Physical Review Letters ( IF 8.385 ) Pub Date :
J. Lee et al.

$\beta$-delayed one-proton emission of ${}^{22}$Si, the lightest nucleus with an isospin projection T${}_{z}$=-3, was studied with a silicon array surrounded by high-purity germanium detectors. Properties of $\beta$-decay branches and the reduced transition probabilities for the transitions to the low-lying states of ${}^{22}$Al were determined. Comparing to the mirror $\beta$-decay of ${}^{22}$O, the by-far largest value of mirror asymmetry in low-lying states with $\delta$=$209\left(96\right)%$ is found in the transition to the first ${1}^{+}$ excited state. Shell model calculation with isospin-nonconserving (INC) forces including the $T$=1, $J$=2,3 interaction related to the ${s}_{1/2}$ orbit, which introduces explicitly the isospin-symmetry breaking force and describes loosely-bound nature in the wave functions of the ${s}_{1/2}$ orbit, can well reproduce the observed data, and consistently explain the observation that large $\delta$ value occurs only for the first, but not for the second ${1}^{+}$ excited state of ${}^{22}$Al. Our results, while supporting the proton-halo structure in ${}^{22}$Al, might provide another means for identification of halo nuclei.

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