14N(p,γ)15O at Bellotti Ion Beam Facility
PI: Gyürky György
Astrophysical Motivation
The 14N(p,γ)15O, being the slowest reaction of the CNO cycle, gives the major nuclear contribution to the uncertainty budget in the estimation of the C and N abundances in the Sun using direct Solar CNO neutrino measurements like the one performed by the Borexino collaboration. Up to the current days, R-matrix analyses of the cross section failed to provide a consistent view of both the low and high energy data for the 14N(p,γ)15O reaction. The biggest source of uncertainty in the cross-section extrapolation to astrophysical energies lies both in the limited understanding of the weaker transitions and in the lack of angular distribution data especially for the ground state transition at low energies.
Experimental Aims
The goal of the experiment was thus to measure the reaction cross section in a wide energy range, putting special emphasis also on the weaker transitions and studying the angular distribution. The experiment has been implemented in two complementary phases: A first campaign focused on the measurement of the excitation function using one HPGe detector in close geometry. The second phase is dedicated to the study of the angular distribution using three HPGe detectors. The first beamtime for 14N(p,γ)15O started in June 2023, this was the first time ever when beam was delivered to scientific users of the Bellotti IBF. Further campaigns up to July 2024 are devoted to the completion of the second phase.
Experimental setup
For the cross section measurements, solid state nitrogen targets were bombarded by the proton beam with hundreds of A intensity provided by the BIBF accelerator. The targets were made either by implantation or by the novel technique of TaN production using enriched 14N gas. For the angular detection of the gamma-radiation, a dedicated setup has been designed allowing the positioning of the detectors at various angles and distances. In the first phase, cross section data were collected with one HPGe detector placed at 55° in the energy range Ep = 0.25−1.5MeV. In the second phase of the experiment, the angular distribution of the most important transitions is measured with three HPGe detectors at five angles, in a similar energy range, where no literature data are available.
