The N = 16 Spherical Shell Closure in 24 O

The unbound excited states of the most neutron-rich dripline oxygen isotope, 24 O, have been investigated by using the 24 O( p , p ′) 24 O * reaction at the beam energy of 62 MeV/nucleon in inverse kinematics. The first and second unbound excited states of 24 O have been observed at E_ x= 4.63_-0.14^+0.30 MeV and E_ x= 5.13_-0.24^+0.19 MeV (preliminary) along with the evidence for another higher lying state at around 7.3 MeV. The quadrupole deformation parameter β_2^+ was deduced to be 0.15_-0.03^+0.08 (preliminary) for the first time. The systematics of the β_2^+ and the E_ x(2_1^+) in the Z = 8 isotopes shows the N = 16 spherical shell closure in 24 O.