Neutron-upscattering enhancement of the triple-alpha process

Abstract

The neutron inelastic scattering of carbon-12, populating the Hoyle state, is a reaction of interest for the triple-alpha process. The inverse process (neutron upscattering) can enhance the Hoyle state’s decay rate to the bound states of 12C, effectively increasing the overall triple-alpha reaction rate. The cross section of this reaction is impossible to measure experimentally but has been determined here at astrophysically-relevant energies using detailed balance. Using a highly-collimated monoenergetic beam, here we measure neutrons incident on the Texas Active Target Time Projection Chamber (TexAT TPC) filled with CO2 gas, we measure the 3α-particles (arising from the decay of the Hoyle state following inelastic scattering) and a cross section is extracted. Here we show the neutron-upscattering enhancement is observed to be much smaller than previously expected. The importance of the neutron-upscattering enhancement may therefore not be significant aside from in very particular astrophysical sites (e.g. neutron star mergers).

Photonuclear reactions with charged particles detection for nuclear astrophysics studies

“…The use of TPCs for the measurement of photon-induced reactions is very similar to the use of TPCs for neutron-induced reactions, since the beam is neutral in both cases. Noteworthy examples TPCs that have been utilized for the measurement of neutron-induced reactions are the Neutron Induced Fission Fragment Tracking Experiment (NIFTE) [50] and the Texas Active Target (TexAT) [51,52]. These detectors, typically have a solid angle coverage approaching 4π, and permit the use of thick, gaseous targets without worsening the energy resolution.…”