We calculate the low-lying ${B(E2,0\mathrm{}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{+}\to 2_{\mathrm{f}}^{+})$ distribution of strength in ${}^{68}\mathrm{Ni}$ and other nickel isotopes using several theoretical approaches. We find that in ${}^{68}\mathrm{Ni}$ the calculated $B\left(E2\mathrm{}\right)\mathrm{}$ transition to the first $2^{+}$ state exhausts only a fraction of the low-lying $B\left(E2\mathrm{}\right)\mathrm{}$ strength, while the remainder of the low-lying strength is mainly collected in the group of states lying above 4 MeV. This fragmentation is sensitive to the size of the $N=40\mathrm{}$ gap. We argue that the small experimental $B\left(E2\mathrm{}\right)\mathrm{}$ value to the first $2^{+}$ state is not a strong evidence for the double-magic character of ${}^{68}\mathrm{Ni}.$

• Received 31 October 2002

DOI:https://doi.org/10.1103/PhysRevC.67.044314