Beta-decay studies of very neutron-rich indium isotopes

Beta-decay studies of very neutron-rich indium isotopes The decay of the indium isotopes 133In, 134In, and 135In was investigated experimentally with the aim of providing new insights into the nuclear structure of neutron-rich nuclides from the 132Sn region. Better understanding of these exotic nuclides is required for accurate modeling of the rapid neutron capture nu- cleosynthesis process (r process), due to the A 130 peak in the r-process abundance pattern being linked to the N = 82 shell closure. Because a vast number of nuclei involved in the r-process are -delayed neutron ( n) emitters, new experimental data that can verify and guide theoretical models describing n emission are of particular interest. The e ects of nuclear structure strongly a ecting the competition between neutron emission and -ray deexcitation in the decay of neutron-unbound states were recently observed in the region southeast of 132Sn. The capability of -ray deexcitation to compete with neutron emission well above the neutron-separation energy calls for further investigation, primarily due to its consequences for astrophysical r-process modeling. Neutron-rich indium isotopes constitute excellent cases to address this problem owing to their large -decay energy windows for the population of neutron-unbound states in daughter nuclei (>10MeV), as well as the simplicity of their structure within the shell model. In particular, 134In and 135In { being rare instances of experimentally accessible nuclides for which the -delayed three-neutron decay is energetically allowed { constitute representative nuclei to investigate the competition between -delayed one- and multiple-neutron emission as well as the -ray contribution to the decay of neutron-unbound states. The -delayed -ray spectroscopy measurement was performed at the CERN-ISOLDE facility. The indium isotopes were produced in neutron-induced ssion of the uranium carbide target. Laser-ionized beams of 133In, 134In, and 135In were on-line mass separated and transported to the ISOLDE Decay Station. Isomer-selective ionization provided for 133In enabled two -decaying states in this nucleus to be studied separately for the rst time. Transitions following the decay of indium isotopes were identi ed based on and coincidence data. Decay schemes of 135In and two -decaying states of 133In were established for the rst time, while the decay scheme of 134In was expanded with two -decay branches. Two indium isotopes, 134In and 135In, were identi ed to be -delayed two-neutron emitters. The population of neutron-unbound states decaying via rays was identi ed in 134Sn and 133Sn at excitation energies exceeding the neutron separation energy by 1 MeV. The -delayed one-neutron decay was observed to be the dominant -decay branch of 134In and 135In even though the Gamow-Teller resonance is located substantially above the two- neutron separation energy of the daughter nucleus. The observed dominant one-neutron emission from these nuclei is predicted only by theoretical models, which, apart from the inclusion of rst-forbidden transitions, also consider all possible decay paths of neutron-unbound states. Experimental level schemes of 133Sn, 134Sn, and 135Sn are compared with shell-model predictions, including calculations considering particle- hole excitations across the N = 82 shell gap. Neutron-unbound states corresponding to the couplings of the valence particles to the neutron-core excitations were found to be an important component of the deexcitation pattern observed in daughter nuclei following the decay of neutron-rich indium isotopes.