Neutron-upscattering enhancement of the triple-alpha process

The inelastic scattering of neutrons on 12C that populates the Hoyle state can, via the inverse process (neutron upscattering), enhance the Hoyle-state decay to bound states of 12C and thereby increase the triple-alpha reaction rate. Although the direct neutron-upscattering cross section cannot be measured, we determine it at astrophysically relevant energies using detailed balance. Using a highly collimated, quasi-monoenergetic neutron beam incident on the TexAT TPC filled with CO2 gas, we detect the three alpha particles from Hoyle-state decay following inelastic scattering and extract the 12C(n,n2)3α cross section. We find the neutron-upscattering enhancement is much smaller than previously expected, implying limited significance except in specific astrophysical environments such as neutron star mergers.