Enhanced γ-Ray Emission from Neutron Unbound States Populated in β Decay

Area of Science:

• Nuclear Physics
• Nuclear Astrophysics
• Spectroscopy

Background:

• Investigating beta-decay processes and gamma-ray emission is crucial for understanding nuclear structure.
• Accurate measurements of gamma branching ratios are essential for nuclear reaction models.

Purpose of the Study:

• To measure beta-decay intensity to states above the neutron separation energy followed by gamma-ray emission in (87,88)Br and (94)Rb.
• To compare experimental gamma branching with Hauser-Feshbach model calculations.
• To investigate discrepancies in neutron-rich nuclei and their implications for nuclear astrophysics.

Main Methods:

• Total absorption spectroscopy was employed to achieve accurate results.
• Systematic errors were carefully controlled.
• Hauser-Feshbach model calculations were used for comparison.

Main Results:

• Unexpectedly large gamma intensities were observed in all three isotopes, extending beyond hindered neutron penetration regions.
• (87)Br and (88)Br showed gamma branching of 57% and 20%, potentially due to nuclear structure effects.
• For neutron-rich (94)Rb, the observed 4.5% branching significantly exceeded standard model predictions, requiring a tenfold enhancement in the photon strength to neutron strength ratio.

Conclusions:

• The observed gamma branching suggests nuclear structure effects in (87,88)Br.
• Discrepancies in (94)Rb indicate a need for revised nuclear statistical models for neutron-rich nuclei.
• An enhanced photon strength function in neutron-rich nuclei could impact (n,γ) cross sections and r-process abundance calculations.