Investigating Collectivity in ^30,31Na via Heavy-Ion Inelastic Scattering

Near the line of β-stability, nuclei possessing magic numbers are expected to exhibit spherical ground states, accompanied with reduced B(E2) values for low-lying excitations. However, as one approaches the so-called island of inversion, comprising of neutron-rich nuclei near N=20, notable enhancements in measured B(E2) values and ground-state quadrupole moments emerge as anomalous features. In this region, such behavior has been attributed to the evolution of the ground state from a spherical sd-shell configuration to deformed sd-fp shell configurations [1,2]. To study these phenomena, a heavy-ion inelastic scattering measurement on neutron-rich ^30,31Na isotopes at N=19,20 was conducted at the NSCL with a modified recoil distance setup utilizing the TRIPLEX device, GRETINA, and the S800 spectrograph.We measured the E2 transition rates within members of suggested rotational bands built on the K=2 ground state in ³⁰Na and the K=3/2 ground state in ³¹Na [3,4]. The measured E2 transition rates allow us to further discern the role of collective modes in the low-lying transitions and the extent of ground-state deformation near N=20. A preliminary result of the experimental cross sections for ^30,31Na will be presented alongside a discussion on extracted B(E2) values with available theoretical calculations.

[1] E. K. Warburton, J.A. Becker, B. A. Brown, Phys. Rev. C 41 (1990) 1147.

[2] T. Otsuka, A. Gade, O. Sorlin, T. Suzuki, Y. Utsuno, Rev. Mod. Phys. 92 (2020) 015002.

[3] M. Seidlitz et. al., Phys. Rev. C 89 (2014) 024309.

[4] B. V. Pritychenko et. al., Phys. Rev. C 63 011305(R).