Influence of the neutron f_7/2 subshell on the structure of ²⁸Mg

Excited states in ²⁸Mg were studied in an experiment at the ISAC-II facility at TRIUMF to investigate the evolution of the f_7/2 orbital as a function of neutron excess near the N=20 island of inversion. For the first time ²⁸Mg was investigated using ¹²C(¹⁸O,2p)²⁸Mg fusion-evaporation, leading to preferential population of states at high spin and excitation energy where the influence of the f_7/2 subshell is expected.

Data corresponding to ²⁸Mg was extracted by gating on protons and gamma rays. Proton gating was achieved utilizing a new CsI(Tl) scintillator array, part of the TIGRESS Integrated Plunger (TIP) infrastructure. TIP was coupled with the TIGRESS array of HPGe clovers for gamma-ray detection. Coincidence spectroscopy was performed from Doppler corrected gamma-ray spectra taken using a thin target. Lifetime measurements were performed via the Doppler shift attenuation method using a second target with a thick gold backing.

Angular distribution measurements and comparisons to levels in neighboring isotopes indicate that new candidates for the yrast 6⁺ state and negative parity states are observed. A high precision measurement of the lifetime of the yrast 4⁺ state and new lifetime limits for higher lying states were also obtained. Detailed results will be presented.