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First Exploration of Monopole-Driven Shell Evolution above the N=126 Shell Closure: New Millisecond Isomers in
T T Yeung1,2, A I Morales3, J Wu4,5
1Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan.
Researchers explored heavy neutron-rich nuclei near the N=126 shell closure, discovering new millisecond isomers in Tl isotopes. This provides the first experimental evidence of shell evolution in this unexplored nuclear region.
Area of Science:
- Nuclear Physics
- Atomic Physics
- Spectroscopy
Background:
- Investigating nuclei beyond the N=126 shell closure is crucial for understanding nuclear structure.
- Previous studies have limited data on neutron-rich isotopes in this region.
Purpose of the Study:
- To perform isomer spectroscopy on heavy neutron-rich nuclei beyond the N=126 shell closure.
- To identify new isomers and characterize their properties, providing insights into nuclear shell evolution.
Main Methods:
- Utilized isomer spectroscopy at the Radioactive Isotope Beam Factory (RIBF) at RIKEN.
- Identified new millisecond isomers in ^{213}Tl and ^{215}Tl.
Main Results:
- Discovered new millisecond isomers at low excitation energies in ^{213}Tl (985.3 keV) and ^{215}Tl (874 keV).
- Measured half-lives of 1.34(5) ms for ^{213}Tl and 3.0(3) ms for ^{215}Tl, suggesting 11/2^{-} spin-parity.
- Observed population via E1 transitions from higher-lying 17/2^{+} states, linked to proton-hole configurations.
Conclusions:
- The observed lowering of 11/2^{-} states is attributed to changes in proton-neutron monopole interactions as neutron orbitals fill.
- These findings offer the first experimental evidence of shell evolution in the N>126 nuclear region.
- The study opens new avenues for exploring the nuclear landscape below doubly magic ^{208}Pb.
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