Orce, José NicolásDyszel, PeterGrzywacz, Robert2025-12-122025-12-122025Dyszel, P., Grzywacz, R., Xu, Z.Y., Kitamura, N., Karny, M., Korgul, A., Madurga, M., Neupane, S., Algora, A., Andreyev, A.N. and Araszkiewicz, M., 2025. First 𝛽-Delayed Two-Neutron Spectroscopy of the 𝑟-Process Nucleus 134In and Observation of the 𝑖13/2 Single-Particle Neutron State in 133Sn. Physical Review Letters, 135(15).https://doi.org/10.1103/l24v-5m31https://hdl.handle.net/10566/21580This manuscript reports on the direct observation of a β-delayed two-neutron emission in a study of ^{134}In at the ISOLDE Decay Station using neutron spectroscopy. We also report on the first measurement in β^{-} decay of the long-sought 13/2^{+} excited state in ^{133}Sn, attributed to be the neutron single-particle i_{13/2} orbital. The observation of sequential neutron emission is used to extract the relative population of the i_{13/2} state, which was found to be much smaller than the predictions of the statistical model. The experiment was possible because of the innovative use of a neutron array with neutron discrimination and interaction tracking capabilities. This is the first study of the details of the two-neutron emission for a nucleus, which belongs to the r-process path. Understanding β-delayed two-neutron emission probabilities is essential to validate models used in astrophysical r-process nucleosynthesis calculations. Observing two-neutron emissions in β^{-} decay paves the way for new experiments to study energy and angular correlations for β-delayed multineutron emitters.enneutronpredictionprobabilityspectroscopystatistical modelArticle