Oxygen Formation in the Light of Gamma-Beams: [Precision Measurements of the ¹²C(α, γ) Reaction with Gamma-Beams and a Time Projection Chamber]

LNS at Avery Point, University of Connecticut, 1084 Shennecossett Rd., Groton, CT 06340, USA

^* e-mail: moshe.gai@uconn.edu. Supported by USDOE grant No. DE-FG02-94ER40870.

Published online: 24 February 2022

Abstract

The carbon/oxygen (C/O) ratio at the end of stellar helium burning is not known with sufficient accuracy due to the large uncertainty in the cross-section of the ¹²C(α, γ)¹⁶O reaction. We developed a new method to measure this reaction that is significantly different from the experimental efforts of the past four decades. Data were measured with vanishingly small background, inside one detector, that also serves as an active target (AT-TPC). Angular distributions of the ¹²C(α, γ)¹⁶O reaction were obtained by measuring the inverse ¹⁶O(γ, α)¹²C reaction with gamma-beams (from the HIγS facility) and an optical readout time projection chamber (O-TPC) detector. We agree with current world data on the measured total reaction cross-section. We further evidence the strength of our method with angular distributions measured over the 1^–resonance at E_cm ~ 2.4 MeV. We extract the E1-E2 mixing phase angle (ϕ₁₂) over this resonance and obtained values that follow the trend of prediction based on unitarity of the scattering amplitude. Our technique promises to yield results that will surpass the quality of the currently available data. We continue these measurements to lower energies at the HIγS facility of TUNL at Duke University, and anticipate measurements down to E_cm = 1.1 MeV at the ELI-NP, the EU facility in Romania..