Coulomb dissociation of 16O into 4He and 12C featuring Kathrin Gobel

Abstract:

The fusion reaction of carbon and helium to oxygen is the key to understanding the evolution of stars and the relative abundances of both elements. The reaction rate of ¹²C(a,g)¹⁶O has to be known with an uncertainty of lower than 10% at a center-of-mass energy of 300 keV during Helium burning conditions. So far, experiments have studied the reaction down to about 1 MeV.

We measured the Coulomb dissociation of ¹⁶O into ⁴He and ¹²C at the R3B setup in a first campaign within FAIR Phase-0 at GSI Helmholtzzentrum fur Schwerionenforschung, Darmstadt. The goal was to improve the accuracy of the experimental data and to reach lower center-of-mass energies.

The experiment required beam intensities of one billion ¹⁶O ions per second at an energy of 500 MeV/nucleon. The rare case of Coulomb breakup into ¹²C and ⁴He posed another challenge: we had to detect particles with the same magnetic rigidity as the primary beam, which are not separated by the super-conducting magnet GLAD. Radical changes of the R3B setup were necessary: All detectors had slits to allow the passage of the unreacted ¹⁶O ions, while ⁴He and ¹²C would hit the detectors' active areas. We developed and built detectors based on organic scintillators to track and identify the reaction products with sufficient precision.

The talk reviews the setup and the beamtime, and gives the current status of analysis.

The Seminar will begin at 2pm EST Online Seminar featuring Kathrin Göbel (Goethe University Frankfurt)