Revisit to two-proton radioactivity of ¹⁹Mg and observation of two-proton decay of ³⁰Ar

An experiment aimed to investigate the two-proton (2p) decay of the previously unknown nucleus ³⁰Ar was performed at GSI: By tracking the decay products in-flight with silicon micro-strip detectors, the 2p decays of ³⁰Ar were observed for the first time. For the calibration purpose, 2p decays of ¹⁹Mg were also remeasured by tracking the coincident ¹⁷Ne+p+p trajectories. By comparing the measured angular p-¹⁷Ne correlations with those obtained from the corresponding Monte Carlo simulations, the simultaneous 2p decay of ¹⁹Mg ground state and the sequential 2p emission of several known excited states of ¹⁹Mg were confirmed. One new excited state in ¹⁹Mg and two new excited states in ¹⁸Na were observed. (authors)