Complementary studies of T=2 ³⁰Al and the systematics of intruder states

Low-spin states were studied in ³⁰Al following the β decay of ³⁰Mg produced in the fragmentation of 140-MeV/AMU ⁴⁸Ca. Analysis of the β-γ and β-γ-γ coincidences revealed a new 1⁺ state at 2413 keV, confirmation of the level scheme, and a more accurate half-life measurement of 315(6) ms for the ³⁰Mg ground state. Higher-spin states were investigated in the reaction of ¹⁴C on ¹⁸O at 22 MeV. Protons and deuterons were detected in a segmented E-ΔE Si telescope in coincidence with one or two γ rays in the FSU Ge detector array. A comparison of the resulting level and decay scheme with predictions of the sd shell model shows good agreement with all but six of the states in both excitation energy and γ-decay branching ratios. The root-mean-square deviations in energy of these states using the older USD and newer USDA and USDB interactions were 265, 176, and 173 keV, respectively. The remaining six states are well described as 4^- to 7^- states, similar in relative energy to those in ²⁸Al but shifted down by about 1200 keV. These states also agree well with the predictions of shell-model calculations using the WBP interaction. A comparison of the lowest 4^- states in even A Na, Al, and P isotopes shows a systematic decrease in energy with increasing N and with decreasing Z. The energies of the 4^- states are almost identical in nuclei with the same N-Z values.