Observation of Two-Proton Radioactivity of Mg-19 by Tracking the Decay Products

We have observed the two-proton radioactivity of the previously unknown {sup 19}Mg ground state by tracking the decay products in-flight. For the first time, the trajectories of the 2p-decay products, {sup 17}Ne+p+p, have been measured by using tracking microstrip detectors which allowed us to reconstruct the 2p-decay vertices and fragment correlations. The half-life of {sup 19}Mg deduced from the measured vertex distribution is 4.0(15) ps in the system of {sup 19}Mg. The Q value of the 2p decay of the {sup 19}Mg ground state inferred from the measured p-p-{sup 17}Ne correlations is 0.75(5) MeV.