Exotic decay of ${}^{115}\mathrm{Cs}$

The detailed study of the ${\beta }^{+}$/EC decay of the very neutron-deficient and alpha-unbound nucleus ${}^{115}\mathrm{Cs}$ is presented. The measurement was performed at the ISOLDE, CERN where delayed charged particles and $\gamma$ rays were detected. The observed delayed $\gamma$ rays are in agreement with the previously reported characteristics $\gamma$ rays of ${}^{115}\mathrm{Xe}$. Based on the experimental observations, the tentative ground-state spin of ${}^{115}\mathrm{Cs}$ is suggested to be $7/2^{+}$ or ${\mathrm{9/2}}^{+}$. Furthermore, the measured decay branching ratio of delayed protons exceeds the previously reported value. Additionally, new delayed $\alpha$-branching ratio and several reconstructed proton and $\alpha$-unbound excited states of ${}^{115}\mathrm{Xe}$ are being reported for the first time. The properties of proton-unbound states at excitation energies from 3.9–7.9 MeV have been obtained by fitting the delayed proton spectrum via the Bayesian method. The measured lifetimes of these proton-unbound states are in the order of zeptoseconds.

Figure 1

The experimental (IS545) setup at ISOLDE.

Figure 2

$\mathrm{\Delta }\mathrm{E}$-E coincidence spectrum.

Figure 3

$\beta$-gated $\gamma$-ray spectrum.

Figure 4

(Top) The reconstructed proton unbound states of ${}^{115}\mathrm{Xe}$. The solid line represents the fitted one by ${\chi }^2$ minimization. (Bottom) The solid line represents the Bayesian method of analysis.

Figure 5

Corner plot for correlation between partial parameters of the Bayesian analysis.

Figure 6

Decay modes of ${}^{115}\mathrm{Cs}$.