Competition between Allowed and First-Forbidden β Decay: The Case of ^{208}Hg→^{208}Tl

Area of Science:

• Nuclear Physics
• Nuclear Astrophysics

Background:

• Investigating nuclear structure and decay properties of neutron-rich nuclei is crucial for understanding nucleosynthesis.
• The N>126, Z<82 region is key for understanding the rapid neutron capture process.

Purpose of the Study:

• To investigate the beta decay of ^{208}Hg into _{81}^{208}Tl.
• To validate shell-model calculations and proton-neutron interactions in this mass region.
• To study the competition between different beta decay modes and their impact on nucleosynthesis.

Main Methods:

• Experimental investigation of ^{208}Hg beta decay at CERN-ISOLDE.
• Comparison of experimental data with theoretical shell-model calculations.

Main Results:

• The deduced level scheme of _{81}^{208}Tl was well described by shell-model calculations.
• Only three negative parity states were populated directly in the beta decay, contrary to expectations.
• A unique parity-changing 0^{+}→0^{-} beta decay involving a core-excited state was observed.

Conclusions:

• The study validates the employed proton-neutron interactions, with implications for neutron-rich nuclei.
• The data provide a unique test for understanding beta decay processes relevant to heavy element nucleosynthesis.
• The observed unique decay can offer insights into mesonic corrections in effective operators.