Elastic alpha-12C scattering and the 12C(alpha,gamma)16O E2 S factor

Area of Science:

• Nuclear Physics
• Astrophysics
• Quantum Mechanics

Background:

• Understanding nuclear reactions is crucial for astrophysics, particularly for nucleosynthesis in stars.
• The 12C(alpha,alpha)12C reaction provides insights into the structure of 16O, a key element in stellar evolution.

Purpose of the Study:

• To precisely measure angular distributions of 12C(alpha,alpha)12C elastic scattering.
• To determine the reduced width amplitude of the Ex = 6.917 MeV (2+) state in 16O using R-matrix analysis.
• To calculate the S factor for radiative alpha capture, considering interference effects.

Main Methods:

• Experimental measurement of elastic scattering yields for 12C(alpha,alpha)12C over a range of energies and angles.
• R-matrix analysis to extract nuclear parameters, including reduced width amplitude and interaction radius.
• Calculation of the S factor using determined parameters and existing data on radiative alpha capture and beta-delayed alpha-decay.

Main Results:

• Angular distributions were measured with 12,864 data points.
• The reduced width amplitude gamma12 for the Ex = 6.917 MeV (2+) state in 16O was determined as 0.47 +/- 0.06 MeV(1/2).
• A deep minimum for the interaction radius was found at a = 5.42(+0.16)(-0.27) fm.
• The S factor was calculated to be S(E2)(300) = 53(+13)(-18) keV b at E(c.m.) = 300 keV.

Conclusions:

• The study provides precise experimental data and analysis for the 12C(alpha,alpha)12C reaction.
• The determined parameters refine our understanding of the 16O nuclear structure.
• Calculated S factor aids in modeling nucleosynthesis processes in stars, particularly concerning carbon and oxygen interactions.