From nuclear reactions to astrophysics

Studies of stellar processes using charged-particle and gamma-ray spectroscopy Speaker: Christian Aa. Diget, Department of Physics, University of York, UK Time: Wednesday, May 18 at 15.15-16.00 Location: Building 1520-516 Nuclear processes driving the energy production and nuclear synthesis in stars often cannot be studied directly in the laboratory. This is because the reactions in many cases involve short-lived nuclei, and are furthermore hindered by the Coulomb repulsion of the nuclei, making direct observation of the reactions difficult or even impossible. In this category are the reactions related to the breakout from the Hot-CNO cycle in for example X-ray bursts, a nuclear run-away on the surface of neutron stars. Instead of direct measurements the reactions must be studied indirectly, typically in reaction studies which probe the nuclear structure that determine the astrophysical processes. The Silicon Highly-segmented Array for Reactions and Coulex (SHARC) [1] is a new multipurpose array for charged-particle detection designed to address a diverse set of outstanding nuclear-physics questions, including indirect studies of astrophysical reactions and studies of nuclear structure. The array is used for radioactive-ion-beam studies at the ISAC-II accelerator at TRIUMF, Canada [2] in conjunction with the TIGRESS -ray spectrometer [3]. The first experiments utilising the array have now been completed using a range of different reactions such as transfer of neutrons, a deuteron, or an alpha particle as well as utilizing deep inelastic scattering of radioactive nuclei on a heavy target. Specific examples are the newly performed indirect study of the Hot-CNO breakout reactions 18Ne + alpha ! 21Na +proton reaction and the planned 15O + alpha ! 19Ne + gamma reaction study. [1] C. Aa. Diget, et al., J. Inst. 6, P02005 (2011). [2] R. Laxdal, et al., in Proceedings of LINAC08, Victoria, BC, Canada (2008), p. 97. [3] C. E. Svensson, et al., J. Phys. G 31, S1663 (2005). _________________________________________________________ Hans Fynbo