Shell evolution beyond $N=40:$ ${}^{69,71,73}\mathrm{Cu}$

The level structure of the neutron-rich ${}^{69}\mathrm{Cu},{}^{71}\mathrm{Cu},$ and ${}^{73}\mathrm{Cu}$ isotopes has been investigated by means of multinucleon transfer reactions. The experiment was performed at Laboratori Nazionali di Legnaro using the AGATA Demonstrator array coupled to the PRISMA magnetic spectrometer. Lifetimes of excited states in Cu nuclei were measured with the recoil-distance Doppler-shift method. The resulting electromagnetic matrix elements for transitions from excited states in ${}^{69,71,73}\mathrm{Cu}$ nuclei are used to assess the collective or single-particle character of these states. The results are compared with predictions of large-scale shell-model calculations, giving further insight into the evolution of the proton $pf$ shell as neutrons fill the $1g_{9/2}$ orbital.

Figure 1

Energy loss $\Delta E$ versus total energy $E$ of the ions detected at the PRISMA focal plane for the ${}^{76}\mathrm{Ge}$ + ${}^{238}\mathrm{U}$ reaction. The elements corresponding to the different proton stripping channels are indicated.

Figure 2

Mass distribution of Cu isotopes detected in PRISMA, showing the selection of three Cu isotopes (upper panel), and Doppler-corrected $\gamma$-ray spectra with fast (f) and slow (s) components for the associated transitions summed over all target-to-degrader distances (lower panel).

Figure 3

Doppler-corrected $\gamma$-ray spectra for ${}^{69}\mathrm{Cu}.$ The positions of the fast (f) and slow (s) components of the 1711-keV $7/2_1^{-}\to 3/2_1^{-}$ transition are indicated by the dashed lines.

Figure 4

Experimental $R\left(t\right)$ values as a function of the flight time between the target and degrader foils for the $7/2_1^{-}\to 3/2_1^{-}$ state in ${}^{69}\mathrm{Cu}$ and the result of the exponential fit. The data point corresponding to the distance at 1900 $\mu \mathrm{m}$ is excluded in the lifetime analysis.

Figure 5

Doppler-corrected $\gamma$-ray spectra for ${}^{71}\mathrm{Cu}.$ The positions of the fast (f) and slow (s) components of the 981-keV $7/2_1^{-}\to 3/2_1^{-}$ transition are indicated by the dashed lines.

Figure 6

Experimental $R\left(t\right)$ values for the $B(E2;7/2_1^{-}\to 3/2_1^{-})$ transition in ${}^{71}\mathrm{Cu}$ as a function of the flight time between the target and degrader foil, and the result of the exponential fit.

Figure 7

Doppler-corrected $\gamma$-ray spectra for ${}^{73}\mathrm{Cu}.$ The positions of the fast (f) and slow (s) components of the 1132-keV $7/2_3^{-}\to 5/2_1^{-}$ transition are indicated by the dashed lines.

Figure 8

Experimental $R\left(t\right)$ values for the $B(E2;(7/2_3^{-})\to 5/2_1^{-})$ transition in ${}^{73}\mathrm{Cu}$ as a function of the flight time between the target and degrader foil, and the result of the exponential fit.