1p3/2 proton-hole state in 132Sn and the shell structure along N = 82

Area of Science:

• Nuclear Physics
• Nuclear Structure
• Astrophysical Nucleosynthesis

Background:

• 132Sn is a doubly magic nucleus, serving as a reference for nuclear structure studies.
• Proton hole nuclei near 132Sn provide insights into nuclear shell effects and deviations from simple models.
• Understanding N=82 isotones is crucial for modeling the rapid neutron-capture (r-process) nucleosynthesis.

Purpose of the Study:

• To identify and characterize a new low-lying state in the 131In nucleus.
• To investigate the nuclear structure of experimentally inaccessible N=82 isotones below 132Sn.
• To explore the evolution of the N=82 shell gap in the context of the r-process.

Main Methods:

• Observation of gamma decay from a newly identified state in 131In.
• Populating the state via beta decay of 131Cd and beta-delayed neutron emission from 132Cd.
• Performing shell-model calculations using newly obtained experimental data.

Main Results:

• A new state in 131In was identified at an excitation energy of 1353 keV.
• This state is characterized as the previously unknown πp3/2 single-hole state relative to the 132Sn core.
• Shell-model calculations revealed a surprising lack of proton subshell closures in the N=82 isotone chain.

Conclusions:

• The identified πp3/2 single-hole state in 131In provides critical experimental data for nuclear structure models.
• The absence of predicted proton subshell closures challenges current nuclear structure theories for this region.
• This finding has significant implications for the predicted N=82 shell gap evolution and r-process element abundances.