Current Data on the

Seventy years after the seminal (1954) “Hoyle Paper”, emphasizing the importance of the 12C(α,γ) reaction, Fifty years after the seminal (1974) work of Dyer and Barnes and forty years after Fowler declared (1984) the 12C(α,γ) Reaction “of paramount importance in nuclear astrophysics”, we still do not know with sufficient accuracy the gamma-capture 12C(α,γ) reaction at low energies. Most disturbing is the disagreement of the measured E1-E2 interference phase angle (ϕ12) with an elementary prediction of quantum mechanics. We developed a new method for measuring the cross section of this reaction by measuring the inverse 16O(γ,α) reaction with TPCs operating in gamma-beams. It was measured initially with the UConn-TUNL-Weizmann-PTB optical readout TPC (O-TPC) operating as an active target with 100 torr CO2 or N2O + N2(20%) gas admixture, placed in the gamma beam of the HIγS/TUNL at Duke University. Most recently the O-TPC was decommissioned and replaced by the Warsaw electronic readout TPC (eTPC). Using the O-TPC we demonstrated the validity of our new method and benchmarked it against world data, with the measured total reaction cross section that agrees with the world data. Angular distributions measured with unprecedented accuracy with the O-TPC operating with N2O gas and the Warsaw eTPC operating with pure CO2 gas, reveal the E1-E2 mixing phase angle (ϕ12) that for the first time agrees with the prediction of unitarity over the entire measured energy range (Ecm = 1.4 - 5.0 MeV). These measurements that will require more than 109 γ/s, will continue during the summer of 2026 to lower energies, for an accurate extrapolation to stellar energy (300 keV).