Magnetic moment of the $13/2{}^{+}$ isomeric state in ${}^{69}\mathrm{Cu}$: Spin alignment in the one-nucleon removal reaction

We report on a new measurement of the $g$ factor of the ($13/2{}^{+}$) isomeric state in the neutron-rich nucleus ${}^{69}\mathrm{Cu}$. This study demonstrates the possibility of obtaining considerable nuclear spin alignment for multi-quasiparticle states in single-nucleon removal reactions. The time-dependent perturbed angular distribution (TDPAD) method was used to extract the gyromagnetic factor of the ($13/2^{+}$) $[T_{1/2}=351\left(14\right)$ ns] isomeric state of ${}^{69}\mathrm{Cu}$. Its $g$ factor was obtained as $g(13/2^{+})=0.248\left(9\right)$. The experimentally observed spin alignment for the state of interest was deduced as $A=-3.3\left(9\right)\%$.

Figure 1

Calculated momentum distribution of ${}^{69}\mathrm{Cu}$ by the lise++ program [20]. A($-1.30\%$), B($-1.19\%$), C($-0.80\%$), D($+0.16\%$), and E($+0.75\%$) correspond to the different momentum selections. The values in the brackets correspond to the central values of each momentum selection with respect to the center of the momentum distribution. The width of the momentum selection was $0.5\%$ in each of the cases.

Figure 2

Schematic drawing of the experimental arrangement of the TDPAD set-up.

Figure 3

Typical $\gamma$-ray energy spectrum in 160–1460 ns time window. Only the most intense $\gamma$ lines are marked. The asterisks, the triangles, and the diamonds indicate, respectively, $\gamma$ rays of ${}^{69m}\mathrm{Cu}$, contamination from $\beta$ decay, ($n,n^{\prime }$) $\gamma$ rays, or natural radioactivities $\gamma$ rays.

Figure 4

Level scheme of ${}^{69}\mathrm{Cu}$ below the ($13/2^{+}$) isomeric state.

Figure 5

Decay curve for the sum of all transitions below the ($13/2^{+}$) isomeric state in ${}^{69}\mathrm{Cu}$.

Figure 6

$R\left(t\right)$ functions for (a) the sum of the $E2$ transitions and (b) the sum of $M1$ transitions following the decay of the ($13/2^{+}$) isomer in ${}^{69}\mathrm{Cu}$ for $\theta =\pm {135}^{\circ }$

detector combination.

Figure 7

Experimental levels of ${}^{69}\mathrm{Cu}$ below the ($13/2^{+}$) isomeric state compared to shell-model calculations using the JUN45 and jj44b interactions.