Neutron-upscattering enhancement of the triple-alpha process

Area of Science:

• Nuclear astrophysics
• Stellar nucleosynthesis
• Exotic nuclei

Background:

• The triple-alpha process is crucial for synthesizing carbon in stars.
• The Hoyle state in carbon-12 plays a key role in this process.
• Neutron inelastic scattering and its inverse (neutron upscattering) can influence the Hoyle state's reaction rate.

Purpose of the Study:

• To determine the cross section of the neutron upscattering reaction at astrophysically relevant energies.
• To quantify the enhancement of the triple-alpha reaction rate due to neutron upscattering.
• To assess the astrophysical significance of this enhancement.

Main Methods:

• Utilized detailed balance to determine the cross section, as direct measurement is impossible.
• Employed a highly-collimated monoenergetic neutron beam.
• Used the Texas Active Target Time Projection Chamber (TexAT TPC) filled with CO2 gas to detect 3-alpha particles from Hoyle state decay.

Main Results:

• The neutron upscattering enhancement to the Hoyle state's decay rate was found to be significantly smaller than previously predicted.
• The extracted cross section provides crucial data for nuclear astrophysics models.
• The overall triple-alpha reaction rate enhancement is less significant than anticipated.

Conclusions:

• The astrophysical importance of neutron upscattering enhancement is limited to specific environments, such as neutron star mergers.
• This finding necessitates a re-evaluation of the role of neutron upscattering in stellar evolution models.
• Further research may focus on other reaction pathways or astrophysical sites where this effect could be more pronounced.