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p-sd Shell gap reduction in neutron-rich systems and cross-shell excitations in 20 O
M Wiedeking1, S L Tabor, J Pavan
1Florida State University, Tallahassee, Florida 32306, USA.
Physical Review Letters
|May 21, 2005
Summary
Researchers studied excited states in Oxygen-20 using nuclear reactions. New states were found, suggesting core-excited configurations and a shrinking shell gap in neutron-rich isotopes.
Area of Science:
- Nuclear Physics
- Atomic Physics
Background:
- Investigating the structure of neutron-rich nuclei provides insights into nuclear forces.
- The Oxygen-16 core is a key reference point for nuclear shell structure.
Purpose of the Study:
- To explore excited states in the neutron-rich Oxygen-20 nucleus.
- To investigate core-excited configurations and their implications for nuclear structure.
Main Methods:
- Nuclear reaction: 10Be(14C,alpha) at Florida State University (FSU).
- Detection systems: Particle telescope (Si surface barrier detectors) and FSU gamma detector array.
- Analysis of alpha-gamma and alpha-gamma-gamma coincidence data.
Main Results:
- Five new excited states in 20O were identified below 6 MeV.
- Shell model calculations indicate these states are primarily 1p-1h core-excited configurations.
- Experimental data and calculations show a reduction in the p-sd shell gap for neutron-rich O and F isotopes.
Conclusions:
- The observed states in 20O are consistent with core-excited configurations.
- A trend of decreasing p-sd shell gap with increasing neutron number is observed in Oxygen and Fluorine isotopes.