The reduced transition probabilities $B(E2;0_{\text{g.s.}}^{+}\to 2_1^{+},2_2^{+})$ in ${}^{70}\mathrm{Zn}$ and the full $B(E2;0_{\text{g.s.}}^{+}\to 2^{+})$ strength up to ${\mathrm{S}}_n=7.79\mathrm{MeV}$ in ${}^{68}\mathrm{Ni}$ have been determined at the LISE/GANIL facility using the Coulomb-excitation technique at intermediate beam energy on a ${}^{208}\mathrm{Pb}$ target. The $\gamma$ rays emitted in-flight were detected with an array of $46{\mathrm{BaF}}_2$ crystals. The angles of the deflected nuclei were determined in order to disentangle and extract the Coulomb and nuclear contributions to the excitation of the $2^{+}$ states. The measured $B(E2;0_{\text{g.s.}}^{+}\to 2_1^{+})$ of 1432(124) $e^2{\mathrm{fm}}^4$ for ${}^{70}\mathrm{Zn}$ falls in the lower part of the published values which clustered either around 1600 or above $2000e^2{\mathrm{fm}}^4$, while the $B(E2;0_{\text{g.s.}}^{+}\to 2_2^{+})$ of 53(7) $e^2{\mathrm{fm}}^4$ agrees very well with the two published values. The relatively low $B(E2;0_{\text{g.s.}}^{+}\to 2_1^{+})$ of 301(38) $e^2{\mathrm{fm}}^4$ for ${}^{68}\mathrm{Ni}$ agrees with previous studies and confirms a local magicity at $Z=28$, $N=40$. Combining the results of the low-energy spectra of ${}^{68}\mathrm{Ni}$ and ${}^{70}\mathrm{Zn}$ and their shell-model interpretations, it is interesting to notice that four different shapes (spherical, oblate, prolate, and triaxial) are present. Finally, a summed $E2$ strength of only about $150e^2{\mathrm{fm}}^4$ has been found experimentally at high excitation energy, likely due to proton excitations across the $Z=28$ gap. The experimental distribution of this high-energy $E2$ excitation agrees with shell-model calculations, but its strength is about two times weaker.

• Received 19 May 2020
• Revised 8 April 2021
• Accepted 10 September 2021

DOI:https://doi.org/10.1103/PhysRevC.104.034318