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First Observation of the Four-Proton Unbound Nucleus ^{18}Mg.
Y Jin1, C Y Niu2, K W Brown2,3
1School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China.
The first observation of the exotic isotope Magnesium-18 (¹⁸Mg) was achieved by analyzing decay events. This finding challenges the stability of the N=8 shell closure in nuclei far from stability.
Area of Science:
- Nuclear Physics
- Exotic Nuclei Research
- Shell Structure Studies
Background:
- Understanding nuclear shell structure is crucial for predicting nuclei properties.
- The N=8 shell closure is a fundamental concept in nuclear physics, but its behavior in nuclei far from stability is less understood.
- Investigating exotic isotopes provides insights into the limits of nuclear stability and shell effects.
Purpose of the Study:
- To report the first observation of the isotope Magnesium-18 (¹⁸Mg).
- To characterize the decay properties of ¹⁸Mg, including its ground-state decay energy and width.
- To investigate the implications of the observed excited state in ¹⁸Mg for the N=8 shell closure.
Main Methods:
- Invariant-mass reconstruction of ^{14}O+4p events.
- Analysis of momentum correlations between decay products.
- Spectroscopic study of the decay energy and width of ¹⁸Mg.
Main Results:
- Magnesium-18 (¹⁸Mg) was observed for the first time.
- The ground-state decay energy and width of ¹⁸Mg were determined to be E_{T}=4.865(34) MeV and Γ=115(100) keV.
- Evidence for an excited state in ¹⁸Mg at 1.84(14) MeV was found, suggesting a weakening of the N=8 shell closure.
Conclusions:
- The observation of ¹⁸Mg provides new data on nuclei far from stability.
- The results suggest a potential demise of the N=8 shell closure in this region.
- Further theoretical and experimental studies are needed to fully understand the impact of Thomas-Ehrman shifts in open systems.
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