The structure of l2C and stellar helium burning

Abstract

The rate of stellar formation of carbon at high temperatures (T > 3 GK) may increase beyond that which is expected from the Hoyle state at 7.654 MeV due to contributions from higher lying states in 12C. The long sought for second 2+ state predicted at 9 – 10 MeV excitation energy in 12C was predicted to significantly increase the production of 12C. An Optical Readout Time Projection Chamber (O-TPC) operating with the gas mixture of CO2 (80%) + N2(20%) at 100 torr with gamma beams from the HIγS facility of TUNL at Duke was used to study the formation of carbon (and oxygen) during helium burning. Preliminary measurements were carried out at beam energies: E = 9.51, 9.61, 9.72, 10.00, 10.54, 10.84 and 11.14 MeV. Extra attention was paid for separating the carbon dissociation events, 12C(γ,3α), from the oxygen dissociation events, 16O(γ, α)12C. Complete angular distributions were measured giving credence to a newly identified 2+ state just below 10.0 MeV.