Speaker
Description
Thermonuclear reactions that power the stars take place at different energies according to their respective stellar environments. Such energies are well below the Coulomb barrier and the respective cross-sections are extremely small, often below experimental reach. Modelling energy production in stars requires experimental data on cross-sections for low energies; these data are sparse. As a consequence extrapolations are made, with a large degree of unavoidable uncertainty. Of special interest are (p, gamma) and (alpha, gamma) reactions, in particular those that regulate the ratio of C and O and those that burn 18O and, therefore, regulate the ratio between 16O and 18O in the Universe. One of the benchmark reactions to be investigated in this work is the 12C(alpha,gamma)16O at energies down to 1 MeV in the centre-of-mass reference frame.
A new active target detector (time-projection chamber - TPC) optimised for experiments with high-intensity gamma-ray beams was developed and built at the University of Warsaw [1] to study time-inverse (gamma,p) and (gamma, alpha) stellar reactions.
The dectector uses a 3-coordinate planar electronic readout acting as virtual pixels, read-out by GET electronics with negligible dead-time for the reaction rates (incl. background) expected for the reactions of interest with the available high-intensity gamma beams. Moreover, it can work with pure CO2 gas at pressures as low as 80 mbar.
The detector was employed in 2022 in a campaign of measurements at the High Intensity Gamma-Ray Source (HIgS) facility at the Triangle Universities Nuclear Laboratory (TUNL), Durham, NC, USA. The time-inverse photo-disintegration processes induced by high energy photons were studied, using a monochromatic gamma-ray beam at energies ranging from 8.51 to 13.9~MeV, well beyond the previously-established limit [2]. The beam interacted with the CO2 gas in the chamber, where the charged reaction products, namely 12C and alpha particles, were detected, and their momenta reconstructed in 3D. The principles of the experiment will be described, together with preliminary results. An outlook on future plans will be given.
[1] M. Cwiok et al., Acta Phys. Pol. 49 (2018) 509.
[2] R. Smith et al., Nature Comm. 12, 5920 (2021) and M. Gai, NPA10 contribution
