Mapping the deformation in the "island of inversion": Inelastic scattering of Ne 30 and Mg 36 at intermediate energies

The transition strengths of the first-excited 2+ states and deformation lengths of the nuclei Ne30 and Mg36 were determined via Coulomb- and nuclear-force-dominated inelastic scattering at intermediate energies. Beams of these exotic nuclei were produced at the RIKEN Radioactive Isotope Beam Factory and were incident on lead and carbon targets at energies above 200 MeV/u. Absolute excitation cross sections on the lead target yielded reduced transition probabilities of 0.0277(79) and 0.0528(121) e2b2, while the measurements with the carbon target revealed nuclear deformation lengths of δN=1.98(11) and 1.93(11) fm for Ne30 and Mg36, respectively. Corresponding quadrupole deformation parameters of β2∼0.5 from the two probes were found comparable in magnitude, showing no indication for a reduction in deformation along isotopic and isotonic chains from Mg32 towards the neutron drip-line. Comparisons to shell-model calculations illustrate the importance of neutron excitations across the N=20 shell for Ne30 and suggest that shallow maximums of collectivity may occur around N=22 and 24 along the neon and magnesium isotopic chains, respectivelyA.P. is partly supported by MINECO (Spain) Grant No. FPA2014-57196 and Programme “Centros de Excelencia Severo Ochoa” SEV-2012-024