Nuclear moments of the low-lying isomeric 1+ state of 34Al: Investigation on the neutron 1p1h excitation across N = 20 in the island of inversion

The nuclear g factor and quadrupole moment ($Q_s$) have been measured for the low-lying isomeric $1^{+}$ state of ³⁴Al, using the β-detected nuclear magnetic resonance (β-NMR) and quadrupole resonance (β-NQR) methods. Spin-polarized ³⁴Al isotopes were produced in a one-neutron pickup reaction induced by a ³⁶S beam on a ⁹Be target at a kinetic energy of 77.5 MeV/nucleon, and were collected with the LISE fragment separator at GANIL. The measured g factor ($\left|g\right|$ in a range of $1.757\pm 0.014$) and quadrupole moment ($\left|Q_s\right|=38\left(5\right)$ mb) are in good agreement with shell-model calculations using effective interactions. The similarity between the g factor of ${}^{34m}$Al and that of ³²Al confirms a dominant neutron $2p1h$ configuration $\pi {\left(d_{5/2}\right)}^{-1}\otimes \nu {\left(d_{3/2}\right)}^{-1}{\left(f_{7/2}\right)}^2$ of ${}^{34m}$Al. In addition, the enhanced quadrupole moment of ${}^{34m}$Al relative to that of ³²Al suggests that the neutron $1p1h$ excitation across the $N=20$ shell gap introduces extra nucleon–nucleon correlation and deformation.