In-beam gamma-ray spectroscopy of one-neutron knockout channel from $^{36}$Mg

An in-beam gamma-ray spectroscopy via one-neutron knockout reaction of $^{36}$Mg was performed at RIBF to clarify the neutron single-particle configuration in $^{36}$Mg. Neutron-rich Mg isotopes around $^{32}$Mg are known to have a collective nature in spite of the shell-model magic number $N = 20$. In the more neutron-rich region than this area so-called ``island of inversion,'' the deformation persists toward the $N = 28$ region. The large collectivity in the island of inversion is well explained with $\nu(sd)^{-2}$-$(fp)^{+2}$ particle-hole intruder configurations across the $N = 20$ shell gap. One-neutron knockout reactions are sensitive to the neutron single-particle configuration, and may therefore reveal the microscopic driving force for the large collectivity in the neutron-rich Mg isotopes towards $N = 28$. The level scheme of $^{35}$Mg deduced experimentally will be discussed.