P. Bender

Excited intruder states in (32)Mg

The low energy level structure of N = 20 32 Mg obtained via β-delayed γ spectroscopy is reported. The level structure of 32 Mg is found to be completely dominated by intruders. An inversion between the 1p-1h and 3p-3h states is observed for the negative parity states, similar to the 0p-0h and 2p-2h inversion for the positive parity states in these N ∼ 20 nuclei. The intruder excited states, both positive and negative parity, are reasonably explained by Monte Carlo shell model calculations, which suggest a shrinking N = 20 shell gap with decreasing Z.

Testing the standard model of nuclear physics

Shell model calculations using optimized effective interactions are becoming the standard model of nuclear structure physics. While earlier effective interactions were optimized for nuclei near the valley of stability, radioactive beam facilities have allowed the study of nuclei much farther from stability. These results suggest that with increasing proton-neutron imbalance significant modifications are needed to the interactions. For example, evidence is mounting that the filling of proton shells modifies the neutron shell structure and vice-versa. The s-d shell provides an excellent testing ground for confronting theory with experiment where intruder structures from higher orbitals have already been recognized, especially in the region where N ~ 2*Z called the “Island of Inversion.” The approach to this region is critical to understanding how the shell structure changes towards inversion. The nucleus 34P with Z = 15 and N = 19 is a key one along this approach. The known level scheme of 34P was doubled i...