Isospin Symmetry Breaking Disclosed in the Decay of Three-Proton Emitter Al 20

Résumé fourni par la source

The previously unknown nucleus ^{20}Al has been observed for the first time by detecting its in-flight decays. Tracking trajectories of all decay products with silicon microstrip detectors allowed for a conclusion that ^{20}Al is unbound with respect to three-proton (3p) emission. The 3p-decay energy of the ^{20}Al ground state has been determined to be 1.93(_{-0.10}^{+0.12}) MeV through a detailed study of angular correlations of its decay products, ^{17}Ne+p+p+p. This value is significantly smaller than the predictions inferred from the isospin symmetry by using the known neutron separation energy of its mirror nucleus ^{20}N, which indicates a possible isospin symmetry breaking in the mirror nuclei ^{20}Al and ^{20}N. This observed isospin symmetry breaking is supported by the calculations of the continuum embedded theoretical frameworks, describing the observed ^{20}Al ground state as a 1p s-wave state with a spin-parity of 1^{-}, which differs from the spin-parity (2^{-}) of the ^{20}N ground state. The ^{20}Al ground state decays by sequential 1p-2p emission via the intermediate ground state of ^{19}Mg, which is the first observed case of "daughter" 2p radioactivity following 1p decay of the parent state.

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