Radiative Width of the Hoyle State from γ-Ray Spectroscopy

Area of Science:

• Nuclear Physics
• Astrophysics
• Quantum Mechanics

Background:

• The Hoyle state in carbon-12 (¹²C) is crucial for understanding stellar nucleosynthesis, particularly the triple-alpha process.
• Accurate determination of its properties, like radiative width, is essential for refining astrophysical models.

Purpose of the Study:

• To precisely measure the radiative branching ratio of the Hoyle state in ¹²C.
• To determine the radiative width of the Hoyle state using experimental data and existing values.
• To assess the impact of the new radiative width on stellar evolution models.

Main Methods:

• Excitation of the Hoyle state in ¹²C via the ¹²C(p,p') reaction at 10.7 MeV proton energy.
• Measurement of cascading 3.21 and 4.44 MeV electric quadrupole transitions.
• Analysis of proton-gamma-gamma triple coincidence data to determine the radiative branching ratio.

Main Results:

• Observed cascading electric quadrupole transitions from the Hoyle state in ¹²C.
• Obtained a radiative branching ratio Γ_{rad}/Γ = 6.2(6)×10⁻⁴.
• Determined the radiative width of the Hoyle state as Γ_{rad} = 5.1(6)×10⁻³ eV, approximately 34% higher than previously accepted values.

Conclusions:

• The experimentally determined radiative width of the Hoyle state is significantly higher than current estimates.
• This revised value necessitates adjustments in models of stellar evolution and nucleosynthesis.
• Further investigation into the Hoyle state's properties may refine our understanding of carbon production in stars.