Observation of excited states in Mg20 sheds light on nuclear forces and shell evolution

The exotic Borromean nucleus Mg20 with N=8, located at the proton drip line provides a unique testing ground for nuclear forces and the evolution of shell structure in the neutron-deficient region. We report on the first observation of proton unbound resonances together with bound states in Mg20 from the Mg20(d,d′) reaction performed at TRIUMF. Phenomenological shell-model calculations offer a reasonable description. However, our experimental …