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Evidence for a New Compact Symmetric Fission Mode in Light Thorium Isotopes.
A Chatillon1,2, J Taïeb1,2, H Alvarez-Pol3
1CEA, DAM, DIF, F-91297 Arpajon, France.
Physical Review Letters
|June 6, 2020
Summary
Unexpectedly, light thorium isotopes exhibit compact symmetric fission configurations, differing from heavier actinides. This new mode shows a significant 19 MeV drop in fission fragment deformation energy.
Area of Science:
- Nuclear Physics
- Nuclear Chemistry
- Radiochemistry
Background:
- Fission fragment properties are crucial for understanding nuclear stability and decay modes.
- Previous studies on actinide fission predominantly observed elongated scission configurations, especially in symmetric fission.
Purpose of the Study:
- To investigate the scission configurations of thorium isotopes across a range of neutron deficiencies.
- To compare symmetric and asymmetric fission modes in thorium and contrast them with other actinides.
Main Methods:
- Utilizing the R3B/SOFIA setup for coincident measurements of fission fragment mass, nuclear charge, and prompt-neutron multiplicity.
- Analyzing scission configurations inferred from experimental data along the thorium isotopic chain.
Main Results:
- Observed a transition from asymmetric fission in heavier thorium isotopes to symmetric fission in neutron-deficient isotopes.
- Discovered a novel compact scission configuration for symmetric fission in light thorium isotopes, contrary to expectations.
- Quantified a substantial reduction in deformation energy (~19 MeV) for this new symmetric scission mode compared to uranium-plutonium region.
Conclusions:
- The symmetric fission of light thorium isotopes presents a distinct scission mode characterized by compact configurations and reduced deformation energy.
- These findings challenge existing models of nuclear fission and highlight the unique behavior of thorium isotopes.
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