First observation of the $\beta$3$\alpha$p decay of ${}^{13}\mathrm{O}$ via $\beta$-delayed charged-particle spectroscopy

Abstract

Background: The $\beta$-delayed proton-decay of ${}^{13}\mathrm{O}$ has previously been studied, but the direct observation of $\beta$-delayed $\alpha$+$\alpha$+$\alpha$+p decay has not been reported. Purpose: Observing rare 3$\alpha$+p events from the decay of excited states in ${}^{13}{\mathrm{N}}^{\star }$ allows for a sensitive probe of exotic highly-clustered configurations in ${}^{13}$N. Method: To measure the low-energy products following $\beta$-delayed 3$\alpha$p-decay, the TexAT Time Projection Chamber was employed using the one-at-a-time $\beta$-delayed charged-particle spectroscopy technique at the Cyclotron Institute, Texas A&M University. Results: A total of $1.9\times 10^5$ ${}^{13}\mathrm{O}$ implantations were made inside the TexAT Time Projection Chamber. 149 3$\alpha$+p events were observed yielding a $\beta$-delayed 3$\alpha +p$ branching ratio of 0.078(6)%. Conclusion: Four previously unknown $\alpha$-decaying states were observed, one with a strong ${}^9\mathrm{B}(g.s)+\alpha$ characteristic at 11.3 MeV, one with a ${}^9\mathrm{B}({\frac{1}{2}}^{+})+\alpha$ nature at 12.4 MeV, and another two that are dominated by ${}^9\mathrm{B}({\frac{5}{2}}^{+})+\alpha$ at 13.1 and 13.7 MeV. Population of the ${\frac{1}{2}}^{+}$ state in ${}^9\mathrm{B}$ has been unambiguously seen, cementing the predicted existence of the mirror-state based on the states observed in ${}^9\mathrm{Be}$.

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