Quadrupole collectivity in island-of-inversion nuclei 28,30Ne and 34,36Mg

The quadrupole collectivity of neutron-rich even-even neon and magnesium nuclei around N=20, 28,30Ne, and 32,34,36Mg, was studied via proton inelastic scattering on a liquid hydrogen target by in-beam γ-ray spectroscopy in inverse kinematics. The angle-integrated cross sections for the first 2+ states of these nuclei were determined by measuring de-excitation γ rays. The deformation lengths were extracted from the angle-integrated cross sections using distorted-wave calculations. The deformation length of 30Ne (δ(p,p′)=1.59-0.09+0.08 fm) is smaller than that of 32Mg (1.83-0.11+0.10 fm), which exhibits the largest quadrupole collectivity among the neutron-rich N=20 isotones. Along the magnesium isotopic chain, the deformation lengths of 34Mg and 36Mg were deduced to be 2.30-0.10+0.09 fm and 1.90-0.17+0.16 fm, respectively. The evolution of quadrupole deformation in the vicinity of 32Mg is discussed by comparing the present results with the theoretical calculations.