Abstract
-delayed one-neutron and two-neutron branching ratios and have been measured in the decay of to 87 Ga isotopes at the Radioactive-Isotope Beam Factory (RIBF) at the RIKEN Nishina Center using a high-efficiency array of neutron counters (BRIKEN). Two-neutron emission was observed in the decay of for the first time and the branching ratios were measured to be , and , respectively. One-neutron branching ratio of and half-life of 29(4) ms were measured for the first time. The branching ratios of were also measured to be and with better precision than a previous study. The observation that for both was unexpected and is interpreted as a signature of dominating one-neutron emission from the two-neutron unbound excited states in . In order to interpret the experimental results, shell-model and Hauser-Feshbach statistical model calculations of delayed particle and -ray emission probabilities were performed. This model framework reproduces the experimental results. The shell model alone predicts significantly larger than for the decay, and it is necessary to invoke a statistical description to successfully explain the observation that . Our new results demonstrate the relevance and importance of a statistical description of neutron emission for the prediction of the decay properties of multineutron emitters and that it must be included in the -process modeling.
- Received 24 July 2018
- Revised 18 January 2019
DOI:https://doi.org/10.1103/PhysRevC.100.031302
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