Electroexcitation of odd-parity states in 27Al

Inelastic electron scattering form factors were measured for the low-lying odd-parity states of 27Al over a momentum transfer range of 0.57 to 2.41 fm-1. Reduced ground-state transition probabilities were deduced for states at 4.055 MeV(1/2-), 5.156 MeV(3/2-), 6.159 MeV(3/2-), 6.477 MeV(7/2-), 6.605 MeV(1/2- or 3/2-), 6.651 MeV(5/2-), 6.993 MeV(3/2-), and 7.228 MeV(9/2-). In addition, the results support odd-parity assignments for the 5.827 MeV(3/2- or 5/2+) and 7.477 MeV(7/2) levels. Attempts have been made to interpret the results in terms of the weak-coupling and strong-coupling models. The measurements confirm the apparent high concentration of 1p-shell proton hole strength in the 4.055 MeV,1/2- and 5.156 MeV,3/2- states. To satisfactorily account for the observed properties of these two levels using the weak-coupling model requires an anomalously small value of 1.35 MeV for the spin-orbit splitting of the 1p shell. The structure of levels in the 6 to 7.5 MeV region is shown to be based on the excitation of 1d-shell nucleons into the 1f shell