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Beta-decay studies of very neutron-rich indium isotopes
The $\beta$ decay of the indium isotopes $^{133}$In, $^{134}$In, and $^{135}$In was investigated experimentally with the aim of providing new insights into the nuclear structure of neutron-rich nuclides from the $^{132}$Sn region. Better understanding of these exotic nuclides is required for accurat...
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Lenguaje: | eng |
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2023
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Acceso en línea: | http://cds.cern.ch/record/2845465 |
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author | Piersa-Silkowska, Monika |
author_facet | Piersa-Silkowska, Monika |
author_sort | Piersa-Silkowska, Monika |
collection | CERN |
description | The $\beta$ decay of the indium isotopes $^{133}$In, $^{134}$In, and $^{135}$In was investigated experimentally with the aim of providing new insights into the nuclear structure of neutron-rich nuclides from the $^{132}$Sn region. Better understanding of these exotic nuclides is required for accurate modeling of the rapid neutron capture nucleosynthesis process ($r$ process), due to the $A \approx 130$ 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 $\beta$-delayed neutron ($\beta n$) emitters, new experimental data that can verify and guide theoretical models describing $\beta n$ emission are of particular interest. The effects of nuclear structure strongly affecting the competition between neutron emission and $\gamma$-ray deexcitation in the decay of neutron-unbound states were recently observed in the region southeast of $^{132}$Sn. The capability of $\gamma$-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 $\beta$-decay energy windows for the population of neutron-unbound states in daughter nuclei ($>$10 MeV), as well as the simplicity of their structure within the shell model. In particular, $^{134}$In and $^{135}$In -- being rare instances of experimentally accessible nuclides for which the $\beta$-delayed three-neutron decay is energetically allowed -- constitute representative nuclei to investigate the competition between $\beta$-delayed one- and multiple-neutron emission as well as the $\gamma$-ray contribution to the decay of neutron-unbound states. The $\beta$-delayed $\gamma$-ray spectroscopy measurement was performed at the CERN-ISOLDE facility. The indium isotopes were produced in neutron-induced fission of the uranium carbide target. Laser-ionized beams of $^{133}$In, $^{134}$In, and $^{135}$In were on-line mass separated and transported to the ISOLDE Decay Station. Isomer-selective ionization provided for $^{133}$In enabled two $\beta$-decaying states in this nucleus to be studied separately for the first time. Transitions following the $\beta$ decay of indium isotopes were identified based on $\beta \gamma$ and $\beta \gamma \gamma$ coincidence data. Decay schemes of $^{135}$In and two $\beta$-decaying states of $^{133}$In were established for the first time, while the decay scheme of $^{134}$In was expanded with two $\beta$-decay branches. Two indium isotopes, $^{134}$In and $^{135}$In, were identified to be $\beta$-delayed two-neutron emitters. The population of neutron-unbound states decaying via $\gamma$ rays was identified in $^{134}$Sn and $^{133}$Sn at excitation energies exceeding the neutron separation energy by 1 MeV. The $\beta$-delayed one-neutron decay was observed to be the dominant $\beta$-decay branch of $^{134}$In and $^{135}$In 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 first-forbidden transitions, also consider all possible decay paths of neutron-unbound states. Experimental level schemes of $^{133}$Sn, $^{134}$Sn, and $^{135}$Sn 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 $\beta$ decay of neutron-rich indium isotopes. |
id | cern-2845465 |
institution | Organización Europea para la Investigación Nuclear |
language | eng |
publishDate | 2023 |
record_format | invenio |
spelling | cern-28454652023-08-08T13:37:07Zhttp://cds.cern.ch/record/2845465engPiersa-Silkowska, MonikaBeta-decay studies of very neutron-rich indium isotopesNuclear Physics - ExperimentThe $\beta$ decay of the indium isotopes $^{133}$In, $^{134}$In, and $^{135}$In was investigated experimentally with the aim of providing new insights into the nuclear structure of neutron-rich nuclides from the $^{132}$Sn region. Better understanding of these exotic nuclides is required for accurate modeling of the rapid neutron capture nucleosynthesis process ($r$ process), due to the $A \approx 130$ 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 $\beta$-delayed neutron ($\beta n$) emitters, new experimental data that can verify and guide theoretical models describing $\beta n$ emission are of particular interest. The effects of nuclear structure strongly affecting the competition between neutron emission and $\gamma$-ray deexcitation in the decay of neutron-unbound states were recently observed in the region southeast of $^{132}$Sn. The capability of $\gamma$-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 $\beta$-decay energy windows for the population of neutron-unbound states in daughter nuclei ($>$10 MeV), as well as the simplicity of their structure within the shell model. In particular, $^{134}$In and $^{135}$In -- being rare instances of experimentally accessible nuclides for which the $\beta$-delayed three-neutron decay is energetically allowed -- constitute representative nuclei to investigate the competition between $\beta$-delayed one- and multiple-neutron emission as well as the $\gamma$-ray contribution to the decay of neutron-unbound states. The $\beta$-delayed $\gamma$-ray spectroscopy measurement was performed at the CERN-ISOLDE facility. The indium isotopes were produced in neutron-induced fission of the uranium carbide target. Laser-ionized beams of $^{133}$In, $^{134}$In, and $^{135}$In were on-line mass separated and transported to the ISOLDE Decay Station. Isomer-selective ionization provided for $^{133}$In enabled two $\beta$-decaying states in this nucleus to be studied separately for the first time. Transitions following the $\beta$ decay of indium isotopes were identified based on $\beta \gamma$ and $\beta \gamma \gamma$ coincidence data. Decay schemes of $^{135}$In and two $\beta$-decaying states of $^{133}$In were established for the first time, while the decay scheme of $^{134}$In was expanded with two $\beta$-decay branches. Two indium isotopes, $^{134}$In and $^{135}$In, were identified to be $\beta$-delayed two-neutron emitters. The population of neutron-unbound states decaying via $\gamma$ rays was identified in $^{134}$Sn and $^{133}$Sn at excitation energies exceeding the neutron separation energy by 1 MeV. The $\beta$-delayed one-neutron decay was observed to be the dominant $\beta$-decay branch of $^{134}$In and $^{135}$In 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 first-forbidden transitions, also consider all possible decay paths of neutron-unbound states. Experimental level schemes of $^{133}$Sn, $^{134}$Sn, and $^{135}$Sn 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 $\beta$ decay of neutron-rich indium isotopes.CERN-THESIS-2021-359oai:cds.cern.ch:28454652023-01-06T10:14:36Z |
spellingShingle | Nuclear Physics - Experiment Piersa-Silkowska, Monika Beta-decay studies of very neutron-rich indium isotopes |
title | Beta-decay studies of very neutron-rich indium isotopes |
title_full | Beta-decay studies of very neutron-rich indium isotopes |
title_fullStr | Beta-decay studies of very neutron-rich indium isotopes |
title_full_unstemmed | Beta-decay studies of very neutron-rich indium isotopes |
title_short | Beta-decay studies of very neutron-rich indium isotopes |
title_sort | beta-decay studies of very neutron-rich indium isotopes |
topic | Nuclear Physics - Experiment |
url | http://cds.cern.ch/record/2845465 |
work_keys_str_mv | AT piersasilkowskamonika betadecaystudiesofveryneutronrichindiumisotopes |